1506 servo 06 2015

Personal CNC Mills Prototyping - Product Design - R&D - Engineering Shown here is an articulated humanoid robot leg, built by researchers at the Drexel Autonomous System Lab (DASL) with a Tormach PCNC 1100 milling machine. DASL researcher Roy Gross estimates that somewhere between 300 and 400 components for “HUBO+� have been machined on their PCNC 1100. To learn more about this project, visit www.tormach.com/servo.

PCNC 1100 Series 3

PCNC 770 Series 3

Mills shown here with optional stand and accessories.

www.tormach.com/servo

06.2015 VOL. 13

NO. 6

Columns 08 Ask Mr. Roboto

by Dennis Clark

Your Problems Solved Here Wrapping up the 4D Systems’ uCAM-II serial camera project.

70 Twin Tweaks

by Bryce and Evan Woolley

The Force Servo Arm Awakens Not only is the force strong with this device, it can handle fragile cargo as well.

76 Then and Now

by Tom Carroll

Prototyping and Building a Robot Read about how robot experimenters can develop and/or refine their robot’s mechanical design by utilizing existing robot platforms and products to build upon.

69 MaxRoboTech Comics Having Fun, That’s What!

Departments 06 Mind/Iron Disposable Drones

07 Events Calendar 10 New Products 11 Showcase 66 SERVO Webstore 82 Robo-Links 82 Advertiser’s Index

PAGE 76

PAGE 70

The Combat Zone 16 The Influence of Combat Robot Kits 19 Skill Building — Drive Better 21 Quality Versus Quantity — Or, Why One Axle is Sometimes Better Than Two

12 Bots in Brief • Move Over, Million Dollar Man • You’re So Caddy • Swashbuckling Bot • Net Results • Robots Do DARPA • Flower Power • Get Hosed • Jumping Jerboas!

SERVO Magazine (ISSN 1546-0592/CDN Pub Agree#40702530) is published monthly for $24.95 per year by T & L Publications, Inc., 430 Princeland Court, Corona, CA 92879.

PERIODICALS POSTAGE PAID AT CORONA, CA AND AT ADDITIONAL ENTRY MAILING OFFICES. POSTMASTER: Send address changes to SERVO Magazine, P.O. Box 15277, North Hollywood, CA 91615 or Station A, P.O. Box 54, Windsor ON N9A 6J5; cpcreturns@servomagazine.com

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SERVO 06.2015

In This Issue ...

PAGE 26

26 RoboGames 2015

by Camp Peavy, with contributions from Bob Allen and Michael Mauldin Like a Phoenix from a flame, this classic meeting of the robotic minds returned to San Mateo, CA this year.

32 VEX Worlds 2015

by R. Steven Rainwater Highlights of this STEM inspired event.

38 How I Came to Design Extraterrestrial Robot Submarines

by Ralph Lorenz Part 2: Sailing Ligeia, Diving Kraken.

When the TiME mission proposal was not chosen, then NASA suspended the ASRG program in 2013, all seemed lost. However, new opportunities presented themselves on the concept of an autonomous sub.

PAGE 45

45 Animatronics for the Do-It-Yourselfer

by Steve Koci This new series of articles will explore the many methods, materials, and innovative new ideas to bring your robotic creations to life.

51 littleBits and the ActoBitty

by Dave Prochnow Magnets and aluminum combine to create ActoBits.

54 CNC Part Creation Workflow

by Michael Simpson This mini series will break down procedures and approaches to create consistent parts using a CNC machine.

62 The Basics of Soldering

by Bob Wettermann and Nick Brucks The final installment in this series covers advanced SMT package soldering.

SERVO 06.2015

5

Mind / Iron

by Bryan Bergeron, Editor ª

Disposable Drones When I made my first foray into the world of quadcopter drones, the cost of entry for a DYI drone was a little over $1,500. There was the nine-channel controller and receiver ($350), the quad structure ($100), the four motors ($200), microcontroller with sensors ($400), motor controllers ($180), and a good supply of lithium batteries and charger ($300). Commercial options were both limited and at least double the price. Then, came offerings from the likes of Parrot with their $300 drone, and affordable kits such as the $600 Parallax quadcopter — which required an R/C radio, batteries, and charger for a complete drone.

Today, anyone can pick up a miniature drone on Amazon for less than $30 — complete with R/C unit, battery, and charger. There’s no way I could create something that small and functional for less than ten times that — the batteries alone are $6.

I think that drones are the quartz watches of the 1970s. Through mass production and universal appeal, the price of quartz watches dropped so low that it was often cheaper to buy a new watch than to have the battery replaced.

What would be the value proposition of disposable drones? For starters, consider the delivery service. One-way delivery is the norm for most services today. That is, Amazon or other online retailers send you a box through UPS or FedEx, you open the box, remove the contents, and toss the box in the trash.

You don’t have to return the empty box to Amazon.

Of course, there’s the issue of how to dispose of the electronic waste from used drones — especially those pesky lithium batteries. The other issue is price point. At what price does a one-way flight make sense? It depends, of course, on the contents of the flight package. It’s one thing to deliver a pizza by quadcopter and quite another to deliver an organ, drug, or piece of military equipment.

As new technologies go, the move toward disposable drones will probably start as a hybrid process where, for example, the central processing “brick” could be dropped into a mailbox and returned to the seller for use in another drone. This approach would have the advantage of minimizing waste — assuming the batteries, microcontroller, and motors could be refurbished and repeatedly sent out.

Whether or not any of these predictions come to pass, one thing for certain is that hobby-level drones are becoming more affordable by the day. As such, you can easily find a drone worthy of a teardown after you’ve managed to fly the craft into a brick wall or — my favorite — the ceiling. Good luck flying. SV

FOR THE ROBOT INNOVATOR

ERVO

Published Monthly By T & L Publications, Inc. 430 Princeland Ct., Corona, CA 92879-1300 (951) 371-8497 FAX (951) 371-3052 Webstore Only 1-800-783-4624 www.servomagazine.com Subscriptions Toll Free 1-877-525-2539 Outside US 1-818-487-4545 P.O. Box 15277, N. Hollywood, CA 91615 PUBLISHER Larry Lemieux publisher@servomagazine.com ASSOCIATE PUBLISHER/ ADVERTISING SALES Robin Lemieux robin@servomagazine.com EDITOR Bryan Bergeron techedit-servo@yahoo.com VP of OPERATIONS Vern Graner vern@servomagazine.com CONTRIBUTING EDITORS Tom Carroll Kevin Berry Dennis Clark R. Steven Rainwater Bryce Woolley Evan Woolley Ralph Lorenz Camp Peavy Steve Koci Michael Simpson Bob Wettermann Nick Brucks Dave Prochnow Pete Smith Mike Jeffries Nate Franklin CIRCULATION DEPARTMENT subscribe@servomagazine.com WEB CONTENT Michael Kaudze website@servomagazine.com WEBSTORE MARKETING Brian Kirkpatrick sales@servomagazine.com WEBSTORE MANAGER Sean Lemieux ADMINISTRATIVE STAFF Debbie Stauffacher Re Gandara Copyright 2015 by T & L Publications, Inc. All Rights Reserved All advertising is subject to publisher’s approval.

We are not responsible for mistakes, misprints, or typographical errors. SERVO Magazine assumes no responsibility for the availability or condition of advertised items or for the honesty of the advertiser. The publisher makes no claims for the legality of any item advertised in SERVO. This is the sole responsibility of the advertiser. Advertisers and their agencies agree to indemnify and protect the publisher from any and all claims, action, or expense arising from advertising placed in SERVO. Please send all editorial correspondence, UPS, overnight mail, and artwork to: 430 Princeland Court, Corona, CA 92879.

Printed in the USA on SFI & FSC stock.

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SERVO 06.2015

EVENTS JUNE

Know of any robot competitions I’ve missed? Is your local school or robot group planning a contest? Send an email to steve@ncc.com and tell me about it. Be sure to include the date and location of your contest. If you have a website with contest info, send along the URL as well, so we can tell everyone else about it. For last-minute updates and changes, you can always find the most recent version of the Robot Competition FAQ at Robots.net: http://robots.net/rcfaq.html.

— R. Steven Rainwater

5-8

AUVS International Ground Robotics Competition Rochester, MI Autonomous robots built by university teams must navigate an outdoor obstacle course. www.igvc.org

6

Clash of the Bots Schiele Museum, Gastonia, NC Remote-controlled vehicle destruction. www.carolinacombat.com

6

Concurso Robotica Radio Servicio Aguilar Tapachula, Chiapas, Mexico Events include line following, labyrinth solving, mini Sumo, and robot arm. http://electronica-aguilar.blogspot.com

8-13

NASA Sample Return Robot Challenge Worcester Polytechnic Institute, Worcester, MA Planetary rover style autonomous robots built by university teams must navigate unknown terrain, avoid obstacles, and return with a sample. http://challenge.wpi.edu

13-14

Robotic Day Prague, Czech Republic Events include Bear rescue, Ketchup House, line following, mini Sumo, and Robocarts. www.roboticday.org

20

SparkFun Autonomous Vehicle Competition SparkFun HQ, Niwot, CO Autonomous air and ground robots compete in SparkFun's annual event. http://avc.sparkfun.com

25-27

MATE ROV Competition St. John's, Newfoundland, and Labrador, Canada University teams build underwater robots that must face a new challenge each year. www.marinetech.org

27-28

International Autonomous Vehicle Contest Reuben H. Fleet Science Center, San Diego, CA Autonomous robots must navigate around fixed obstacles. http://iaroc.org

27

UK National Micromouse Competition Birmingham, United Kingdom School teams build speedy maze-solving autonomous robots and compete for the best maze solving time. www.bcu.ac.uk/tee/events/techfest/ micromouse

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Visit AndyMark.com and view our wide selection of robot parts!

Use coupon code

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Kokomo, Indiana • www.AndyMark.com • 877-868-4770 SERVO 06.2015

7

Ask Mr. Roboto

by Dennis Clark

Our resident expert on all things robotic is merely an email away.

Tap into the sum of all human knowledge and get your questions answered here! From software algorithms to material selection, Mr. Roboto strives to meet you where you are — and what more would you expect from a complex service droid?

roboto@servomagazine.com

I

n spite of my ADHD tendencies, I do on occasion fixate on a project until it is perfected. This month marks the third article I am going to do on the 4D Systems’ uCAM II video/picture camera. In the first article, I showed code to run this camera on a Digilent MAX32 board with a (obsolete) NCK Electronics 1.8" color LCD display. (I still say it’s a pity he doesn't make that shield anymore.) I complained about the poor image quality, and wondered if it was the display or the camera. In my second article, I used a 4D Systems Picadillo, which used the Digilent bootloader and MPIDE "Arduino-ish" system syntax. Again, I complained about image quality and surmised that it must be the camera since two different graphics platforms had the same performance.

I was certain that this could not be the true performance of the uCAM II camera, so I dug deeper and discussed my problems with the quite responsive tech support team at 4D Systems. After testing wires, interference, and various baud rates, it became apparent that the problem was with baud rate error compatibilities between the PIC32/MPIDE compiler environment and the camera.

I do not have the final confirmed “perfect” baud table for this PIC32 environment yet (I am working on it), but have confirmed that the uCAM II camera is ideally tweaked to work at a number of baud rates (some over 3 Mbps) when used with the USB/VCOM converter cable.

However, not so much with the PIC32 UART divider registers.

Meticulous (and boring) experimentation found that the Figure 1. highest reliable baud rate I can get to automatically be detected by the uCAM II is 908500 bps. That is nearly a megabit per second.

I get a decent 16-bit color image at 1.3 frames per second using a 128x128 image, and 3.6 frames per

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second using an 80x60 image.

The 1.3 fps rate is unusable in a robot for any reasonable navigation or (ahem) targeting system, but the 3.6 fps rate can be used in some projects. I tried using the eight-bit gray scale format (4.3 fps) as well, but was unable to reasonably convert the CrYCbY format to my graphics

Figure 2.

Your robotic problems solved here.

Post comments on this article at www.servomagazine.com/ index.php/magazine/article/june2015_MrRoboto.

library 565 raw color format requirements and get anything I could use. To see how well the camera performs, check out Figure 1 which is a picture of the Picadillo 128x128 image, and Figure 2 which is a picture of what the uCAM II took a picture of.

Another problem that I had with the camera (or thought that I had) was I believed that I could only get the camera to work on power-up and not after a reset.

It is confession time — Mr. Roboto didn’t think that one through very well. If the camera is busy streaming data as fast as it can to the controller and the controller stops “ACK”ing the data, the camera will get lost.

Oops. It is no wonder the uCAM II didn’t respond when the Picadillo was reset. It got out of sync and was unable to correctly respond. The 4D Systems folks recommended that I use a “FET switch” to programmatically power cycle the camera when the microcontroller wakes up to avoid this problem <head slap moment>.

I am not an experimenter that is easy to deter when it comes to a project, so I continued to polish my uCAM II camera program to work with multiple image formats and display useful debug data directly to the TFT LCD display. Listing 1 shows the gist of my manipulations, which allows the user to pick an image format and size (for raw and gray scale experiments) very simply. I had a lot of fun fiddling with this code, so I hope you enjoy hacking on it!

The source code is available at the article link.

Newest Conclusion This camera delivers acceptable image quality to microcontrollers with UART interfaces with minimal or no extra processing of the image data. If you use the smaller image size, it is possible to use the camera for more sophisticated navigational processing if you aren’t moving too fast, or if you are using a static robot that wants to interact with its environment.

Future Experiments

Listing 1. How to Change the Image Format and Size. /* * Screen = * 1 - 128x128 565 color * 2 - 80x60 565 color * 3 - 128x96 565 color * 4 - 80x60 8 bit gray scale (CrYCbY format)? */ #define _W128X128 1 #define _W80X60 2 #define _W128X96 3 #define _W80X60G 4 const int Screen = _W128X128; int dsize, mh, ml, iCode, fCode; // Select screen setups switch (Screen) { default: case _W128X128: dsize = 16384; mh = 128; ml = 128; iCode = 9; fCode = 6; break; case _W80X60: dsize = 4800; mh = 60; ml = 80; iCode = 1; fCode = 6; break; case _W128X96: dsize = 12288; mh = 96; ml = 128; iCode = 11; fCode = 6; break; case _W80X60G: dsize = 4800; mh = 60; ml = 80; iCode = 1; fCode = 3;

I’m not finished with my work, however. I am } planning on finding a way to use the image data to uint8_t INITD[6] = {0xAA,0x01,0x00,fCode,iCode,0x00}; detect motion and act on it in a future robot. I also // data format want to see if I can speed up the image capture so the data can be used more effectively in a robot. So, look for That’s all for this month. The work I did with the these in a future column. camera took up a lot of time (if not a lot of column The old days of simple sonar and IR proximity detectors space!). As usual, please send your questions and are over, my fellow robot friends. We have inexpensive and suggestions to roboto@servomagazine.com and I’ll do my sophisticated tools to use these days, and Mr. Roboto wants best to answer! Until next month, keep on innovating and to learn and show how to use them! experimenting!! SV SERVO 06.2015

9

NEW PRODUCTS SmartScope

L

ab Nation has introduced the SmartScope: a lab device that runs on OS X, Linux, Windows, Android, and iOS (jailbroken). SmartScope balances the increased mobility of being completely powered by a tablet, phone, or PC, and being free from heavy batteries or an electrical outlet.

The SmartScope offers superior performance in its class with: • Two Analog Channels at 100 MSa/sec with 4 Meg of memory and >200 Waveforms per second.

• Eight Channels of Logic Analysis at 100 MSa/sec.

• One ARB Waveform Output Channel at 50 MSa/sec.

• Four Digital Output Channels at 100 MSa/sec.

• Trigger Out to allow for combining two units to Double Channels.

The Smartscope, in addition to the technical specification, is also an open platform allowing users to take control of the scope with their own custom or community applications.

Priced at $229, this product represents a great value for makers, students, and engineers.

SmartScope was conceptualized by the idea that today

we all carry devices that can provide displays, computations, control, and power. As a result, we do not need to put these components into instruments, therefore saving money and weight.

SmartScope was funded by KickStarter with over 1,400 Funders. These supporters have received their initial units and are actively involved in the development of applications.

Lab Nation relies on this community of users to guide projects, provide critical input to the designs, and act as advocates to the broader community.

For further information, please contact:

Lab Nation

www.lab-nation.com

Better Way from Breadboard to Protoboard

S

chmartboard introduces new bread/protoboards.

These boards are the exact dimensions of a 400 or 830 tie point breadboard with all of the same traces and power rails.

The act of taking a circuit from a breadboard and transferring it to a protoboard can be frustrating and problematic. With this new board, users can either remove the parts from a standard breadboard one at a time (while they are next to each other to assure proper placement) and solder them onto the bread/protoboard, or they can lay the new board on top of their own breadboard, place the parts through the bread/protoboard and into their breadboard.

Then, when ready, the components can be soldered from the top to the bread/protoboard, before removing it and component leads from their breadboard, thus saving the step of transferring the components from

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the breadboard to the new Schmartboard (where errors are most commonly made).

The 830 tie point bread/ protoboard (bundled with a matching breadboard) is $15. The 400 tie point bread/protoboard is $10.

For further information, please contact:

SchmartBoard

www.schmart board.com

GREAT DEALS!

FLEXY Strands

3

Doodler presents their new FLEXY line which are strands of plastic you can squeeze, stretch, and twist while designing new creations, providing a truly dynamic 3Doodler experience.

Available in five shades, this medley of malleable color can help propel your creativity into new dimensions. Packs are priced around $12.

For further information, please contact:

3Doodler

http://the3doodler .com/flexy/

Is your product innovative, less expensive, more functional, or just plain cool? If you have a new product that you would like us to run in our New Products section, please email a short description (300-500 words) and a photo of your product to: newproducts@servomagazine.com

Did You Know ...

Preferred Subscribers get access to all digital back issues of

SERVO Magazine for free?

Call for details

1-877525-2539 or go to

www.servo magazine.com SERVO 06.2015

11

bots

IN BRIEF

MOVE OVER, MILLION DOLLAR MAN

R

obotic ants the size of a human hand that work together could be the future of factory production systems.

The developers â&#x20AC;&#x201D; German technology firm, Festo â&#x20AC;&#x201D; say it's not just the unusual anatomy of real world ants that inspired the bionic version; the collective intelligence of an ant colony was also something they wanted to replicate.

The bionic ants cooperate and coordinate their actions and movements to achieve a common goal, in much the same way individual ants complete tasks for the whole colony. Festo says that in the future, production systems will be based on intelligent individual components that adjust themselves to different production demands by communicating with each other.

As reported by Amy Pollock of Reuters.

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The ants are able to complete complex tasks (like transporting large heavy loads) by working together that they wouldn't be able to achieve individually.

The robot features a stereo camera and a floor sensor that together allow the ant to work out its location and identify objects to be grabbed by grippers at the front of its "head." The antennae double up as chargers for the lithium batteries that power the ant's movements. A radio module in the abdomen allows the ants to communicate with each other wirelessly. Just like their natural counterparts, the ants have six articulated legs.

Festo says the way the ants are constructed is unique too. The bodies of the bionic ants are made from a 3D printed plastic powder, melted layer by layer with a laser. The circuitry is also 3D printed on top of the body. Festo says this is the first time these techniques have been combined.

The ceramic legs and pincers are flexible actuators that move quickly and precisely without using much energy. Again, Festo says the application of this so-called 'piezo' technology to miniature robots like its bionic ants is a first.

The bionic ants are part of the developer's Bionic Learning Network. Festo works on transferring natural phenomena to engineering techniques and equipment.

The technology firm says the factories of the future will have to produce customized products, meaning that they will have to adapt to different production requirements.

bots

IN BRIEF YOU’RE SO CADDY

T

he CaddyTrek is a smart robotic golf caddy that carries your bag so you don’t have to. The CaddyTrek allows golfers to walk hands-free, allowing players to enjoy the health benefits of the game of golf without the burden of carrying a bag.

Less fatigue means better levels of concentration and control when driving to the tee or playing the short game. Studies show that walking improves stamina and core strength, and is beneficial to overall fitness in burning calories and building muscle tone. For players who hesitate in walking their round, the CaddyTrek provides a solution to the challenge of managing your gear. Now, you can just focus on the game.

A rechargeable lithiumion battery allows golfers a playtime of 27 holes or more on a single charge. The battery charger plugs into a normal household outlet for quick recharging, and the folding frame makes for easy storage and transport. Players can store the CaddyTrek in the trunk of their car.

The CaddyTrek gives players options with its multi-mode handset. Players can operate the unit in remote, follow, or use it like a manual push cart. In remote, golfers can send the unit on to the next tee up to a range of 150 yards and at a top speed of 4 mph (or 6.5 kmh). When the player attaches the handset to his waistline and initiates follow mode, the

SWASHBUCKLING BOT

U

sing a pair of high speed cameras working to give the arm stereo vision, this robot is able to recognize the position and movements of a human “fencing”opponent, as well as its own sword. Once the human starts to attack, the robot uses custom algorithms to calculate the possible trajectories of its opponent’s sword, and then plots an

unit remains at a distance of six paces behind the player, adjusting to the pace of the player’s stride.

The CaddyTrek comes with everything the golfer needs to start playing right out of the box. Included with the CaddyTrek are the following: 1x – 24L Lithium-Ion Battery 1x – Battery Charger 1x – Handset Remote 1x – Handset Battery 1x – One year of service and support (Don’t ya just want to rush out and and get one?!)

effective defensive motion to protect itself using its own weapon.

The robot was built by Japan’s Namiki Laboratory.

Here’s what they say about the sword-fighting robot that’s controlled by high speed vision: “... We propose a sword-fighting robot system controlled by a stereo high speed vision system as an example of humanrobot dynamic interaction systems. The developed robot system recognizes both of the positions of a human player and that of the sword grasped by the robot hand. It detects the moment when the human starts to move by using ChangeFinder, which is a method of detecting the turning points.”

“Next, it predicts the possible trajectories of the sword of the human player by a least-squares method from the moment when the attack started. Finally, it judges the kinds of attack and generates an appropriate defensive motion. Experimental results verify the effectiveness of the proposed algorithm.”

We’re just really glad the swords are made of foam.

SERVO 06.2015

13

NET RESULTS

F

unded by a South Korean defense research institute, a group of roboticists at the Korea Advanced Institute of Science and Technology (KAIST) has been testing out ways of using autonomous unmanned aerial vehicles (UAVs) to locate, intercept, and disable other UAVs. Dr. David Shim, who leads KAIST’s Unmanned System Research Group (USRG) and also the Center of Field Robotics for Innovation, Exploration aNd Defense (C-FRIEND), explains what prompted this sort of research and testing: “We imagined in the near future there would be UAVs fighting UAVs. […] As found in many cases, including the recent incident of [a DJI Phantom] wandering into the White House, even if you know UAVs are out there, it is very hard to stop them. One can try to shoot them with rifles or missiles, but they are too small for guns or guided weapons. So, our solution is to stop them with another UAV. As they say, eye for eye, and tooth for tooth.”

Shim and his group are working with a variety of UAVs with Image: courtesy of KAIST USRG. different capabilities. These include agile multi-rotor UAVs equipped with nets that can be dropped on enemy UAVs to disable them. He says the biggest challenge is in programming the drones to operate fully autonomously, using onboard vision to detect the target UAVs, and then bringing them down by precisely releasing the nets on them.

The goal of the project — which is still in its early stages — is developing UAVs that could be used as part of an anti-drone defense system, and that could also go on the offensive if necessary. For a recent demonstration, Shim envisioned a scenario in which his UAVs must take on a rocket-launching enemy vehicle, which is itself guarded by its own UAVs. For the test, the first UAV to take off was a fixed-wing “eye-in-the-sky” reconnaissance drone used to gather intel on the enemy. Next, a swarm of small agile UAVs took to the sky. These small UAVs had two tasks to perform: neutralizing the guard UAVs; and escort a larger attack UAV (which in a real conflict would transport a small ground robot with an explosive charge).

ROBOTS DO DARPA

D

ARPA (Defense Advanced Research Projects Agency) recently released the final rules document for their Robotic Challenge Finals. Here is the list of tasks that robots will have to complete to score points:

1. Drive the vehicle (same vehicle type as in Trials).

2. Egress from the vehicle (get out of the vehicle).

3. Open door and travel through opening. The door will open inward (away from the robot). The door will not include a threshold. Once fully opened, the door is designed to remain open.

4. Open valve (similar to one of the three valves in Trials). DARPA will use a circular handle with a diameter between four inches (10 cm) and 16 inches (40 cm). The valve opens by counter-clockwise rotation.

5. Use a cutting tool to cut a hole in a wall (similar to one of the two tools and the wall in Trials). A circle will be drawn on the wall, approximately eight inches (20 cm) in diameter. The cutting operation must entirely remove all wall material from the designated circle.

6. Surprise manipulation task (not disclosed until Finals). The task will require manipulation and no mobility.

7. Traverse rubble. Either cross a debris field (by moving the debris or traversing it, similar to Trials) or negotiate irregular terrain (similar to Trials).

8. Climb stairs (fewer steps and less steep than in Trials). The stairway has a rail on the left side and no rail on the right side.

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FLOWER POWER

N

euroFlowers are a set of interactive solar-powered digital flowers that respond to your brain activity. The biofeedback-based art piece uses an EEG headset to read electrical currents from the surface of your head to determine different mental states. It then uses that information to guide the behavior of illumino-kinetic robotic flowers, opening the petals and changing their colors. NeuroFlowers creator, Ashley Newton is a robot fan and studied cognitive science. She says the project was designed to help externalize internal brain states.

“NeuroFlowers is an interactive art on a science installation that enables people to visualize their mental state through controlling robotic flowers with their mind.

NeuroFlowers is [a] pretty tangible example of creating your own reality in that you — either by trying to be very focused or really relaxing your mind and body — are able to make something happen in the physical world.”

She adds, “I do think that the more you’re able to be aware of your mind and control it appropriately, the more effective you’ll be at doing whatever you want and the better you’ll feel.”

With NeuroFlowers, the internal becomes external. The mind becomes tangible, shareable. If you think you want to learn more, go to https://neighborland.com/ideas/sf-neuroflowers-illumino-k.

GET HOSED

P

roperly caring for your lawn can help beautify any home (well, most any home). Droplet Robotics makes that task easier with a smart sprinkler that combines the latest technology in robotics, cloud computing, and connected services to care for plants while saving water.

This six pound robot can sprinkle water up 30 feet away, and gathers data from over 10,000 weather stations, millions of soil samples, and comprehensive biological information to make intelligent decisions on when, where, and how much water to deliver. It’s available on Amazon for $299.

Continued on page 61

SERVO 06.2015

15

Post comments on this section and find any associated files and/or downloads at www. servomagazine.com/index.php /magazine/article/june2015 _CombatZone.

Featured This Month: 16 The Influence of Combat Robot Kits

by Nate Franklin

19 Skill Building — Drive Better

by Michael Jeffries

21 Quality Versus Quantity — Or, Why One Axle is Sometimes Better Than Two

by Pete Smith

21 Cartoon

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SERVO 06.2015

The Influence of Combat Robot Kits ● by Nate Franklin

I

two drive motor gearboxes, a weapon f you go to any robot combat motor gearbox, a blade, and a special event, you are bound to see at hub made to secure the blade to the least one robot that comes from a motor shaft. kit. Whether they’re a ready to run VDD kits proved to be popular robot or a do-it-yourself package, with builders at the time. Some these kits have allowed new builders people didn’t use the entire kit, but to enter into the sport, and teach used the blades and motors. What valuable skills about maintaining a made the kit unique was that it robot.

While there were several early attempts to make starter packages for combat robots, two of the most famous combat robot kits included the VDD kit and the Battlekit.

While not really a beginner’s or complete kit, the VDD (Vertical Disc of Destruction) kits were created

by Ted Shimoda after the success of the Antweight robot of the same name. The kit came with carbon fiber rods, rubber CA glue, and kevlar thread to make a VDD, the basis for the kit of the same name.

Photo courtesy of The Robot Marketplace. frame. In addition, it included

wasn’t just a single design. The open-endedness of the frame allowed builders to create different shapes for their robots.

Battlekits were based off of Carlo Bertocchini’s successful Heavyweight robot, Biohazard.

Not just designed for combat robots, there were lightweight, middleweight, and heavyweight frames complete with independent drivetrain modules and pre-drilled mounts for motors and speed controllers.

The kits weren’t very popular, but were notable for being the only kit for the heavier weight classes.

For the 3 lb Beetleweight class, Pete Smith of Team Rolling Thunder’s Kitbots has proven to be the most dominant force. The Kitbots are based off of his bots, Pure Dead Brilliant (a horizontal undercutter), Trilobite (a brick with interchangeable wedges), and the most popular, Weta (a beater/drum spinner). Kitbots also has an Antweight kit called Saifu — a scaled down Weta designed to have a spinning drum with internal motor.

The inspiration to produce kits came from his Nutstrip material used in his bots at the time.The Nutstrip allowed him to build bots easier and make them able to stand up to the competition.

Pete ended up selling kits after being asked to make some for a local school.

When it comes to his kits, Pete says, ”When I design a kit, I focus on three things. Firstly, it has to be competitive. Secondly, it has to be relatively easy to build and repair, and thirdly, it has to be affordable. I build and compete with prototypes, tweak the design as required, and then offer it as a kit or as a completely built up turnkey bot.”

A lightweight Battlekit.

Photo courtesy of Battlekits.com.

Pete Smith with Trilobite, the basis for one of his Beetleweight kits.

Photo courtesy of Pete Smith.

Nutstrip of different sizes, with a quarter for comparison.

Photo courtesy of Kitbots.com.

Kitbots have given many inexperienced competitors the edge at events when it comes to competing, and the parts are easy to replace and be integrated into new designs. Pete also feels that his kits have changed

Several Kitbots at an event.

the way the weight classes have evolved. Builders end up making their bots more deadly in order to take down the tried and tested Kitbot designs.

Meanwhile, FingerTech Robotics has put its own kit into the market.

For the Antweight class, the Viper Kit has become a go-to choice for new builders. Kurtis Wanner, the owner of FingerTech Robotics, wanted to make it easier for new builders to get started in the sport of robot combat.

“Ten years ago, it was incredibly difficult to get started in combat robots.

There weren’t yet any stores dedicated to designing and manufacturing parts specifically for small combat robots, so builders were stuck with what they could find at the local hobby stores — parts that were normally meant for R/C cars and airplanes. I saw an opportunity to help grow the sport by supplying a kit of SERVO 06.2015

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Kurtis Wanner with Viper kits (from left to right): Kitbot, a modified Viper kit; Lift; and Spin. Photo courtesy of Kurtis Wanner.

parts that eliminated all the guesswork.”

Ten years ago, he decided to throw his hat into the ring. “The very first kit consisted of a 75 MHz Hitec Ranger III radio, two Tamiya HP gearboxes with plastic sport tires, a Scorpion ESC, and a 7.4V LiPo battery.

(Materials were up to the builder.)

There was still a lot of work to be done, but at least the builder knew they weren’t wasting money on parts that may not work well together.

“Over the years, the hobby store parts were replaced one at a time by custom designed FingerTech parts: Spark motors, tinyESCs, Lite Hubs, and custom “Viper” chassis and armor.

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This year, we released the new Viper V2 kit that Zachary Lytle with a young builder holding incorporates things we both of the kits he designed.

Photo courtesy of Zachary Lytle. learned over the five years of V1 sales. Stronger around 200 builders. I like to think chassis and armor to deal with today’s that means that 200 new builders deadlier spinners, Snap wheels and were able to join and compete in hubs, quick disconnect terminal blocks combat robot events around the and motor wires for people who country. At our local SCRC Kilobots aren’t adept at soldering (even if you events, I used to watch as new are, it’s nice not to have to do it builders would be discouraged during an event!), and optional lifter because their robot did poorly. Now and spinner add-ons for builders who want to upgrade their robots from the with the Viper kit, they can be competitive right out of the gate. This basic wedge design.” has led to a higher builder retention Over the years, Pete has seen a positive change in the sport, as he rate, and the Viper can be used as a stepping stone to new designs.” states, ”The original Viper kit sold to Zachary Lytle of Team Misfit is selling a kit of his own design through FingerTech Robotics. Running a party service called “Bot Bash” where kids of all ages can drive robots, he got a lot of parents and children asking how to get started.

This led to Zachary writing a SERVO article in the October 2012 issue detailing step-by-step instructions on how to make a simple The RRevo kit. wedge Antweight (1 lb) Photo courtesy of RRevo.com. robot. He followed up with a second article in the April

2013 issue detailing how to make a lifting or clamping robot.

With the help of FingerTech robotics, these kits became available for dedicated builders to purchase and get started. For Zachary, it has been a rewarding experience, as he has seen young builders get into the sport with his kits and have the time of their lives. He says, “Seeing kids enjoying robotics makes all the hard work and frustration of developing a kit well worth it.”

Insect class robots aren’t the only place you’ll find kits. RRevo (Robot Revolution) has recently spawned a 15 lb kit designed by Bradley Hanstad.

Hanstad is no stranger to combat robot kits, as he started out with the aforementioned VDD kit.

His kits were made due to the demand for an educational robot combat league in southern California.

The starter kit includes a water jet aluminum frame, an ESC for its two motors, LiPo batteries, and wheels.

After that, it’s up to the builder as to what modifications they should make to the robot.

Bradley’s design philosophy in regards to the kit is, “The reason I built out these kits was to give a cheaper starting kit that offered far better parts than anything on the market. It is a full kit with everything you need to run a robot, and it offers some overkill in the right spots to make it easy and safe for beginners, but at the same time offers some modular design to adapt it to your personal design without the kit being overkill and too strong. I firmly believe a kit should never be sold if it is too strong of a robot to begin with.

Otherwise, you lose the point of the sport of combat robotics which is

www.robotcombat.com/products/ battlekits.html www.kitbots.com www.fingertechrobotics.com http://botbashparty.com/ over-drive www.rrevo.com learning and building your own.”

Bradley’s kits have been used by many different schools in California.

He hopes this will help the sport grow and help kids learn more about mechanical engineering.

While kits may not be for everyone, it’s clear that they’ve played a huge part in the growth of the sport, and will continue to do so for years to come. SV

Skill Building — Drive Better ● by Michael Jeffries

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and drive it as much as possible point where you’re thinking about obot combat is a sport with before the first event, as well as what you need to do with the extreme design diversity. You’ll between events.

A large element to controller and getting to the point see spinners, flippers, axes, driving well is moving beyond the where you’re thinking about what you crushers, pushers, and a range of want the bot to do. other things constantly pushing the limits of what’s Here are a few techniques safe and what’s legal to run at that can augment basic driving an event. In many ways, it’s practice and help you get up like an elaborate game of rockto speed. paper-scissors.

Barring some of the more elaborate mechanisms and designs, the rock, paper, and Basic driving practice is scissors all share a common nice, but there’s a lot more to element. They all need to be being a good driver than just driven. Good driving can make driving your bot around alone. a simple robot look great, and In robot combat, you’ve got poor driving can make a another bot in there with you. beautifully designed robot a Just driving the bot can get flop. you used to how the bot Figure 1. A basic test area for use with relatively The best way to start on drives, but chasing a live — safe weapon systems. This test area was built using a the path to becoming a good often erratic — target gets you pallet, some plywood, and about 16 feet of 2" steel angle brackets. driver is to finish your bot early ready for combat.

Target Practice

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and cheaper, one of my whatever materials you’d like, so long favorite driving practice as they’re sufficiently thick and well games is “Kill the Weazel mounted to handle the damage your ball.” To play the game, get machine is capable of. a Weazel ball (or a generic Plywood is a great option for knockoff — it really doesn’t areas you don’t need to see through, matter) and remove the as it’s cheap and can be bought in a tail. Once the tail is gone, range of thicknesses. For areas you you turn the ball on and need to see through, polycarbonate is put it in the test area. The the option to go with. Insects can get goal is now to turn off the away with fairly thin polycarbonate ball or pop the shell off. panels for a test box since you’re Again, do this in match trying to ensure it doesn’t let shrapnel length increments for more escape, but aren’t concerned with it accurate practice. taking the worst hits possible and still The standard Weazel being usable. ball is best suited to When selecting materials, Figure 2. A de-tailed Weazel ball makes a practice for 150 g to 3 lb remember that for Insect bots many great target when you're practicing solo. robots. In testing, I’ve arenas use 1/4” polycarbonate, and found that kinetic impacts for larger bots 1/2” and 1” from 1 lb spinners can be polycarbonate aren’t uncommon. Be sufficient to turn the ball safe and keep the damage in the off without causing any arena. serious damage to the integrity of the ball.

One thing that is an Most radio systems and motor absolute must if you’re controllers support the use of planning to do drive testing anywhere between +100% and -100% with your weapon system throttle. Most drivers seem to use active is to ensure the 100%, 0%, and +100% almost environment is safe for it. exclusively.

In the case of lifters and This is not ideal. Driving like this grabbers, this isn’t a huge tends to result in a robot wildly racing issue, as they’re typically no Figure 3. A test box capable of handling spinning across the arena and slamming nose more dangerous than the weapons needs walls and a roof. robot as a If you can find someone to assist whole. When you start you, a classic option is to have them dealing with axes and pilot a cheap remote controlled car. flippers, you begin to They try to get away; you try to break either need an the car (hence, the cheap part); and enclosure to test in or the chase goes on for approximately a substantial amount three minutes at a time. Practicing in of distance between match length intervals will get you you and the practice ready for timed combat matches. If area. With high you haven’t gotten it done in three powered spinning minutes, you won’t have time to get it weapons, a test box is done. a must.

When practicing with this The key things method, it’s useful to have a test area with the test box are that is similar in size and surface to that the walls and roof the arena you’ll be fighting in. It’s not must be able to necessary, but it helps. contain your weapon If you don’t have a willing victim system. This can be Figure 4. There's a full range of travel to use. or would just prefer something smaller achieved with

Throttle Control

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first into the wall. Taking the time and learning how to use the full range of travel (either using linear or exponential settings) will result in being able to drive much more smoothly. Smooth driving is controlled driving, and controlled driving gives you an advantage.

I prefer fast bots. The bots I run at events are usually some of the fastest machines in the class. Most of

the time, I’m not using nearly all of that speed. I spend most of my time in matches below 50% throttle, only going to the limits of the travel when I’m lined up for or trying to avoid an attack. That being said, when fights I’m in go to the judges, I tend to score highly on aggression.

So, why would the bot that’s driving slower and in a more controlled manner score high on

aggression? It’s simple: Aggression isn’t the fastest bot. It’s not the bot that’s constantly charging in the general direction of their opponent.

Aggression is the bot making successful attacks on their opponent.

Blasting past your opponent and into the wall just gives them a free shot.

Speed is great. Accuracy is better.

SV

Quality Versus Quantity — Or, Why One Axle is Sometimes Better Than Two ● by Pete Smith

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he drums on my Saifu kits have worked pretty well, but when they lose it’s usually been the same problem: bent axles. The drum uses a shoulder screw as a live axle at one end and the shaft of the Outrunner itself at the other (Figure 1). Initially, I used a 3/16” shoulder screw and that would be the failure point. I fixed that by moving to a 1/4” shoulder screw, but then the weak

point was the 1/8” diameter axle in the Outrunner. A big hit would bend that small shaft and the motor would then seize up.

The existing design was simple to build as the entire motor would be glued into the drum, but it was clear that a tougher solution was required.

First thoughts were to replace the motor shaft with a tougher one. A customer tried a titanium shaft, but

that did no better; my next thought was to use a custom hardened steel one. This may have worked, but hardening steel is a complex subject and getting the right blend of hardness and toughness could have been tricky. I had also been considering another solution for some time.

This would have been to take the motor apart and use a much bigger SERVO 06.2015

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Figure 1. Old style drum.

Figure 2. Algos.

Figure 3. Cross-section.

Figure 4. CAD version of the drum assembly.

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I used SolidWorks 2005 to design the various parts. A crosssection of the final design can be seen in Figure 3. The axle (in light blue) is located in the chassis by the stator (in light green) on the right and a flanged bushing on the left.

It should be noted Figure 5. Bearing. that this is a “dead” axle; it does not rotate with the drum. The bushing on the left is only required to locate the 1/4” grade 5 titanium axle in an existing larger hole in the chassis. Two flanged ball bearings (in pink) allow the drum to spin freely on the shaft, and shims and washers keep the drum axially positioned Figure 6. Mangled motors. relative to the stator.

The rotor (In beige) is glued into one end of the drum. Otherwise, the diameter dead axle and drum is much as before (Figure 4), separate — much bigger with two teeth on each side and slots — ball bearings to milled to allow easy removal and mount the drum and replacement of the rotor if necessary. the rotor (the part of One advantage of the new design is the motor that has the permanent magnets). that because no clearance is required The stator (the part for the bell housing on the motor, the with the teeth can be a little further apart — 1” electromagnets) would rather than 0.7”. remain mounted to the My first task was to dismantle the Turnigy 28-22 Outrunner motor. The chassis. The tricky part would bell housing and shaft are secured to be to ensure that the rotor the stator with a tiny circlip on the remained concentric with the shaft. stator, and that the permanent While it might be possible to get and electro magnets were still a special set of pliers to remove this aligned correctly. clip in one piece, it’s not needed in What finally spurred me the final assembly.

So, I bent it apart into action was Mike Jeffries’ with a small flat blade screwdriver and successful implementation of a removed the remains with a pair of very similar design in his Antweight, Algos (Figure 2) fine-nosed pliers.

The stator has two small ball which took first place at bearings pressed into it (Figure 5) Motorama this year.

which need to be removed.

I practiced this on an older slightly different motor first and they popped out right away, but the ones on my chosen motor proved unwilling to come out so easily. I used a small hammer and a blunt nosed punch. That got the bigger one out, but I had to (carefully) use my drill press to get out the other one.

Figure 8. Rotor.

It’s easy to damage the soft aluminum of the stator housing, and I mangled two motors before finally succeeding (Figure 6).

Figure 7. Removing the bell housing.

The bore left between the two bearings was almost exactly 1/4” in the trial motor but slightly less in the one I finally used. I drilled it out to 1/4” in steps to ensure it would be a nice close — but sliding — fit on the axle. Too loose and the stator and rotor would no longer be concentric; too tight and Figure 9. Machining a recess for the rotor. the axle would be hard to fit and remove for servicing.

I removed the bell housing and the old 1/8” axle from the rotor by lightly clamping it in the jaws on my lathe and machining it carefully (Figure 7) until the two parts separated, leaving the rotor as a separate ring (Figure 8).

The drum itself is 7075 aluminum. Figure 10. Counter bore for the bearing flange.

I turned the exterior down to a diameter of 1.7”, drilled out the center with a 15/32” drill, and then the part over and used that flat reamed it out to 0.500” (the size of to orient the drum to allow a the outside diameter of the ball matching flat to be machined bearings). opposite it. The part is then The next step was to machine the turned 90°, and the two flats recess for the rotor using a boring bar align the part in the vise so that (Figure 9). flats can be added at 90° to the This needs to be a close sliding fit first set.

Figure 11. Machining flats. for the rotor. A small recess (Figure A vise stop and edge finder 10) for the flanges on the bearings (Figure 12) together with the was then added to each end of the DRO on my mill made positioning and drum to get the weight down to 1/2”. To ensure the features on the milling out the teeth mounting holes about 4 oz (Figure 13). outside of the drum are all correctly and the slots to allow the rotor to be I chose flanged bearings (Figure oriented on top of each other, I levered out a quick and easy task. The 14; McMaster part# 57155K323) to machined a flat on one side of the last major machining job was to make it easy to limit how far they get drum (Figure 11), and then flipped remove enough material from the pressed into the bore. I then chose SERVO 06.2015

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should have been an easy sliding fit, I decided to try another of the bearings and it slid right on!

I had bought four bearings, and all the rest fit the shaft without problems. The lesson to learn is do Figure 12. Use a vise stop and edge finder.

Figure 13. Losing weight. not assume that if a bearing won’t fit, that all similar bearings won’t fit.

I measured the shaft and it was not oversized, so I should have guessed earlier that the problem was with that particular bearing and not the shaft.

The bearings were a light press-fit in the bore, and the rotor was Figure 15. Pressed-in bearing and glued rotor. secured in place using a smear of “Goop” adhesive Figure 14. Flanged ball bearing.

(Figure 15). The stator side of the motor is screwed to the side wall of the chassis (Figure 16).

It is important to ensure that none of the screws hit the wires going into the motor or the coils on the magnets themselves.

I used small nylon washers to space the screws out to accomplish this, adding two Figure 17. Shims washers under two of the on the axle. screws and one under the other two. applications are so outside normal I assembled the drum onto the use that establishing a relationship axle and added a number of shims Figure 16. between dynamic load ratings and (Figure 17) to maintain the correct Stator mounted on the chassis. actual effectiveness for any weight axial position of the rotor relative to class in combat robotics would be the stator. I found that two shims very difficult. resulted in a gap between the stator shielded bearings since they protect The first bearing I tried did not fit and rotor similar to that of the original against dust, etc., getting into the onto the 1/4” titanium shaft, and it motor. bearings without the drag of a fully was still a press-fit on the shaft even The next task was to balance the sealed bearing. I also checked that the after I de-burred the shaft and gave it drum assembly. I mounted it on the speed rating exceeded the likely max a quick sanding on the lathe. axle and supported the axle on two RPM of the drum.

Given that the ground titanium sockets of the same height. The The dynamic load rating of 243 shaft was supposed to be just under shielded bearings allow the drum to lbs seems adequate, but our 1/4” (and the bearing just over) and rotate freely, and the heavy side will

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always settle at the bottom. I must have made a machining error when I was lightening it as it took drilling a large “divot” out of that heavy side to get it to balance properly and not settle repeatedly at any one point (Figure 18).

Figure 18. Balancing the drum.

This results in static balancing only, but because the part is symmetrical around the axis of the axle, it is usually good enough for our purposes.

The drum was assembled back into the chassis and the axle secured at each end with a washer and a cotter pin (Figure 19).

I then tested the drum by hooking up the electronics of my wide Figure 20. Testing the drum. version of Saifu to the stator in the new chassis (Figure 20) and it spun up smoothly California at the time of this writing. with no problems at all.

My next step is to rebuild my The assembled kit was shipped wide version of Saifu with a similar off to the customer and was built up drum and compete at this summer’s as the Antweight, Hopeful Narwhal “Clash of the Bots.” Then, if it works (Figure 21). It competed (winning at well, I’ll make this design the basis of least one fight) at RoboGames in a new kit available to the public.

Figure 19. Washer and cotter pin.

Figure 21. Hopeful Narwhal.

I think I will also build a 3 lb version of this drum and try it out in a modified Weta chassis ... lots to do!

SV

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RoboGames 2015

By Camp Peavy with contributions by Bob Allen and Michael Mauldin

Like a Phoenix from the flame, RoboGames is back! Last year, we mourned its death, got over it, and moved on. Then, with a $45,000 Kickstarter campaign, once again robot builders from around the world gathered. In all, there were 655 competitors and thousands of robot enthusiasts who s) c i t o b enjoyed the spectacle. Of course, is. er Ro Mist for all th , . a . k . e l a ( b i ins spons most came to see the ComBots ...

Calk re Davethe guy — that is, what's left from the glory days of RobotWars and BattleBots. However, there were humanoid Kung-fu fighters; soccer robots; Sumo robots; fire fighting robots that navigated miniature houses and extinguished burning candles; table top navigation robots who survived, lived, and played on a table; RoboMagellan robots — full-scale robots roaming the earth looking for orange cones; bartending robots who solve the world's problems or at least help you to deal with them; Artbots for art's sake; musical robots (for the sound of music); LEGO robots for the juniors to play with; hexapods (just to bug you); robot painters — so robo-Gogh!; BEAMers (organic, of course); and "Best of Show" for the best of the best.

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Figure 1: My HomeBrewed menagerie, including the Black Mast Dancers (a Kinetic ArtBot entry).

Figure 2: Steven Nelson and Bill Sherman (as Doc Hadacoff) — two bedrocks of RoboGames. There's a video of Steven's Beer2D2 in the "Additional Materials" section. Doc Hadacoff took Silver in the Musical ArtBot category.

W

hen I arrived on Friday (April 3rd), the first order of business was setting up my own HomeBrewed robot menagerie, including the Black Mast Dancers (Figure 1). The first person I encountered was Steven Nelson — a RoboGames institution. Steven is always at RoboGames ... wrangling the combat arena together and generally showing off his latest creation (which is currently the spunky little Beer2D2. Watch for an upcoming SERVO article on Beer2D2 soon.) Next, I saw Bill Sherman who Figure 3: The Indonesians were real powerhouses in a variety of RoboGames events. Here, Galih runs Gold medal winning Xerok-V15 through Phase 2. hadn’t transformed into “Doc Hadacoff” yet. He had spent the night before soldering medals. He demonstrated (among other things) his BarBot Elixirator and In addition to overseeing my menagerie of his musical ArtBot Pendulum (Figure 2). A bit later, I saw HomeBrewed robots, I officiated two RoboGame events: Bill’s lovely wife, Becky who too had a full day between Table Top Nav and RoboMagellan. Friday evening was the teaching school and getting to the big game. She is the Table Top Navigation event (Figure 3). There were five Mistress of Ceremonies at the Medal Podium. entries: three Indonesian; one USA; and one German. The Many of us have been involved with RoboGames since Indonesians are a genuine powerhouse at RoboGames the beginning. It’s in our blood. RoboGames, BarBots, participating in everything from ComBots, fire fighting, Maker Faire, Robot Block Party, HomeBrew Robotics Club ... soccer, RoboMagellan, and Table Top Nav. I’ve known a few there’s always a robot-themed activity somewhere near of them for years (in particular Rodi, Taufiq, Februandi, Silicon Valley.

Galih, and Eko), and we’ve recently become Facebook Soon thereafter, I encountered someone who seemed friends (there’s that Facebook connection again). familiar but I didn’t recognize. Then, it dawned on me. This The goal of Table Top Navigation is to move a block was Gaby Dlib — a Facebook friend from Mexico. into a shoebox mounted at the end of the table. There SERVO 06.2015

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Figure 4: Savage Solder from the USA completes his impossible Gold medal run. A link to the entire run including the "Cone of Death" is in the "Additional Materials" section.

aren’t any specifications on the size of the table, the block, or the shoebox. It’s more of a show than a contest, and the judging is qualitative not quantitative; like how gymnastics routine scores are based on difficulty, artistry, and demonstration of required elements.

Technically, there are three phases: Phase 1 is simply to move from one end of the table to the other and back.

Phase 2 is to push a block off the edge of the table, and Phase 3 is to move the block into a shoebox mounted at the end of the table. While most contestants just go for Phase 3, the Indonesian teams did each phase in sequence, and in the end they swept the event. Xerok took Gold, Capit Silver, and Orangutan Bronze.

Saturday (April 4th) was the RoboMagellan event

(Figure 4). RoboMagellan is an outdoor event where contestants are given a GPS coordinate “goal” on which an orange cone is placed. The robot has to transverse a roughly 200 yard playing field with obstacles including trees, buildings, light posts, trash cans, etc., and touch the goal cone, then stop. Along the way, there are bonus cones which the contestants can elect to touch (not required) which will yield a fractional multiplier; that is, it will decrease the overall run-time score. However, if the robot does not touch the goal cone, no “timed score” is given and the score is the distance from the goal.

There were 16 entries: 14 showed up and eight were competitive, meaning they made it to within 20 yards of the goal. Four managed to actually touch the goal cone.

Entdecker by Marco Walther from Germany had two decent runs. On his last run (you’re given three), he touched bonus cone #2 (a “.5” multiplier) and ended up only four yards from the goal cone. Kybernetes from the Robotics Society at UC Merced (headed up by Nathaniel Lewis) was the most consistent: four yards from the goal on the first run; one foot away on the second run; and only one yard away from the goal on the third — using just GPS. Monty from the Palos Verdes Institute of Technology

Additional Material Video of Beer2D2 http://ilovegram.com/m/955393610754025363_10962808 RoboGames 2015 http://tinyurl.com/Headbanger142-RoboGames2015 Mechanical Olympics: RoboGames 2015 Kick-off! www.youtube.com/watch?v=VJJkECkAYNA Touro Maximus vs. Original Sin (RoboGames 2015 Heavyweight Final) www.youtube.com/watch?v=S7FkEzpJBFw Garage Robot Combat at RoboGames 2015 www.youtube.com/watch?v=TyiMnNSsq6A Savage Solder - RoboGames 2015 RoboMagellan winning run www.youtube.com/watch?v=pWeJcXutyZg Figure 5: After a very tough day, Tiago Shibata just completes his Bronze medal run.

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SACbot - RoboGames 2015 RoboMagellan - Third and smokeful run www.youtube.com/watch?v=pkt-f59BGKY&feature=youtu.be

Figure 6: The Indonesian team(s) swept Robot Fire Fighting. Rodi Hartono (center) took Gold with his fire fighter DU114-R.

Figure 7: Nick Donaldson (King of the Hexapods) and son with his Gold medal walker, Glider.

scored a goal cone on his second run, with 1:23 for the Silver medal. SACbot out of Walnut, CA touched the goal cone and bonus cone #2 on its first run for a modified time of 2:21 for fourth place. Unfortunately, that was just out of the medals, but SACbot’s third run was spectacular!

As SACbot tried to climb the curb to the “Bonus Cone of Death” (a cone that was off the map on a curbed island), there was smoke! Watch the video on YouTube. (A link is provided in the “Additional Material” section.)

The most inspiring RoboMagellan entry was ThunderWaze from Brazil (Figure 5). One member of the team in particular — Tiago Shibata — worked particularly hard having two poor runs to start. The first one barely got off the starting line. Then, on the second run, the robot went crazy running around in circles. After hours of tweaking (the event took over five hours total), on its third run ThunderWaze made a beautifully simple 100 yard dash with a less than 90 degree left turn and another 50 or so yards, and touched the goal cone in one minute 39 seconds, beating Team SACbot by 42 seconds for the Bronze medal.

It was a wonderful thing with the time, energy, and effort applied under pressure. This is what RoboGames is all about — the thrill of victory and the agony of defeat!

Finally, another veteran of RoboGames, Savage Solder did the impossible and touched the Cone of Death with its incredible “.01” multiplier (no one was supposed to be able to do this). With a real run-time of 3:04 and a multiplier of “.01,” this drove his modified time down to 1.84 seconds which has to be some kind of RoboMagellan record.

Figure 8: The always masterful Mark Setrakian took Gold in the Kinetic ArtBot event with his creepy-cool Axis.

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Figure 9: This was my favorite robot of RoboGames: Kosan-Kun by Tetsuji — a delightful drum-playing robot from Japan. He took Gold in Musical ArtBot.

Figure 10: Erin Kennedy (a.k.a., RobotGrrl) shows off her shapeshifting Rapidly Deployable Automation System earning Canada the Gold in Best of Show.

Note the magic winged headband.

sweep of the fire fighting (Figure 6).

Speaking of powerhouses, another robot builder of note managed to sweep a whole category all by himself. Nick Donaldson (the guy with a monkey on his shoulder) swept all three medals in the “Walker Challenge” for the UK. He might as well claim the title “King of the Hexapods” (Figure 7). Mark Setrakian of Industrial Light & Magic fame showed off his latest ArtBot Axis to claim the Gold medal in Kinetic ArtBot (Figure 8).

However, my favorite robot at RoboGames this year was Kosan-Kun by Tetsuji — a delightful drum-playing robot from Japan (Figure 9). I understand from Tetsuji that he Figure 11: Of course, most of the crowd came to see the combat robots ... take a look at some of the combat videos listed in the "Additional Materials" section. has an entire robot band! Finally, another RoboGames and Maker Faire institution Erin Fire fighting hosted by Bob Allen (another RoboGames Kennedy, a.k.a., RobotGrrl (inventor of RoboBrrd and the institution) started Sunday (April 5th) at noon. This year’s host of the Online Robot Party) from Canada took the top fire fighting contest had 10 entries: two teams from spot for Best of Show with her Rapidly Deployable Indonesia; two from Nevada; and three teams from Silicon Automation System (Figure 10).

Valley. The Indonesian teams had a combined entry of five This is a moonshot dream of a world where everyday competitive robots, so that set the playing field, with objects move around and adjust to our various needs; DU114–R being the most competitive this year by putting spaces that shapeshift to our commands. She demonstrated the candle out all three times. a headband which could control various robotic This Indonesian robot is one of the best, having taken components just by head movements and eventually first place in the last four years at RoboGames and this year thought patterns. The headband with its Mercurial Wings was no different. So, the battle was for second and third looked absolutely fabulous! with five of the robots only putting the candle out once in All throughout the weekend, the combat robots roared their three attempts.

(Figure 11). The Heavyweight combat class at RoboGames The time between second and third was only two onewas almost evenly divided between veteran, ranked hundreths of a second, with Zharfan taking second and competitors, and brand new fighting robots. The medals all Dendi taking third. As mentioned earlier, the Indonesians went to older more seasoned machines, however. Brazil were a powerhouse at RoboGames, also making a clean took the Gold medal with RioBotz’s Touro Maximus (Figure

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Figure 12: Touro Maximus (Brazil) throws Original Sin (USA) into the air in the Heavyweight finals.

Figure 13: Original Sin knocks Last Rites on his side for Silver in 220 lb combat ... Last Rites took Bronze.

12). Team USA took Silver with Original Sin and Bronze with Last Rites (Figure 13). The best performance by a new robot was fourth place for the USA’s Polar Vortex by Michael Mauldin. In what may be a watershed moment for the Heavyweight division, this is the first time the champion used brushless motors to power its weapon.

Touro Maximus uses two Scorpion motors to drive a single spinning drum with four rubber belts.

Perhaps the most exciting new robots were HyperBite

and Doomba — both horizontal spinners with a single gearbox and multiple brushless weapon motors. Teething problems prevented these two rookie bots from advancing to the medal rounds this year, but being able to combine three or even eight smaller motors to power a single weapon may allow for even harder hitting Heavyweights in the future. SV

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By R. Steven Rainwater

E V X W O R L D S 2015

VEX Worlds 2015 was held on April 15-18 at the Kentucky Exposition Center in Louisville, KY. I was present to photograph the events, and offer a few of my favorites here. VEX Worlds consists of five world championship robotics events: the VEX IQ Challenge for elementary and middle school students ages 8-14; the VEX Robotics Competition for middle school and high school students ages 11-18; and VEX U for University students age 18 and over.

T

his year, over 850 teams from 29 nations gathered to compete. Over 12,000 total teams from all over the world competed in more than 1,000 regional events, and the best of the best made it to VEX Worlds to find out which teams would be the new world champions. The event is sponsored by a wide range of organizations who benefit from improvements in STEM (Science, Technology, Engineering, and Mathematics) education, including the Northrop Grumman Foundation, the US Army, Chevron, EMC Corporation, NASA, Microchip, Robotmatter, Texas Instruments, Ford Motors, GE, and many others.

2015 is the first year VEX Worlds has been held in Louisville. The event has already outgrown several other venues, including Anaheim, CA; Orlando, FL; and Dallas, TX. The Kentucky Exposition Center is well-suited for the rapidly growing event and should make a good home for it over the next several years.

One aspect the participants seemed to particularly enjoy was the adjoining Kentucky Kingdom amusement park. Nothing like an evening riding roller coasters to end a weekend of robot competition! For old-timers like me, downtown Louisville offers restaurants with a fine selection of Kentucky Bourbons.

The VEX IQ Challenge program includes both an autonomous and remote-controlled robot skills competition, but the contest itself is just one part of a larger program to enhance STEM education. The students â&#x20AC;&#x201D; working together in teams â&#x20AC;&#x201D; learn a variety of skills that will help them in the real world; skills ranging from planning and engineering to research and oral presentation. For 2015, the VEX IQ

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Challenge was a game called Highrise, played on a four foot by eight foot rectangular field. An alliance of two robots must work collaboratively to move and stack colored cubes in a scoring zone.

The VEX Robotics Competition adds some complexity over VEX IQ to challenge the older students. There are similarities as well, such as the combination of autonomous and remote-controlled robot skills competition. Like VEX IQ, students are simultaneously learning valuable life skills that will be useful in STEM fields and beyond.

For 2015, the VEX Robotics Competition game was Skyrise. Played on a 12 foot by 12 foot field, a blue alliance and red alliance face each other. Each alliance is composed of two teams. The alliances must work together to assemble scoring posts into skyrises and load them with scoring cubes.

VEX U is the most complex of the events, and focuses more on a demonstration of autonomous robot skills. The university-level students must learn extensively about sensors and real time control, and are allowed more freedom in fabricating custom components for their robots.

The 2015 game for VEX U was the Skyrise game just described.

During the course of VEX Worlds, hundreds of elimination matches take place leading up to the finals on the last day of the event. Throughout the four days, there are award presentations for other VEX related topics such as the online challenges hosted by the Robotics Education & Competition Foundation throughout the year. New members are inducted into the STEM Hall of Fame during VEX Worlds, as well.

Post comments on this article at www.servomagazine.com/index.php/magazine/article/june2015_Rainwater.

The main arena.

Crowd of spectators in the main arena.

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1.

2.

3.

4.

5.

6.

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7.

8.

9.

10.

PHOTOS: 11.

12.

1. VEX IQ match.

2. One of many international VEX teams.

3. VEX IQ match.

4. Driver gets a high five.

5. Heritage Christian team.

6. Playing bean bag toss between matches.

7. Teams taking a break at the social media lounge.

8. Roses & Knights team.

9. HexBug play area.

10. VEX Robotics Competition match.

11. Eastwood Robotics team.

12. VEX U match.

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One of the world champion teams on stage during awards ceremony.

VEX IQ team receiving a trophy.

So, who won? Table 1 shows the official list of the VEX Worlds 2015 championship alliances.

There were lots of other awards given out for division winners, special judges awards, sportsmanship awards, design awards, and more.

To see a complete list of every award from VEX Worlds

2015, visit www.robotevents.com/championship /awards.

If you'd like to see more photos of the event, refer to these Flickr albums: https://flickr.com/steevithak/sets/ 72157651975896521 www.flickr.com/photos/ 131938980@N05/sets. SV

VEX IQ Challenge Elementary School Excellence Award

15B

Crescent Crazy Stackers

Crescent Elementary School

Anaheim, CA

Teamwork Champion

10512A

Nanning Jinjua Primary School

Jinhua PS A

Nanning, Nil, China

Teamwork Champion

10586A

Nanning Xiutian Primary School

Xiutian PS Team 1

Nanning, China

VEX IQ Challenge Middle School Excellence Award

8899Y

Vexecutives

Manatee County Robotics Club

Bradenton, FL

Teamwork Champion

2587X

DiscoBots - Xray

DiscoBots.org

Houston, TX

Teamwork Champion

7065A

Elementrix

Yabucoa

Yabucoa, Puerto Rico

VEX Robotics Competition Middle School Excellence Award

7700B

Rolling Robots

Rolling Robots

Rolling Hills Estates, CA

Tournament Champion

8066A

Atom

Hai Sing Catholic School

Singapore

Tournament Champion

8066C

Thor

Hai Sing Catholic School

Singapore

Tournament Champion

88193A

Shanghai Yongchang A

Shanghai Yongchang Private School

Shanghai, China

VEX Robotics Competition High School Excellence Award

2918A

GCEC A

Glenfield

Glenfield, Auckland, New Zealand

Tournament Champion

2915A

Lynfield College Robotics

Lynfield College

Auckland, New Zealand

Tournament Champion

9090C

T-VEX JAWZ

The Mandarin Chinese School

Arlington, TX

Tournament Champion

2131C

Starfox

Davis High School

Kaysville, UT

Excellence Award

AURA

Auckland Uni Robotics

Auckland University Robotics Association

Auckland City, Auckland, New Zealand

Tournament Champion

QCC2

Blue Rooster Robotics

Quinsigamond Community College

Worcester, MA

VEX IQ

Table 1.

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How I Came to Design Extraterrestrial Robot Submarines

In last month's issue, I summarized what we know about Saturn's moon, Titan, and how the amazing discoveries by the international CassiniHuygens mission over the last decade have transformed our view from a blotchy dot in the sky into a fantastically diverse Earth-like world, with vast equatorial deserts of giant organic sand dunes, and polar seas of liquified natural gas. It is a world exotic, and yet familiar. itan is an easy place to explore. Unlike Jupiter’s moon, Europa, Titan does not expose spacecraft to severe radiation which can fry electronics in days.

Also, whereas airless moons like Europa require heavy and expensive rocketry and guidance to soft-land, Titan has a giant soft cushion of an atmosphere. With simple heat shields and parachutes, it is straightforward to deliver hardware to Titan’s surface from space, and the thick atmosphere and low gravity makes Titan a much easier place to fly than Mars. While Mars’ entry and descent is sometimes called ‘six minutes of terror,’ it is more like a couple of leisurely hours on Titan. Titan’s only challenge is that it is a billion miles away!

For 20 years or more, scientists have advocated various ways to explore Titan — and there is almost no vehicle you can imagine that wouldn’t work somewhere on this planet.

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Rovers, hot-air balloons, landers, hovercraft, helicopters — you name it. Take a robot helicopter from Earth to Titan, and it could hover with only about a thirtieth of the power needed to hover on Earth, for example.

There’s lots on Titan to explore — as the solar system’s only just second largest moon (after Jupiter’s, Ganymede), it has a huge area of terrain with river channels, mountains, possibly ice volcanos, sand dunes, and, of course, the seas.

It is the three seas (Figures 1 and 2) — Kraken, Ligeia, and Punga Mare — and the many small lakes that have attracted the most attention from scientists since their discovery in 2007.

We know from just what few compounds are liquid at Titan’s cold temperatures that they must be made mostly of methane and ethane — the two main constituents of natural gas on Earth. What we don’t know is in what

Part 2 — Sailing Ligeia, Diving Kraken

By Ralph Lorenz

proportions, and what other stuff may be dissolved in them. After all, we already knew there was lots of other stuff made in Titan’s atmosphere. The orange-brown smog (Figure 1) that makes Titan’s surface hard to see optically is made of all kinds of organics produced by the action of ultraviolet light and space radiation on methane and nitrogen in the atmosphere. When this gunk was made in the laboratory on Earth by passing a Figure 1. Cassini camera color-composite spark into methane mixtures, Carl of Titan in 2014. This portrayal is slightly Sagan dubbed the tarry mix of false-color – the red channel in the picture here is actually of light in the near-infrared material ‘tholin’ after the Greek word for mud. This stuff — perhaps (940 nm – the same wavelength as the LED in a typical TV remote control) which pierces processed somehow in the lakes Figure 2. Titan's seas, as mapped by Cassini's the orange smog better than visible light. The radar instrument. Titan is tidally locked to Saturn, and seas to make the tiny haze North pole is towards the upper left, and the so Saturn defines the prime meridian and hovers in irregular dark spots there are Titan's seas. particles into bigger sand grains — the same part of Titan's sky, but shows phases like The fainter larger dark areas at the right of is probably what makes the sand our moon. Saturn is visible (dimly) from Kraken, but the image are the equatorial sand seas. The is below the horizon seen from the other two seas, dunes. Propane and other stuff planning of Cassini imaging of Titan is led by Punga and Ligeia.

Dr Elizabeth Turtle, my spouse. dissolved in the seas would make the liquid more viscous (perhaps 2017. So far, a few areas on Titan’s seas have shown like molasses or tar) and that might explain why Cassini transient evidence of roughness that may be the first observations hadn’t seen any waves in Titan’s seas. This has catspaw, or patches of wind-driven waves. If the climatebeen a surprise since in Titan’s low gravity and thick controlled theory is right, we’ll see more and more of these atmosphere, it should be easy to make waves. in the next couple of years.

Methane rainfall should be pretty clean; distilled pure All this, of course, is starting to look really interesting! like our own fresh rainfall. So, maybe at least some lakes or Rather than strain to interpret Cassini’s measurements from perhaps even a seasonal layer on top of the sea should be orbit to get a detailed composition, we need to measure ‘clean’ and not have a prohibitively large viscosity. There the composition of the sea directly — perhaps from a seemed to be a few features in Ontario Lacus’ shoreline capsule floating in it. Indeed, the Huygens probe was that suggested wave action might shape beaches, so waves designed to float, and had instruments to measure the sometime in the past must have occurred. By this time, amount of methane and ethane in the liquid — it just scientists were starting to improve computer models of landed in the ‘wrong’ place. Ideas formed in the late 2000s, Titan’s atmosphere (Global Circulation Models, GCMs — in almost as soon as the seas were discovered. effect, ‘weather models’) to the point where they seemed A joint NASA-ESA concept (TSSM — Titan Saturn to be useful — e.g., they predicted that Titan’s low latitudes System Mission) for a large ‘flagship’ mission that would should dry out. have an orbiter to visit the icy plumes of Enceladus as well The models said that the polar winds should be weak as Titan, and a hot-air balloon for Titan’s atmosphere also (well under 1 m/s) for most of the year, except during ‘floated’ the idea of a battery-powered capsule or lake summer. That, at least, was consistent with the lander to make a few hours of measurements in one of observations so far, but is only a theory that can be tested Titan’s seas. This big, multibillion dollar concept — while by observations in northern summer which we are only now scientifically attractive — was not followed up. starting to approach.

NASA had, however, started to develop a compact, Fortunately, the Cassini spacecraft has been operated efficient, nuclear power source for deep spacecraft called carefully and its fuel husbanded vigilantly, in order to allow the ASRG, or Advanced Stirling Radioisotope Generator. observations right until the northern summer solstice in SERVO 06.2015

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Post comments on this section and find any associated files and/or downloads at www.servomagazine.com/index.php/magazine/article/june2015_Lorenz.

Figure 4. Artist's impression of the Titan Mare Explorer (TiME) capsule.

From Ligeia Mare — even in summer — the Sun and Earth are low in the sky (Saturn is not visible from Ligeia).

Illustration courtesy of JHU Applied Physics Lab/Lockheed Martin.

Figure 3. In the special collection (a bit like the warehouse at the end of Indiana Jones) of the National Museum of Scotland, in Edinburgh in 2013 with Dr Elizabeth Turtle. On the right is one of the two demonstration engines built 200 years earlier by the Reverend Stirling himself. You can buy small engines that will run on the heat from a coffee cup.

Radioisotopes like Plutonium-238 generate heat as they decay, and this heat can be used to generate electricity in space — especially in the outer solar system — where we are too far from the Sun for solar cells to be effective. Until now, the technique used was to employ solid-state thermoelectric converters.

Having no moving parts, these are convenient and reliable — and Cassini’s long and productive mission has only been possible because of its three Radioisotope Thermoelectric Generators (RTGs) which put out over 850W at launch and a little under 700W now. (The thermoelectric generators slowly degrade, and the Plutonium itself has a half-life of about 87 years.)

The Curiosity rover uses a smaller RTG, developing about 100W of electrical power. The problem is that thermoelectrics are not very efficient — only about 5% of the heat gets turned into electrical power, and Plutonium is a very rare and expensive material. If the heat could be used to drive a small engine and alternator, the conversion efficiency would be much higher, and you could use much less Plutonium. The engine design (Figure 3) — using a single piston and a clever ‘regenerator’ to improve the efficiency — was actually invented by a Scotsman, the Reverend Robert Stirling in 1816 (since I am a Scot myself, I feel obliged to mention the location).

NASA solicited ideas in 2007 for missions that might particularly benefit from a small radioisotope power source: the ASRG. Cassini radar scientists, Ellen Stofan and Jonathan Lunine, with myself and the aerospace company Lockheed Martin, thought that a long-lived Titan sea capsule would be a great application for the ASRG, and NASA funded us to do a short study which we called the Titan Mare Explorer (TiME; Figure 4).

This study developed quickly into a more detailed mission proposal, submitted in 2010 to NASA’s Discovery

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competition. Here, 28 different ideas for missions costing $425 million or less were evaluated in a cut-throat process, with only three being picked for a further ‘Phase A’ study.

These three — announced in April 2011 — were GEMS (a Mars Geophysical Mission), Chopper (Comet Hopper), and TiME. Both Chopper and TiME proposed to use the ASRG, which it seemed NASA really wanted to fly.

Winning a $3M study contract is, of course, good news — a vital step in bringing a mission to flight. It also means a lot of work in figuring out the details. Suddenly,the height of the waves on Titan’s seas was no longer of merely academic interest — we would have to work out what the dynamics of the capsule would be so that camera images wouldn’t be blurred by the pitching deck, and in order to make the mission at all affordable, we relied on sending data directly back to Earth with a steerable antenna without using an expensive orbiter relay spacecraft.

Now, pointing antennas from moving platforms is done by drones, cruise ships, and airliners all the time (people like their satellite TV!), so it is a straightforward engineering problem but needs a specification so that the motor and gearing on the antenna mount can be designed. How big will the waves be, for how often?

So, now I’m an oceanographer. We developed a physics-based model of wave growth and propagation on Titan (in the low gravity, waves actually propagate in slow motion compared with Earth), so for a given windspeed, we’d know how big the waves are on average (about 20 cm high for a 1 m/s wind, as it turns out). That, of course, demands the next question: How strong are the winds going to be — specifically on Ligeia Mare (at the time in 2011, the best-mapped of Titan’s seas, and so our safest splashdown target) on 3rd July 2023, which is when we’d arrive if we were selected for a launch in early 2016.

Weather prediction with GCMs is far from perfect — even on Earth where the models can be tuned with millions of datapoints from weather stations, satellites, and balloons. Beyond a few days, different models diverge on their predictions of the tracks of individual storms. So, what

Figure 5.

Splashdown tests with a 1/7 scale model of TiME. I instrumented this model (which was made with a 3D printer) with accelerometers, gyros, and dataloggers from sparkfun.com, as well as an accelerometer logger from www.gcdataconce pts.com.

hope do we have of predicting weather on Titan? We have to resort to statistical analysis. If we assume the worst reasonable value and apply some safety margin in our design, we have an acceptable chance of success. In the space business, that usually means 99%. After all, even our most reliable rockets fail one or two percent of the time.

So, what’s the worst reasonable value? We looked at data from no less than four different GCMs, and while they differed on their predictions of exactly when in the Titan year the winds pick up and in what direction the winds blow, the models were all pretty consistent in their maximum wind speeds in 2023 — winds were less than about 0.8 m/s for 99% of the time.

This is well after mid-summer, when winds might be somewhat stronger. For comparison, the wind measured by tracking the Huygens probe in the last moments of its descent were about 0.3 m/s.

This sort of environment specification is one of the most interesting jobs I’ve done in my scientific career. There is a certain circular perversion to it, in that we have to figure out estimates of parameters in order to design instruments and the machines to carry them, in order to actually measure those parameters! We had to estimate the winds at high altitude too, as these would affect how far the capsule would drift during its parachute descent. How big to make the parachute? The smaller you make it, the harder the capsule hits the sea and the tougher the g-loads at splashdown. Make it too large, and the capsule descends slowly and has longer in the air to drift, so it increases the chance you miss the sea altogether.

We didn’t actually look in the phonebook, but it seemed a fair bet that there aren’t many people around who work on splashdown mechanics, let alone splashdown into liquid hydrocarbons. Since I had looked into this problem as a student for Huygens, I regressed slightly to dabble in some engineering tests in this area. We would use computer models to estimate the full-scale loads in Titan liquids and Titan gravity, etc., but wanted to fine-tune those models with scale model splashdown tests on Earth.

We sought the help of colleagues at Penn State, who set up a drop test rig over a water pool at their Applied

Figure 6. The team at APL used computer models to study the motion of the TiME capsule in Titan's seas, and even its interaction with the seabed in case the capsule washed up on a Titan beach.

Research Lab, and did a couple of hundred test drops (Figure 5), giving us the data we needed to be sure of a safe splashdown that wouldn’t over-stress the ASRG. The ASRG was essential to TiME for a couple of reasons. Not only did it supply electrical power, but the ‘waste’ heat would keep it warm in the ultra-cold Titan environment. Spacecraft in orbit can be kept warm — even far from the sun — with relatively little power by using special coatings that reduce the radiation of heat, which is the only way surfaces can lose heat in a vacuum. In Titan’s thick cold atmosphere, convection wicks away the heat promptly, and so we would need the heat from the ASRG to maintain acceptable temperatures.

These are just a few of the areas we dealt with in our Phase A study, which was over in a blistering 10 months or so. One fun aspect for me as a space guy was working with people from the other areas in my own employer, the Johns Hopkins University Applied Physics Lab (APL) in Laurel, MD, which was originally set up to do work for the US Navy. The dynamics of the capsule in the waves (Figure 6) were modeled by an engineer from APL who usually worked on Navy projects. Similarly, to measure the depth of Titan’s seas, we would use an acoustic depth sounder (much like a fish finder, or a high-power version of the ultrasonic rangers used in amateur robotics), and APL had sonar experts we could call on. A fun set of tests we did demonstrated that our preferred sonar transducer design (Figure 7) actually worked better in liquid nitrogen than it did at room temperature in water!

After preparing a ~1,000 page report detailing schedules, costs, vendors, assembly procedures, orbital trajectories, heat shield loads, scientific observing plans, data archiving procedures, and everything else, we waited.

However, NASA’s development of the ASRG met with some hiccups that summer, and in August 2012 — a couple of weeks after the RTG-powered Curiosity rover landed on Mars — NASA announced that it had selected the InSight SERVO 06.2015

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Figure 7. A beefy sonar transducer, covered in frost at left as it is still cold from a test in liquid nitrogen. The conical section covered in frost helps couple the acoustic energy into the liquid, while a heavy steel back-end helps reflect the energy from the piezoelectric ceramic (gray band in middle) forwards. This sensor configuration goes by the German name 'Tonpilz' ("sound mushroom") and actually used the same piezoelectric ceramic as the Huygens penetrometer (see previous article).

mission to Mars (GEMS had been renamed InSight, as it turned out a previous mission had been called GEMS) to fly.

We were devastated.

We had hopes that we might get the chance to propose the mission again, but NASA suspended the ASRG program in 2013. Perhaps the mission could be done with an RTG — there would be more waste heat than would be ideal, but that could be managed with bigger heat pipes.

When NASA announced a solicitation for new Discovery concepts in February 2014, it revealed that the pace of certain steps in the Plutonium fuel production process (the material has to be sealed in special iridium alloy capsules for safety in the event of a launch accident) meant there would not be enough to allow an RTG to be ready for a Discovery mission this time around (with missions selected for Phase A in 2015, a launch might happen in 2020, and one might arrive at Titan in 2026/2027).

So, that was that. We were dead in the water, so to speak. Even if in another couple of years NASA was ready with a radioisotope power source — whether ASRG or RTG — launching in the early-mid 2020s wouldn’t allow arrival until almost 2030, when it would be well after the Titan northern fall equinox (Figure 8). The Sun and the Earth would then be well south of the equator, and thus below the horizon as seen from Titan’s arctic seas. The efficient direct-to-Earth communication plan would be impossible.

One could imagine a capsule in the dark, communicating via a relay spacecraft, but that won’t fit in the Discovery program’s cost box. So, exploring Titan’s seas has become more of an exercise in imagination for now.

Freed of the constraints of near-term implementation

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Figure 8. Twilight on Kraken. As Titan's long seasons march on, the Sun and Earth get too low over Titan's northern seas to offer useful line-ofsight for communication after about 2027; missions without relay satellites will have to wait until around 2040 for the geometry to improve again.

details, it is easy to consider not just free-floating capsules but boats, hovercrafts, or submarines. It is just such farreaching ideas that NASA’s Institute for Advanced Concepts (NIAC) likes to explore, and last year they funded a team led by Steve Oleson at Glenn Research Center in Cleveland, OH to pursue how a submarine might look. The team included myself to define the scientific goals and environment, and experts from Penn State ARL to consider the hydrodynamics of propulsion and buoyancy control.

What could a submarine do? For a start, we could go wherever we wanted to go scientifically. For example, after landing safely in the middle of Kraken, we could sail northeast to inspect the eastern shoreline and profile the depth, then turn northwards to ‘sniff’ whether liquid emerging through a labyrinth of channels from Ligeia Mare might be more methane-rich than the main body of Kraken (much like the Black Sea draining into the much more salty Mediterranean).

Then, we could cruise around the western margin of Kraken, where the wind patterns may lead to different amounts of wave action and thus different shoreline morphology (beaches, cliffs, etc.). A big motivation for inspecting shorelines and the seabed is that there is evidence (seen in Cassini data) of evaporites: bright oncedissolved material precipitated onto what is now land when more extensive seas dried up to their present extent. Such evaporites formed a ‘bathtub ring’ on Lake Mead and Lake Powell due to a recent drop in water level. Yet, like those two bodies — which have an irregular shape, filling canyons and valleys that were once in the open air — the shape of some of Titan’s shorelines suggest the sea level has been rising. So, there is an interesting climate and sea-level history that we are only just starting to see hints of in Cassini data that a submarine could explore in detail.

We thought about different shapes, like boxy Underwater Autonomous Vehicles (UAVs) with gripping arms and lots of side-thrusters for maneuvring as used in the oil industry or for mineclearing (ideal for scientific sampling of the seabed), or a saucer-shaped submersible like Jacques Cousteau’s ‘SP-350 Denise,’ as well as more conventional torpedo shapes.

An important consideration is that we would need a big antenna to beam lots of data back to Earth. Since we could choose where we went and could carry a sidescan sonar to image the seabed and a camera to image the shoreline, we’d want to send much more data back than TiME would.

In the end, the best shape appeared to be mostly torpedo-like, with a large dorsal ‘sail’ carrying a phased-array electronically-steered antenna (Figure 9) that would be able to lock onto the Earth and Figure 9. Titan submarine configuration, with the various scientific and transmit, without having to worry about mechanically navigation sensors shown. Note the long ballast tank, the thrusters at the rear, and the large flat dorsal phased-array antenna. compensating for rolling in the waves.

A driving requirement turned out to be the allows the back cone to swing open easily to insert the desired speed of sailing. We wanted to sail around one side ASRGs at the launch site. of Kraken in 90 days — a trip of 1,800 km. This would A couple of interesting challenges relating to the Titan mean an average speed of about 0.3 m/s — and faster environment emerged. First, buoyancy. At least some undersea dashes if we sailed only slowly while surfaced and submarines on Earth may need to deal with the difference communicating with Earth. This strategy made sense with in density between seawater and freshwater (about 3%). To our planned 1 kW of ASRG power (we assumed these have a save performance margin in both environments and systems will be ready in 2040, when it is the next summer allowing for consumables on board, a terrestrial sub in Titan’s north). We would alternate between swimming at typically has buoyancy tanks that can accommodate about about 1 m/s for most of each day with almost all the 10% of the vehicle weight. The difference between liquid power devoted to propulsion, and cruising on the surface at methane and liquid ethane (the relative amounts of which about 0.4 m/s (enough that the sub can maintain headway may differ between Kraken and Ligeia, or even within and keep a steady heading) while using most of the power Kraken), however, means we would need some 30% of for the data transmission. buoyancy tank space if we want to deal with both Steering would be by differential throttling of four environments. For the moment, we assumed that as Cassini thrusters at the back. Having such an arrangement also data continues to come in, we should have an idea of what to design for in 2040.

A second issue relates to the thermodynamics. On Author Earth, we can use compressed air to ‘blow the tanks,’ to www.lpl.arizona.edu/~rlorenz push ocean liquid out of the buoyancy tanks to surface. On Titan, the nitrogen atmosphere is much closer to its Author talk on sailing the seas of Titan condensation point (94K is not much more than the boiling www.youtube.com/watch?v=l7nANi6WK2k point of nitrogen; about 80K at 1 bar). Once we get to depths of a few hundred meters, the pressure is such that NASA Cassini website, with latest pictures of Titan the nitrogen will condense! So, we needed to use a positive http://saturn.jpl.nasa.gov displacement system, a piston or diaphragm, and a gas that NASA Institute for Advanced Concepts (NIAC) wouldn’t condense (helium or neon) to push the sea liquid www.nasa.gov/directorates/spacetech/niac/ out of the tanks.

A third related challenge involves cavitation. When fastVideo of the Titan Submarine in action moving surfaces underwater develop a lot of suction (as, www.youtube.com/watch?v=NnKxbdpLP5E for example, a propeller must in order to develop thrust), the local pressure can drop to the point where air dissolved Related N&V/SERVO Articles in the water comes out of solution and forms bubbles.

R. D. Lorenz, “Java Power – Building a Thermoelectric Mug,” Nuts & Volts, September 2004, pp.46-49 (shows how thermoelectric power The impact of these bubbles can erode propellers and generation can work – albeit less efficiently than a Stirling engine) is also a major source of noise which is, of course,

Resources

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Figure 10. A slender submarine would fit neatly in the USAF/DARPA X-37B winged entry vehicle. (Human for scale.)

particularly undesireable for military submarines wishing to remain undetected.

The same problem confronts us on TItan, where the ocean is closer to its vapor equilibrium than is water on Earth. It is exacerbated by the kilowatts of waste heat seeping out of our hull (we have insulation on the inside of the hull to force that heat leak to keep the interior warm, but it ultimately is rejected to the environment). The temperature rise isn’t enough to boil methane or ethane, but it is enough to cause dissolved nitrogen to bubble out.

So, there may be a gentle fizzing around the vehicle, like on a glass of soda. This wouldn’t be enough to ruin the hydrodynamics of propulsion, but it may degrade the performance of the imaging sonar.

Our two-week study was never intended to solve all these problems — only to identify them and point out some major design trades and options to explore in the future.

Something we may look at in future studies is whether changing the antenna design — if there were an orbiting

Figure 11. Cassini radar map of Titan's largest sea, Kraken Mare, showing named islands, straits, and inlets. The IAU convention is for islands to be named after mythical islands, inlets after real bays and fjords on Earth, and straits to be named after characters in Asimov's Foundation series of sci-fi novels.

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relay spacecraft — might change the overall operations approach or vehicle shape.

It turns out that liquid methane and ethane are rather transparent to radio waves (in fact, Cassini’s radar was able to probe the seabed of Ligeia Mare through some 160 m of liquid in 2013), so perhaps a submarine could send data back to an orbiter without ever having to

surface.

Another fun trade is the delivery system. A torpedo shape does not fit very well into the traditional blunt-cone entry shell (this shape gives a strong shock wave during the hypersonic atmospheric entry from space, and so reduces the heat loads). This isn’t the only possible shape, fortunately. There are inflatable entry shields under development by NASA’s Langley Research Center in Hampton, VA, and an umbrella-type deployable heat shield being explored by Ames.

We rather liked another possibility — and NIAC is just the place to think outside the box like this — that the slender hull would fit rather nicely (Figure 10) in the cargo bay of a scaled-down Space Shuttle, which enters Earth’s atmosphere at about the same speed (7 km/s) we’d enter Titan’s. The US Air Force has flown a scaled-down unmanned Space Shuttle: the X-37B. Such a winged entry vehicle allows a lot more flexibility in arrival conditions, and can fly a long distance within the atmosphere to hit a desired landing point.

One possibility would be to extract the submarine from the shuttle using a parachute (like the Mother of all Bombs — MOAB). A way even more elegant choice (can you tell we had fun doing this study?) would be to just land the whole thing at sea. In fact, ditching tests were done on a scale model Space Shuttle in the 1970s. If you keep the nose up, it glides nicely to a stop. Then, with doors opened, the shuttle would be allowed to sink and the sub would swim away.

The concept gets easier to explore all the time — more and more Cassini data are coming in, improving our understanding of Titan’s winds and seas. A few weeks ago, the IAU approved a set of names for straits and inlets on Titan, so our mission plan for cruising around Kraken no longer has to say ‘the big estuary at the northeast end of Kraken,’ but can now say ‘Moray Sinus.’

Predicting the future in space is hard. There are lots of exciting possibilities for Titan missions — not just orbiters, balloons, and capsules, but landers, rovers, airplanes, and so on. Maybe a submarine won’t be the next step, but starting to think about the details of how one might go about doing such an amazing mission just whets our appetite about this wonderful world, and makes us look anew at how we do things — even submarines — on Earth.

SV

Animatronics for the Do-It-Yourselfer

By Steve Koci

Quality animatronics have long been the domain of well staffed, professional prop shops. However, with the considerable progress and improvements, and the many new products currently available, it is now possible for the home hobbyist to create and control incredible creations.

W

hat is my definition of animatronics? To use a mechanical creation to provide a lifelike appearance to an otherwise static prop. This could be as simple as animating an arm to reach out at a guest, to the creation of a fully articulated and talking character.

In upcoming months, we will explore new ideas and methods for building your own quality props.

This will be a journey of discovery and experimentation as we explore the wide variety of motors, materials, and controllers available today. Hopefully, we will also invent some new methods which will allow our creations to become even more lifelike.

Although my focus and primary reason for getting into this hobby was to create characters that would be integrated into my Halloween display, there are many other opportunities to utilize animatronics. In addition to amusement parks and holiday displays, some other examples of how animatronics can be used is for school The success of this adventure into animatronics will rely on the participation of our entire collection of readers and builders. In order for this community to flourish, we all need to be willing to share and brainstorm our ideas.

I welcome your contributions, your ideas, and resources. Your design may spark an idea or be the one puzzle piece someone is missing to bring their creation to life.

Please submit ideas of things you'd like to see.

Although the build list for the next several months is already laid out, I'm always looking for new ideas for future articles.

projects, in film and stage productions, model railroads, teaching aids, and as store displays to interact and entertain customers, just to name a few.

How Did I Get Here?

My interest in building my own animatronics began when I discovered the online Halloween display community.

I was looking to expand on what I had been doing, and wanted to take the leap from a static display to one that incorporated movement.

Living in Southern California allowed me the opportunity to visit Disneyland and experience all it had to offer. I’ve always been intrigued by the characters in the park, and often wondered what it would take to actually build them. Although I don’t have an engineering or electronics background, I found plenty of knowledgeable people on various Internet chat groups and forums that were willing to share their experience and assist me as I learned the skills necessary to complete the characters I was dreaming up. I always enjoy a new challenge and was ready to learn, so I made progress quickly.

My Halloween display quickly evolved into a wonderful moving, talking, Disney-inspired production. Each year, the challenge is to continue to take it to new levels. I’m always on the lookout for new techniques that will allow my display to improve.

In this article series, I would like to explore the many methods, materials, and techniques available to the hobbyist that will allow us to construct and control our own animatronics. A major challenge will be to discover ways to SERVO 06.2015

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DIY Animatronics Post comments on this section and find any associated files and/or downloads at www.servomagazine.com/index.php/magazine/article/june2015_Koci. character is planning for the exterior dressing that will bring my mechanisms to life. The parrot was no different. We explored all sorts of options including toy parrots, yard decorations, and even feathering our own. After a year of searching, we finally came across the solution on a trip to the MGM hotel in Las Vegas, NV. While browsing in their store on the casino floor, we found the perfect item. A puppet — complete with a large area normally used to put your hand. This would now become the perfect vessel for the mechanical skeleton. With that problem solved, it was now time to design the inner workings, keeping in mind that whatever we designed had to fit inside the cavity of the puppet.

Everyone has a different philosophy when it comes to laying out the initial design of a mechanism. For me, I like to do a simple drawing to keep me from forgetting something and then construct a basic prototype. Rarely does the final project end up looking like the original design. It seems — more often than not — that the designs that work in my head don’t work quite as well once assembled. Adjustments and refinements are always necessary!

Bandit Begins to Take Shape Figure 1. Bandit, the swashbuckling parrot.

do this while on a DIY budget. However, knowing the ingenuity of this community, we will come up with solutions that enable us to produce characters that will rival those put together by the professional production shops.

So, without any further delay, let’s get into our first project.

Meet Bandit, the Swashbuckling Parrot I’d like to introduce you to Bandit, my Pirate Parrot. He was inspired by the birds in the Tiki House at Disneyland. Of course, any pirate worth his salt is going to have a parrot close by. Bandit will be an appropriate place to start our project of discovery as it’s a character I built from the ground up. He was constructed without the use of any premade components or mechanisms. The necessary materials could all be purchased from the local home repair store, and basic hand tools were all that were required to build the basic mechanism.

The servos and linkages came from ServoCity which carries a wide variety of servos, motors, controllers, and linkages. We will explore some of the many products they stock that will make our jobs easier in future builds, but for this project, I wanted to show what’s possible to do on your own.

One of the major obstacles I face when building a

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Before I even started the build, I needed to determine the specific movements that I wanted the parrot to do. In addition to speaking, I wanted the body to move in multiple ways: I wanted his jaw to move in sync with the audio track; have him be able to nod his head; bend at the waist; and have his wings move. For the range of motion, I prefer more subtle movements for my animatronics versus having their movements be wild and exaggerated. Just because a mechanism is able to have a wide range of motion doesn’t mean you have to use it. With these facts in hand, I could begin gathering the required materials and start laying things out.

For this project, I chose to utilize four HiTec 425BB servos which (along with the linkage parts) came from ServoCity. One servo was to move the jaw in sync with the audio track; one was needed to move the wings; and the other two to rock the body and neck forward and backwards. This model is my servo of choice as it has sufficient torque for most of my needs, it’s reliable, and the price is very reasonable. I don’t have any qualms about using a more powerful unit if it’s required, but I also don’t like to spend the money on more servo than an application requires (Figure 2).

For the framework, I decided to go with aluminum stock that can be picked up from your local “big box” hardware store. It is convenient to be able to just run down the street to pick up material whenever I need it, but the cost can be high. I’m fortunate enough to have a large metal supply house which is where I pick up the majority of

DIY Animatronics my steel and aluminum stock that I use to build my frameworks. I chose aluminum for this build as it had enough strength to get the job done while keeping the weight to a minimum. Aluminum is easy to work with using common hand tools.

A hack saw, a drill with appropriate bits, and a file are really all you need to get started building articulated mechanisms with aluminum.

We Have the Tools to Build Him In order to have a place to mount the servos, I first had to cut and assemble the aluminum structure.

All three of the body servos would be attached to a single piece of 2 x 1-1/2 inch L shaped channel. This allowed me enough room to place the servos on both sides so they would not interfere with each other. The waist and Figure 2. The completed skeleton ready Figure 3. Neck and waist servo mounting. neck servos were placed on the two inch side, and the wing servo to be dressed. on the 1-1/2 inch side. individual pivot points and added a center ring to run the I first traced out the dimensions of the servos. Then, lines. I then connected them to the servo horn using using my Dremel tool with a cutting disc, I did most of the braided fishing line. This was an work and finished the cuts with a easy and inexpensive solution, and small hacksaw. The rest of the allowed me to easily adjust the skeleton was constructed of 1/2” range of movement of each wing aluminum stock. I used the heavier (Figure 4).

1/8” thick for the main body and The plan for the jaw servo was 1/16” for the wings. for it to be mounted in the chin The body movement which and would again be connected allowed the parrot to move at the using the braided fishing line. waist would be accomplished by Getting this part of the mechanism adding a servo in the main body to work properly ended up being area and attaching a linkage to the most time-consuming. I one of the legs. The parrot also originally designed it using fishing needs to be able to nod his head. line like I had done with the wings.

This was a fairly easy placement to This would open the mouth and figure out and install (Figure 3). rely on gravity to close it. This The connection — like all those method worked fine with the wings requiring a rigid link — was made where I had the added weight and using threaded 4/40” rod and ball leverage to allow this to function joints. properly. However, the beak lacked Since the wings would move sufficient weight to allow it to close together, I could get the quickly enough. My revised method movement I wanted using a single Figure 4. Wing servo and pivots rigged was to use a rigid linkage that servo. I installed the two wings on with fishing line.

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DIY Animatronics RESOURCES ServoCity www.servocity.com Tenda Stereo Audio Board www.mdfly.com/products/sd-card-mp3-player-modulers232-ttl.html Parallax Passive Infrared Sensor www.parallax.com/product/555-28027 Scary Terry's Website www.scary-terry.com/audioservo/audioservo.htm PICAXE Program Editor www.picaxe.com/Software/PICAXE/PICAXE-Editor-6 My Website www.halstaff.com YouTube Video https://youtu.be/OqnFj31UC80 Figure 5. Final jaw servo mechanism.

Figure 6. A view of the underside attachment points.

would drive the jaw open and then close it.

I would have preferred that the servo had driven the jaw linkage from the bottom instead of the top as it would have given me a better angle. However, the design of the puppet would not allow it to move freely that way. Just another one of the compromises you must often make in constructing something like this (Figure 5).

The puppet did require a bit of careful surgery to allow the aluminum pieces to slide into the wings, as well as cutting slots for the leg pieces to go through the bottom of the feet. This made for a very clean installation with no signs of the aluminum skeleton visible. Once this was done, the legs were attached to the wooden base using two 3/4â&#x20AC;? corner brackets (Figure 6).

Bandit still needed a little something to finish him off.

The addition of a mask really gave him a swagger and

Figure 7. Bandit on his perch and all his hidden electronics.

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DIY Animatronics Figure 8. Controller boards secured in their home.

some extra character!

All the final attachments were made with bolts, washers, and lock nuts. I prefer to use the ones with the nylon inserts for a secure connection. While making the modifications, however, I usually use regular nuts to speed up assembling and disassembling. This makes things much easier, plus I donâ&#x20AC;&#x2122;t have to use a wrench to do it.

Bandit would entertain our guests from his own wood perch mounted to the side of our pirate facade (Figure 6). His base was constructed with ample room to hide his controllers and the necessary speakers from view (Figure 7).

Projects like this always require an extensive amount of tweaking. Finding the perfect placement for the servos and proper lengths of the linkages takes some patience. You need to be willing to adapt your original design in order to

LISTING 1 #Picaxe 18M2 'C.1 'B.1 'B.2 'B.3

is is is is

Symbol Symbol Symbol Symbol

to Tenda Waist Bend Spread Wings Head Nod Waist = B.1 Wings = B.2 Head = B.3 Tenda = C.1

Init: serout Tenda,4800, ($EF); 'STOP MP3 module pause 1000 serout Tenda,4800, ($E1); 'Set MP3 volume pause 1000 Servo Waist, 50 Servo Head, 210 Servo Wings, 170

achieve the best result possible. Sometimes it is a matter of space, or it could be that a linkage is binding, or maybe youâ&#x20AC;&#x2122;re just not getting the exact movement youâ&#x20AC;&#x2122;re after.

Whatever the reason, make sure to set plenty of time aside

servopos Waist, 150 pause 1000 servopos Waist, 100 pause 3000

servopos wings, 90 pause 250 servopos wings, 170 pause 5000

serout Tenda,4800,($01) 'Start playing first mp3 pause 500

servopos Waist, 150 pause 1000 servopos Waist, 90 pause 2000

servopos Waist, 50 pause 1000 servopos Waist, 100 pause 3000 servopos Wings, 90 pause 250 servopos Wings, 170 pause 1500 servopos Waist, 150 pause 1000 servopos Waist, 75 pause 1500 servopos Head, 100 pause 1000 servopos head, 160 pause 1000 servopos wings, 90 pause 500 servopos wings, 170 pause 1500

Routine: servopos Head, 130 pause 1000 servopos head, 210 pause 1000 servopos Wings, 90 pause 250 servopos Wings, 170 pause 1500

servopos Waist, 120 pause 1000 servopos Waist, 90 pause 2750 servopos Head, 210 pause 1000 servopos head, 140 pause 1000

servopos Head, 210 pause 1000 servopos head, 140 pause 1000 servopos wings, 100 pause 500 servopos wings, 170 pause 2500 servopos Head, 130 pause 1000 servopos head, 180 pause 1000 servopos Wings, 90 pause 250 servopos Wings, 170 pause 1500 servopos Waist, 150 pause 1000 servopos Waist, 100 pause 3000 for time = 1 to 60 '60 is the number of 'seconds of retrigger 'delay pause 1000 'Pause for 1 sec 'next time goto Routine

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DIY Animatronics

Figure 9. Audacity screenshot showing the split audio track.

to make the necessary modifications. Some extra time spent on this step can make all the difference in the performance of your completed prop.

Bandit Needs a Brain!

I decided to use two of my custom boards to control the prop (Figure 8). The first was my Kitchen Sink controller which provided me with the stereo audio player, and was able to control the three servos for the body movements. It uses a PICAXE 14M2 processor with an

onboard Tenda stereo audio card (see Resources). This audio card utilizes an SD card to store the tracks and allows me to control the track being played, as well as letting me control the volume. Using this controller also allowed me to program it so that it either could be triggered by a passive infrared sensor (see Resources) or run on a loop.

To control the jaw and allow it to be synced to the audio, I used my version of the Scary Terry board. This board was originally designed by Scary Terry whose website you can find listed with the other resources. There have been several people who have revised the original design and this is my version.

An enclosure for the controllers was required, so I went to my favorite. When I first started putting together my own boards, I searched for a reasonably priced container to house them. I often found that I was spending more on the enclosure than I was on the completed controller. What I needed was something that was lightweight, easy to modify, watertight, and inexpensive. The best solution I found was in my own kitchen. The new plastic food containers used to store our leftovers were ideal for my needs. My wife soon tired of searching for missing containers and now routinely restocks my supply. It doesn’t even come out of my build budget anymore. Perfect!

The audio is first prepared using the free software download called Audacity. The original stereo track is split into a right and left channel, and the right channel’s audio is replaced with a tone track which drives the jaw circuit (Figure 9).

If I was to build this now, I’d replace these two boards with one of my Frankenstein boards. This board allows me to combine all the functions necessary to control the parrot in a single board, thus making a cleaner installation as well as saving space. A link to my website showing the boards I’ve made to run my haunt is included with the Resources.

Another modification I plan to do is to replace the existing jaw servo with one with a little more torque to improve the action.

The code I used was very basic. It took a little bit of adjusting to get it just right, but before long Bandit was moving. One of the reasons I like working with the PICAXE (besides its easy-to-learn programming language) is that the program editor is free (see Resources) Be sure to check out the code back in Listing 1.

With that, Bandit was ready to be put on display. You can check him out performing on his perch at https://youtu.be/OqnFj31UC80. SV

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By Dave Prochnow

littleBits and the ActoBitty Post comments on this article at www.servomagazine.com/index.php/magazine/article/june2015_Prochnow.

SERVO Magazine readers are well aware of the magnetic circuit building power of littleBits (see articles in the November 2014, December 2014, and February 2015 issues). Similarly, readers are also knowledgeable of the structural capabilities of the Actobotics modular aluminum building system, as there have been countless articles on these parts, as well. (In fact, Actobotics is mentioned in several places in this issue.) Curiously, using magnets with aluminum doesn’t appear to be a very attractive combination.

emarkably, both of these seemingly divergent systems do play nice together. The result of this union is ActoBits, described here.

First of all, let’s be up front and clear here: The littleBits magnets are not used for fastening the modular control system to the aluminum channel. The magnets are used for attaching each of the littleBits modules together into a simple light sensor based robot control system.

These sensors, in turn, control the two ActoBitty motors which cause our robot to either steer towards light, or avoid light and seek darkness instead.

Choosing the robot’s light reaction behavior is easy with this simple

R

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Figure 1. The power supply nests inside the ActoBitty channel, while the littleBits control hardware neatly seats on top of the channel.

The black post jutting out from the bottom of the ActoBitty is one of the kit's battery mounts.

magnet based construction technique: Flick a switch on a light sensor module and you have a light-seeking robot.

Flick the same switch and convert your photovore (light eater or light seeker) into a photophobe (fearing light or darkness seeker) robot.

All of the required modules — including the two light sensor Bits — snap together and rest comfortably on top of the ActoBitty channel. A completely “wired up” ActoBits is shown in Figure 1. The total assembly time for building your own will be roughly one hour.

The Build You will need seven Bits along with the Actobotics ActoBitty kit for building ActoBits: littleBits Modules • Power p1 [plus the requisite 9V battery]

Figure 2. Use two proto modules (w9) for connecting the ActoBitty motors to the littleBits control hardware.

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• Fork w7 • (2) Light sensor i13 • (2) Proto w9 • (Optional) Light wire o16 Actobotics • The ActoBitty kit #637146 NOTE: Except for the unusual proto Bit (w9), each of the littleBits modules can be individually found in the littleBits online store, or they are included inside various popular littleBits kits or module collections (e.g., Space Kit, Deluxe Kit, etc.). The proto Bit is a little harder to find. Luckily, two proto modules are included inside the littleBits Hardware Development Kit (HDK 680-0005). Begin your assembly of ActoBits by building the ActoBitty kit. This is a straightforward intuitive build with only two minor deviations from the online assembly instructions.

First of all, route the motor wires through the large holes on the channel’s side before you mount the motors. Running the wires through these two rear holes will streamline your final robot design and ease the connection of the motors to the littleBits control system, as well as help keep the wires away from the spinning wheels.

The second modification to the ActoBitty kit build isn’t near as dramatic as the first — the simple removal of the AA battery holder. Power for this entire project will be supplied via the 9V littleBits power module instead.

Whoa there! Every sharp-eyed robot reader must be wondering how this 9V power supply is able to both drive the two ActoBitty motors and operate the light sensor control system. Technically, you’re correct. This design should support two commercial motor drivers or — at the very least — two minimal H-bridge motor drivers for isolating the control system. Yes, these drivers could be added to the littleBits circuit, but the robot can still operate without them. Performance does suffer in this driverless configuration, but neither the motors nor the control circuitry will be damaged.

Advanced users might opt to build a couple of Hbridge motor drivers on a littleBits perf module (w29), then substitute this module for the proto modules. A perf module is included along with the proto modules inside the littleBits HDK. Throwing caution to the wind, the ActoBitty motors are plugged into the littleBits proto modules — one motor per module. Each connection is made by removing the jumper blocks from the three sets of pin headers located between the screw terminals, and plugging the motor’s red and black wires into the SIG signal pin and the GND ground pin. Figure 2 shows this attachment.

Connecting both motors in this fashion converts ActoBits into a spinning “head bot.” In other words, the robot simply turns on its wheels, pointing its sensors towards light or darkness depending on how the light sensor module switch is set (i.e., light or dark). If you want ActoBits to drive towards light or darkness, then you must reverse the polarity of one motor. The simplest way to do

also minimizes visible wiring which can get snagged on furniture as ActoBits runs around on the floor.

One optional bit that can be added to the completed ActoBits build is the light wire module (o16). This module is included in the littleBits Figure 3. A layout diagram Deluxe Kit. Consisting of for the littleBits control hardware. almost four feet of electroluminescent (EL) wiring and inverter circuitry, the light wire module produces a soft blue glow along its entire length. Even better, you can wrap it, bend it, and even tie knots in it without destroying its soft EL glow.

Therefore, you can use the light wire module to this is to switch one motor’s black wire to the SIG pin, and strap down the littleBits control system to the aluminum the red wire to the GND pin on one proto module. channel, as well as add a “cool” glow to the completed Based on this motor polarity knowledge, there are four project as shown in Figure 4. Just make sure the EL wiring modes of operation that you can test with ActoBits: doesn’t interfere with the light sensor module’s controls. clockwise head bot spin; counterclockwise head bot spin; Want more? Like increased processing power, pull forward drive; and push forward drive. Remember, connectivity, or multimedia? each operational mode is set by altering the way the Lacking a microprocessor isn’t a big deterrent to ActoBitty motors are plugged into the proto modules.

ActoBits. If you need greater “brain power,” the littleBits Now that the motors are wired up, it’s time to turn on universe can provide you with a magnetically-connected the power switch and see what happens. Depending on Arduino module (w6) or an Internet-connected magnetic your selected motor mode of operation, the ActoBits robot cloud bit module (w20), or even an MP3 player module will start moving or spinning. You can add some control to (i25) — everything you need for getting smarter, online, this movement by adjusting the light sensor module (i13). and singing your own praise.

There are two controls on the light sensor: light mode So, who said magnets can’t be used with aluminum? and sensitivity. The light mode has two settings: light and SV dark. Using the light setting makes the sensor increase its signal output as light intensity increases. The dark setting is a little harder to understand. The sensor signal increases as light intensity decreases.

You can further fine-tune this signal response by adjusting the light sensor sensitivity. Alter the sensor light mode settings to dramatically change ActoBits’ behavior.

Likewise, use the sensitivity control for fine-tuning the robot’s movement during its quest for light.

Final Bits to Trick Out ActoBits Follow the diagram in Figure 3 for laying out the littleBits modules for easy placement in the ActoBits robot.

The 9V battery is stowed inside the aluminum channel.

There are two Actobotics battery mounts included with the kit that will hold the battery in place.

When the battery is in place, route the 9V battery power plug through the frontmost hole on the top side of the channel. This installation will not only help hold the entire littleBits control system in place on the channel, but it

Figure 4. Adding the optional light wire module (o16) to the robot produces a great ground effect lighting system.

Plus, the light wire is robust enough to act as a skid when driving around.

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CNC Part Creation Workflow Milling Vise Setup Figure 1.

n this first article, I’ll cover attaching and tuning a milling vise to your CNC machine. You might ask, why do I need a vise? Why not just clamp the work piece to the table? The answer is there are advantages to using a vise:

I

• Once the vise is tuned and the fixed jaw referenced to your machine, it is very easy to attach stock to your machine without realigning each piece that is clamped directly to the table.

• There are times you need the part raised off the table so it can be milled properly.

• When using a vise, you do not have to use a waster board under your stock.

• If you add a vise stop, you can repeatably add stock for milling the same part without any adjustments.

• In many cases, a vise can hold your stock more securely than table clamps.

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SERVO 06.2015

By Michael Simpson Post comments on this section and find any associated files and/or downloads at www.servomagazine.com /index.php/magazine/article/ june2015_Simpson.

Since I created the MF70 CNC conversion, I have received many requests for my workflow on creating parts. There are many directions one can take when building a part with a CNC machine. The exact workflow will depend on the CNC machine you are using, the part you are making, and the software you have on hand. I will break down some of my procedures into individual articles so that you can get an overview to my approach and possibly utilize some of the articles as a step-by-step guide.

The Vise Vises come in many Figure 2. shapes and sizes. Those shown in Figure 2 are just a few examples. Normally, you will size the vise to fit your machine and part.

You can use a small vise on a large machine, but you cannot use a large vise on a small machine.

Figure 3 shows a vise that is too large for the MF70 micro mill.

Not only is there no way to clamp the vise, the weight could possibly damage the MF70.

You are not limited to a single vise. Two vises can be used to hold long narrow stock as shown in Figure 4. If machining the ends of the stock using a single vise, it would chatter. By clamping it into two vises, it is held securely on both ends.

In this article, I will be showing you how to attach and tune the vise shown in Figure 5 to the MF70 micro CNC that we built in the April-August 2014 issues (however, the process is pretty much the same for any CNC machine). This vise was designed specifically for the MF70.

Figure 3.

Test Indicator While you need only a couple hand tools to attach the vise to the table, there is one tool you must have to adjust the vise properly. As a minimum, I recommend a dial Figure 4.

Figure 5.

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Figure 6.

Figure 7.

Figure 8.

indicator like the ones shown in Figure 6. For the best accuracy and ease of use, a test indicator is best. The indicator shown in Figure 7 has .0005 graduations, and its size and shape are perfect for aligning things on your Figure 9

machine. Also note the fully articulated arm shown in Figure 7. A single knob is used to hold the indicator in place once set. The magnetic base lets you easily attach to the cast iron used on most machines.

The Procedure While I am showing the procedure of mounting a vise on the MF70 using a test indicator, you should be able to apply what we do here to other machines and tools. This is a procedural process, so you will be doing it step by step.

Step 1 Attach the vise to the mill as shown in Figure 8. It should be about two inches from the end. The goal here is to have the working area of the vise plus a little overhead within the range of the CNC travel. At this point, just finger tighten the nuts holding the vise.

Step 2 Attach the test indicator to the CNC base as shown in Figure 9. The base on the MF70 is the only part that is

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Figure 11.

Figure 10.

made from cast iron, so itâ&#x20AC;&#x2122;s our only choice for attaching the magnetic base. On larger milling machines, I use the milling head as they are made from cast iron as well. Make sure you place the indicator base so the table wonâ&#x20AC;&#x2122;t hit the test indicator arm or base when it moves (Figure 10).

Figure 12.

Step 3 Position the test indicator probe on the leading left edge of the rear jaw as shown in Figure 11. I like to set the probe against the jaw, then move the indicator so that it is an additional 1/8â&#x20AC;? towards the jaw. This gives me the play I need to make adjustments.

Move the jaw to the right end (Figure 12) and back

Figure 14.

Figure 13.

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Figure 15.

Figure 16.

Figure 18.

Figure 17.

just to make sure it engages the jaw on both ends.

Step 4 Our indicator engages the jaw through the complete width of the vise. Make sure the indicator is on the left end of the jaw; slightly tighten the left nut on the vise as shown in Figure 13. Donâ&#x20AC;&#x2122;t make it so tight you wonâ&#x20AC;&#x2122;t be able to rock the opposite end of the vise for adjustments. Next, zero the indicator by rotating the bezel until the needle reads zero (Figure 14).

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Step 5 Move the table so that the indicator is on the right side of the jaw as shown in Figure 15. Be sure not to move the Y axis as this will throw off your adjustments. The reading shown on the indicator shows the degree of misalignment.

Move the vise with your hand until the indicator reads zero as shown in Figure 16.

Step 6 Once you are happy with the new position of the vise,

Figure 19.

Figure 20.

Figure 21.

slightly tighten the right nut (Figure 17). Again, only snug the nut as you may need to make adjustments on the left side.

Step 7 Move the X axis so that the indicator is on the left side of the jaw as in Figure 18. The indicator should read zero or near zero. If it does not, you will need to loosen the left nut and adjust the vise slightly, then retighten the nut and repeat steps 4-7.

Figure 22.

Step 8 Once you are happy with the readings on both sides of the jaw, tighten both nuts more securely. Once tightened, go back and check your readings once more to make sure nothing moved.

Vise Accessories Your vise is now in alignment with your table and ready for the stock. Figure 19 shows a piece of stock clamped into the vise. While exaggerated, it shows that it is nearly impossible to clamp a piece of stock into a vise without some sort of aid.

Figure 23.

Parallels Enter Stage Left A particular accessory solves this problem. They are called parallels. Figure 20 shows a small set of 1/4â&#x20AC;? parallels. They are precisely machined pieces of steel used to keep the stock parallel and raised for machining.

They are placed in the vise against each jaw as shown in Figure 21. The stock is then placed on the parallels and clamped in place (Figure 22).

In lieu of parallels, I often use thin neodymium magnets like the ones in Figures 23 and 24. Magnets are accurate enough, but will not replace a complete set of parallels. Parallels are sized for use with vises of different dimensions. You would not use a 6â&#x20AC;? long parallel on a 2â&#x20AC;?

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Figure 24.

Figure 25.

kit that came with the MF70 milling machine.

By using a vise stop, I can mill a part from the stock; once complete, simply remove the stock and add another without changing the setup. vise. I have a properly sized set of parallels for each vise I own.

Vise Stop One last vise accessory I want to discuss is the vise stop. Vise stops are used to index a piece of stock to one side or the other of a vise. These stops can be elaborate contraptions that connect directly to the vise or can be made from simple readily available parts.

The stop shown in Figure 25 is made from the clamp

Conclusion Vises are not only used on milling machines. Figure 26 shows one of the vises I use on my large KRMx02 CNC router to mill aluminum parts I sell on my website. The adjustment procedure is nearly identical to that of the one described here.

Next Month Next time, we will look at the tools and procedures I use to design a part.

Figure 26.

Final Thoughts If you want more information on my KRMx02, KRmc01, and KRmf70 CNC books, you can find them at www.kronosrobotics.com.

I also have a free download for an early CNC router book that I wrote. You can get it at www.kronos robotics.com/krmx01/ index.shtml.

If you have any questions, you can post them in the MF70 conversion forum located at http://forum. servomagazine.com/ viewtopic.php?f= 49&t=17107. SV

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Bots in Brief

Continued from page 15

JUMPING JERBOAS!

W

ho knew we needed a robotic jerboa? Apparently, the University of Pennsylvania did. A jerboa is sort of like a gerbil, except crossed with a kangaroo — at least as far as mobility is concerned. Jerboas bounce around on two absurdly long legs in what seems like a very dynamic and efficient type of motion — especially if you take the tail into account.

Avik De, a graduate student at the University of Pennsylvania, decided to try and build one based on the venerable RHex hexapod platform: “My first thought was to build a robot that runs like RHex on two legs.

So, full of visions of the running velociraptors in Jurassic Park, I set out to create a robot with a powerful tail and two RHex-like legs.”

Well, this is not really that robot. This robot only has actuated hips — not legs — plus a tail that it can move up and down. The legs have a spring, and by actuating the tail in a sort of anti-damping motion, the springs can be compressed causing the robot to jump due entirely to the motion of the tail. Basically, the tail is driving the legs.

The tail idea in general comes from UC Berkeley, but this is likely the first time a tail has been used in this particular way on a robot.

UPenn sees its jerboa robot as a platform that can be used to investigate all kinds of locomotion, including “sitting, standing, walking, hopping, running, turning, leaping, and more.” Based on what they’ve done with RHex as a research platform, expect some acrobatics.

Photo courtesy of UPenn Kodlab.

Photo courtesy of Cliff via Flickr.

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Basics of Soldering Part 4

By Bob Wettermann and Nick Brucks

Post comments on this article at www.servomagazine.com /index.php/magazine/article/june2015_Wettermann.

After discussing both leaded as well as SMT (surface-mount technology) soldering, we come to the final installment of this series where weâ&#x20AC;&#x2122;ll cover advanced SMT package soldering.

Ball grid arrays (BGAs) are a type of SMT package for integrated circuits that attach to the board using a grid of solder balls on the underside of the component. This allows for a large number of leads to make contact with a very small area of a printed circuit board (PCB), even compared to the most densely packed DIPs (dual in-line packages) and SOICs (small outline integrated circuits). In the electronics industry where miniaturization is key, this package style has proven easy to place with manufacturing equipment and has also been proven to be very robust in terms of longevity.

Figure 1. The removed device.

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Roboticists need a plethora of skills to create and construct their automatons. Knowing how to solder is a major part of moving from simple kits into the realm of advanced circuits and chassis.

Figure 3. Don't worry if there's a little excess paste on the stencil.

It can be easily wiped off with a lint free cloth.

Figure 2. Make sure the apertures of the stencil are properly aligned on the part.

Figure 4. If using a brush to apply alcohol, be careful not to scratch the PCB.

O

n the other hand, leadless devices — common types include QFNs [quad flat no leads] and LGA [land grid array] package styles — pursue miniaturization through a different route. Rather than attach to the board with any extended legs or leads, these devices make contact using solder “bumps” on the bottom of the component package. The place you will most

Figure 5. Make sure that the apertures are well aligned before you fully stick the stencil down.

often see these types of SMTs will be where very flat structure heights are required, such as in handheld devices or where a lot of heat dissipation is necessary.

However, the price of this compactness is that both of these component types are consequently difficult to place for hobbyists for single devices when there is no stencil printing involved. In addition, these packages generally SERVO 06.2015

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Figure 6. Generally, you'll want to place these components with tweezers due to their small size.

Figure 7. A good rule is to clean any PCB or component before soldering it since it is much easier to clean something with alcohol than it is to remove and replace a part because oils or contaminants interfered with the solder making good contact.

Figure 8. As with the leadless device, tweezers are very useful in placing stencils and components on a PCB.

require capital intensive/precision machines in order for them to be placed consistently. Because of this, instead of focusing on the initial placement of these components using the print and place process, this guide will instead turn an eye towards the hand prototype placement of such components.

Materials Needed: • Stencils • Solder paste

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Figure 9. As you did before, roll solder paste into the stencil.

• Isopropyl alcohol and lint free wipes for cleaning the stencil • Solder wick • Miniature squeegee • Reflow source — either a heat gun or a reflow oven As always, remember to take the necessary ESD and safety precautions to avoid any potential hazards to you or to the components mentioned throughout this series.

Let’s start with leadless component repair. Once you’ve picked up the part, you will want to use a QFN stencil to

place the bumps on the bottom of the component, since doing this manually is time-consuming and difficult to be accomplished at an even height — even for trained technicians.

1. To get started, clean off contaminates on the lands of the device.

2. Place the larger of the two stencils, with the part lands properly aligned with the apertures of the stencil.

3. Squeegee solder paste into the apertures of the stencil. Using the squeegee, scoop a little solder paste out of the container, then starting at one side roll solder paste into the apertures by moving the squeegee to the opposite side of the stencil.

4. After wiping off any excess solder, reflow based on the type of solder you are using. It is recommended that this be done by running the assembly through a reflow oven (toaster oven with controls will work).

However, a heat gun can also suffice.

5. Remove the stencil from the device and clean off the part lands using isopropyl alcohol. You should see uniform and consistent solder bumps on the lands.

6. Now, prepare the board that the device will be placed on by using isopropyl alcohol.

7. Place the board stencil onto the PCB. We used a StencilMate™. Once it is properly aligned, apply pressure to the stencil to stick it in place in order to activate the adhesive. Make sure that the apertures line up with the lands before you do this because once the stencil is stuck down, it cannot be removed and reused. To make any changes after this point, you will have to start over.

8. As before, squeegee solder paste into the stencil.

9. Place the bumped device into the stencil. Reflow again using the same profile to reflow the solder paste.

10. Inspect the final product for any anomalies. Make sure that the part lies flat and hasn’t been damaged in any way by the heat. Unfortunately, due to the nature of the leads of the component, inspecting the underside to check for good solder contact is difficult. Often, the only way to truly know if it works is to test it.

When it comes to placing BGAs, the main issue you will see is the problem of placing fine-pitched devices and having solder joints which cannot be visibly inspected from the solder ball to the land.

1. Clean the site using isopropyl alcohol to get rid of any contaminants that might interfere with a good solder joint.

2. Peel the adhesive backing off of the stencil.

3. Align the stencil. The most reliable way to do this is to line up diagonally opposite corner apertures over

Figure 10. For a part of this size, it is most likely easier to just place it by hand rather than with tweezers.

their corresponding lands.

4. Once you’re sure the stencil is well aligned, place the stencil starting at one corner and slowly work towards the opposite corner. Smooth down the stencil afterwards to remove any air bubbles. Apply pressure to activate the adhesive.

5. Squeegee solder paste across the top of the stencil.

Make sure paste has been rolled into all of the apertures.

6. Wipe off any excess solder paste on top of the stencil using a lint free wipe.

7. Gently place the BGA. Make sure the balls or leads of the component of the part are aligned with the apertures.

8. Reflow the part either using a toaster oven or a heat gun.

9. Inspect the BGA to make sure it is level and look under the component to ensure that none of the solder balls are cracked or bridged in any way.

Through this series of articles, we hope you’ve acquired a few new skills to help you in your projects. These guides should at least provide a solid base on which to build more advanced soldering skills, or simply to do a little rework or repair from time to time. Regardless of what you choose to use these skills towards, we trust you have learned something of value. SV

SERVO 06.2015

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SERVO 06.2015

69

Twin Tweaks

by Bryce Woolley and Evan Woolley

The Force Servo Arm Awakens

T

he namesake of this magazine is the humble workhorse of the robotics world. Servos may not normally be flashy or glamorous, but they are essential building blocks for a panoply of mechanisms ranging from drive trains to endeffectors. The reason for the servo’s ubiquity is the elegance with which it solves an essential problem: moving something to a certain position. Sometimes, you want to do more than just move something to a certain position. Sometimes just setting a servo-powered claw to a closed position will end up putting something like a Darth Vader force choke on whatever hapless object you want to pick up. If that object is fragile, then whatever task you were hoping to accomplish is as doomed as the Death Star after the rebels discovered its fatal defect.

The Force servo arm — available from ServoCity — hopes to solve that problem. The compact device sits atop a servo in place of a regular horn, and allows you to position the servo according to the force it exerts. Not only is the force strong with this device, it can be weak too — if that’s what’s needed to avoid crushing fragile cargo.

These are the Sensors You're Looking For The Force servo arm (designed by Aleksey Zaitsevsky) is

THE FORCE SERVO ARM FROM SERVOCITY.

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SERVO 06.2015

Disclaimer: If you are not a Star Wars fan, please forgive the plethora of puns. a compact device made up of an ABS body roughly pentagonal in shape, with what appears to be some force sensitive resistors and a small PCB (printed circuit board). A PWM cable extends from the PCB and promises easy integration into your servo-based projects. The underside of the device features a counterbored spline cut hole for fastening to a 25-tooth spline — like you find on a standard Futaba servo. It comes with a screw for attachment to a servo drive shaft. The pointed end of the ABS body contains four 2 mm diameter mounting holes, spaced 5 mm apart.

The Force servo arm is designed to take the place of a potentiometer in a standard servo. Servos work based on the principle of negative feedback — kind of like when Luke was parrying with the orb-shaped training remote and getting a little blast every time he failed to trust the Force.

The controller will send a (control) signal to the servo based on what position the user of the program selects. As the motor (and gearbox) turns, the position of the potentiometer (which is connected to the gearbox) is checked against the control position. If it doesn’t match the control position, the motor keeps turning. When the signal from the potentiometer matches the control signal, the position has been reached and the servo stops.

At the core of this feedback loop is the potentiometer.

A potentiometer is a small device that looks like a knob, and the knob can turn over a limited range. The potentiometer works like a variable voltage divider, and when the knob turns it is effectively changing the resistance of the second resistor in the voltage divider. Thus, the change in the output voltage from the potentiometer corresponds to the rotational position of the servo.

The Force servo arm takes the place of the potentiometer. The specs on the Force arm are a bit mysterious like the crossguard lightsaber-wielding Kylo Ren. The product manual on the ServoCity website provides plenty of detail on the physical design of this, with thoroughly annotated dimensions and other structural details. There is not much detail, however, on the circuit used for sensing force. The secrecy may be due to its status as a patent pending invention, with the application not having been published.

Visual inspection of the device reveals what appear to

Twin brothers hack whatever’s put in front of them, then tell you about it.

Go to www.servomagazine.com/index.php/magazine/article/june2015_TwinTweaks to comment on this article.

FUTABA

GEARBOX.

EXPOSING THE PCB.

be a couple of force sensitive resistors as mentioned previously. Force sensitive resistors are made up of a conducting polymer that changes resistance as pressure is applied. The resistors are nestled inside of a cutout section in the pentagonal body, and they flank the center mounting hole for the servo drive shaft. The body section containing the center mounting hole looks a bit like a peninsula jutting out into the center cutout, and two somewhat cloudy looking blocks extend from the edges of the center piece to the walls of the cutout. The resistors are positioned partially underneath the cloudy blocks. It’s a very clever design.

As the main body of the device presses against something, the cutout causes the body to flex about the servo drive shaft. The cloudy blocks transfer the force to the resistors, and the device sends out a changing voltage corresponding to the force exerted on the resistors. It’s an elegantly compact device — like everybody’s new favorite spherical droid, BB8.

I Find Your Lack of Continuous Rotation Disturbing Implementing the Force servo arm is not quite as simple

as slapping it onto a 25-tooth servo spline. Well, it can be that simple if you have the right servos — ones that don’t have a potentiometer and already have an extra PWM cable waiting for whatever device will replace the missing pot.

Such servos include the MKS DS6630 and other MKS servos normally used for camera gimbals.

If you don’t have these specialized servos, it just takes a few modifications to enable a servo to work with the Force arm. In fact, modifying a servo to interface with the device is an operation very similar to a fundamental hack that is as essential for any roboticist to master as self-control for a Padawan training to become a Jedi knight: modifying a servo for continuous rotation.

Generally, servos rotate over a limited range — potentiometers themselves have only a limited range. To enforce the limited range, the gearbox on a servo includes a pin on one of the gears. Confined to a slot, the pin stops the gearbox from turning beyond the determined range.

In many instances, it is useful to modify a servo for continuous rotation. With their compact size and high ratio gearbox, servos can make a great motor for small robots for use either in a drive train or in mechanisms like arms. For the Force servo arm — since you’re replacing the potentiometer — you’re already halfway to continuous rotation.

Taking out the stop is also essential because the Force servo arm would not sense any force from the stop when the gear reached the limit of its range — the force would be acting on the gearbox and not the arm.

Without any force acting on the arm, it would keep going until it encountered the force it was FUTABA PCB looking for. It would never hit its WITH VOLTAGE DIVIDER. mark, like a Stormtrooper firing his blaster and never ever hitting SERVO 06.2015

71

PREPARING FOR THE POTENTIOMETER -ECTOMY.

READY

FOR REASSEMBLY.

wouldn’t budge much.

After desoldering the motor leads, on most servos you the target. In the meantime, the gearbox would be can extract the PCB — at least for a certain distance. The struggling against the stop, and you would risk burning out potentiometer is often screwed into the bottom of the the motor. gearbox, but the pot is usually connected to the PCB via The difficulty of the continuous rotation modification some wires that at least give you enough leeway to pull out depends on the servo you’re working with. ServoCity the board a good distance. The Savox PCB, however, was as provides a very helpful “Rotation Modification Difficulty immobile as Jabba the Hutt nestled comfortably on his dais.

List” that ranks servos on a scale from 1 to 10, with 1 We were able to peek under the PCB enough to find the being the easiest and 10 being the hardest. Modifications culprit. Instead of connecting to the PCB with flexible wires, are deemed more difficult where more soldering is the pot was soldered directly into the PCB and, in turn, the required, where the stop in the gearbox is metal instead of pot was screwed into the bottom of the gearbox with not plastic, and whether the spline needs to be drilled out. one, but two screws.

To give ourselves a few options as far as what servos to The pot leads were flexible enough to give us room to use with our servo arm, we set out to modify a few servos slide in a small screwdriver and remove the two screws for continuous rotation. We selected a servo from Hitec holding the potentiometer in place. Once you get the PCB (the HS 322), one from Futaba (the S3003), and a servo free, the next step is to desolder the potentiometer. For from Savox (the SC-1258-TG). We started with the Savox. other servos like the Hitec, we were simply able to desolder Savox servos are high-end, with an all-metal construction the wires from the pot, leaving the connections to the PCB and serious torque. We previously worked with them back unscathed. With the Savox, we would have to perform in the July 2011 issue, where we equipped an off-roading some precise solder surgery. bot with a Savox servo for its steering mechanism.

The three leads were very securely soldered into the The first step for a continuous rotation modification is to PCB and a challenge to remove. It was a situation almost as remove the bottom plate of the servo. Generally, servo sticky as being trapped in a garbage compactor in the casings are held together with four long screws that can be underbelly of the Death Star. With some helping hands and removed with a Phillips head screwdriver. Be careful when our trusty solder sucker, we soon liberated the you remove the screws because they are also what hold the potentiometer. top park of the casing and gearbox in place.

The manual for the Force servo arm suggests wiring Once the bottom plate comes off, the servo PCB will the device directly into the servo PCB. We preferred to keep be exposed. The potentiometer is hidden under the PCB, so our options open, so instead of soldering the arm directly it has to some out. The circuit board is usually fixed in into the PCB, we soldered a PWM cable into the PCB that place, mainly by the leads from the motor. The motor leads would, in turn, connect to the device. With the cable are easily identified as they are soldered in place, we were normally the only connections ready to move onto the REALLY GRINDING MY GEARS. on the PCB slathered in so gearbox. much solder they looked like Han Solo’s hands poking out from his carbonite storage.

Our trusty solder sucker made the desoldering process In all of the servos we’ve quick, but the PCB still modified for continuous

Now, This is Servo Hacking

72

SERVO 06.2015

REMEMBER THIS ASSEMBLY!

THE

MANUAL DUAL SERVO DRIVER FROM

SERVOCITY.

rotation, the potentiometer could come completely out but we did need to make one change to the PCB. without affecting the operation of the gearbox. Other When modifying a servo for full rotation, you remove servos might require further modification, like drilling out the potentiometer like we had been doing here, but instead the spline. Fortunately, that wasn’t something we had to of replacing it with a device like the Force servo arm, all you worry about with the Savox, Hitec, or Futaba servos. need is a simple voltage divider comprised of two resistors.

We turned the Savox servo right side up and carefully By replacing the pot with a voltage divider, the servo removed the top casing. Be careful not to accidentally take sends back the same position no matter how far the horn apart the gearbox as you take off the casing — you’ll want has rotated. Since it will never reach that position because to see how everything fits together so you can put it all the resistance of the voltage divider won’t change, the back together once you’re done. Taking a picture is a good servo will rotate continuously. It’s a good idea to set the way to give yourself a guide for reassembly. voltage divider to the middle of the range of the pot Take apart the gearbox, taking care to keep the gears because the resistance of the divider will set your neutral clean, and you’ll find one gear with a stop on it. Many position. A common value for the pots found in servos is 5 servos have plastic gearboxes, so the stop can be easily kΩ, so divide that by two to get your ideal neutral position removed with some flush cuts. The Savox servo, however, of 2.5 kΩ. was equipped with titanium gears, which are not exactly To make the voltage divider as easy as possible to susceptible to hand cutters. To shave down the metal stop, construct and fit on the PCB, you’ll want to use as few we busted out our trusty rotary cutter. We secured the gear in a vice and shaved down the stop until it was flush with the gear.

With the potentiometer and gear stop both as gone as Alderaan, we were ready to put the servo back together. Our last modification would be to cut the casing to allow the second PWM cable an escape route next to the original cable. Our rotary cutter made quick work of the mod. We reassembled the gearbox with reference to our picture, put the top casing back on, flipped the servo around, resoldered the motor leads, and reattached the bottom casing.

The Hitec was easier to modify. The pot was held in with only one screw, and it was soldered to the PCB via some wires that we connected to a PWM cable. The gears were plastic, and we were able to snip the stop by hand. The Futaba was even easier to ACTOBOTICS PARTS. modify because we had previously modified it for continuous rotation. The gearbox was ready to go, SERVO 06.2015

73

IMPLEMENTING THE FORCE SERVO ARM.

SENSING A DISTURBANCE IN THE FORCE.

resistors as possible. The closest you’ll get with two readily available resistors is to use two 2.2 kΩ resistors. One end of the voltage divider goes to power, one to ground, and the middle of the divider goes to the signal pad. The Futaba servo had just that kind of voltage divider in place, but we were forced to dispose of it as mercilessly as Boba Fett dispatches his bounty. We soldered the PWM cable leads into its place, and that gave us three continuous rotation servos to choose from.

The Force is Too Strong with This One

PARALLEL

GRIPPER.

READY

FOR CLAMPING.

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SERVO 06.2015

With the servos and Force arm ready, we needed a robot to test them with. Fortunately, ServoCity had us covered in that respect too — we would make a testing robot out of Actobotics pieces.

One of our least favorite parts about working with servos over the last few years has been the challenge with interfacing them with structural units. Servo horns are often made of thin plastic and dotted with oddly patterned holes.

Drilling mounting holes on structural parts for use with servos can be a tedious process because even after meticulously measuring the placement with calipers, marking the location with a center punch, and carefully positioning your drill, if the bit walks even a little smidge your tiny mounting hole meant to accommodate a tiny screw will be as effective as C-3PO is at being rude.

Actobotics solves that problem by providing structural parts with a unique overlapping hole pattern designed to align perfectly with servo horns. In addition to the structural bits (made from aluminum and heavy on the cool factor), Actobotics also boasts gears, motor mounts, bearings, and everything else you might need to build an awesome robot.

Some of the Actobotics parts that caught our eyes were the gripper kits. A robot with two claws would be a perfect way to test the Force servo arm — one claw would be equipped with a normal servo, while the other would use the Force arm. We anticipated that the normal servo would be capable of gripping durable objects effectively, but when tasked with picking up something fragile it would

CLOSED

POSITION

=

CRUSHED BERRY.

crush the object without being reprogrammed. The Force servo arm, however, would need to be set only once to grab objects of varying sizes and fragility.

Before building up our robot, we wanted to test the Force servo arm with the modified servos. ServoCity offers a very useful manual dual servo driver which has two knobs for controlling two servos, and a connection for a battery pack. We scrounged up a battery pack, connected the Force arm to the servo, then connected it all to the box. We started with the Force servo arm loose and not attached to the servo spline. We pressed the center section of the Force arm by hand to simulate it pressing against something, and we were delighted to see the servo slow to a stop.

It worked perfectly with the Hitec and Futaba servos, but the Savox was less cooperative. Upon further inspection, we discovered that during the desoldering process we had inadvertently destroyed the solder pads on the PCB, so the torque servo would have to sit this one out.

After successfully testing the two other servos, we were ready to build our robot, starting with the two grippers. In lieu of traditional paper instructions JUST A GENTLE included with the parts, the gripper SQUEEZE. instructions come in the form of an instructional YouTube video linked to on the ServoCity website. The video is well produced with a low-key narrator, clear identification of the parts you use for each step, and good close-ups to help you gauge your accuracy. The toughest part about assembling the gripper arms has to do with mounting the servo.

As part of its compact design, the gear arms are basically flush with the base plate, and they sit right above the servo. This means there’s no room for nuts or bolt heads. The clever design solution is to have the screws thread into the base plate. The only problem is that the base plate isn’t threaded for the

YOUR

FRUIT SALAD IS RUINED.

7/16 screws used to mount the servo, so the user has to cut the threads into the ABS the first time the servo is mounted.

One word of caution here is to be careful not to strip out your screws as you are cutting the threads into the ABS. We suggest threading the holes before your first assembly. To give yourself the best chance to thread the screw perfectly normal to the plate, we suggest pressing the plate against a flat surface and using a large screwdriver. The thicker handle will give you better toque, and the flat surface will help you make sure the screw stays vertical.

The grippers came together smoothly, and we built up a simple base for the arms. Both grippers clamped down nicely on a screwdriver for our first test. The best fragile things we had handy to test were blueberries — besides, who doesn’t want a robot to help them with making a summer fruit salad? As expected, the normal servo crushed the hapless berry as it moved to a closed position. The Force servo arm, on the other hand, gently squeezed the berry but did not crush it. It was equally suited to gripping durable screwdrivers and fragile berries without reprogramming.

The Force servo arm is a compact and elegant device that can help you add cool capabilities to any servo. Taking advantage of those capabilities was easier than ever with Actobotics. When it comes to delicate end-effector operations, the Force servo arm frees you to stick with Obi-Wan’s advice and trust the Force. SV

Recommended Websites www.servocity.com www.myresearch.company/ f-servo.phtml SERVO 06.2015

75

a n d

g{xÇ Now

by Tom Carroll TWCarroll@aol.com

Prototyping and Building a Robot I've written about the design process for amateur robot builders in this column, as well as tried to answer the question, “What does it take to build a robot?” Most of the queries I receive when talking with prospective robot builders seem to revolve around the mechanical and construction aspects of robot design. It could be these people realize that I am not the sharpest programmer on the planet and just steer conversations to mechanical or electrical system topics. I can compare PICs, Arduinos, Propellers, and even Raspberry Pis, but try to steer away from writing lines of code and leave that to friends who are far better than me. n the December 2014 issue, I covered the larger overall aspect of robot design. After reading that article, several people have asked me to go into more detail on just the structural and mechanical aspects of robot design.

With that in mind, I am not going

I

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SERVO 06.2015

into microcontrollers and programming, CAD design, or even electrical and sensor systems. I will discuss the physical placement of these components as part of an overall robot design.

I want to concentrate on how a robot experimenter can develop and refine his or her robot’s mechanical design using prototyping methods. I’ll leave the final robot’s design to you.

We will look at mounting components, systems, motors, and batteries to create an efficient platform and a stable center of gravity. I will also refer to ServoCity’s Actobotics line of mechanical and structural components as examples of available systems. Their website contains thousands of photographs of mechanical assemblies that give many examples and ideas of robot construction.

I will also discuss other structural members and mechanical parts, as well as basic machining practices. I’ll show some examples of other mobile robot platforms available on which an experimenter can build a nice robot.

a great reason to build a robot.

Cool means that the person wants to learn something different, and finding out about robots and building is a great way to start.

Depending on their background, knowledge base, and ultimate goals, what type of robot they build might come a bit later.

Quite a few people I talk about building a first robot with take my suggestion and buy one of the small Parallax robot kits such as the ActivityBot (Figure 1) or the original Boe-Bot, which range from $150 to $199. They are one of the least expensive ways to enter into the field of robotics, and the course manual that comes with these kits is second to none.

These desktop robots can be configured in so many ways with grippers, sonar, line following, cameras, Xbee, Bluetooth and Wi-Fi connectivity, and even speech and speech recognition. Even the less expensive, ready-built Parallax S2 is hackable.

Initial Robot Design — the Ready-Builts I always answer a robot building question with: Why do you want to build a robot and what do you want it to do? I begin with “why” as many people really do not know why. They just feel that “building a robot would be cool.” Actually, that is one of the best answers to why. “Cool” is

Figure 1. Parallax ActivityBot.

Advances in robots and robotics over the years.

Post comments on this article at www.servomagazine.com/index.php/magazine/article/june2015_ThenNow.

Figure 2. ServoCity ActoBitty robot.

Figure 4. Parallax Eddie — Windows-based robot with Kinect sensor.

Figure 3. Parallax original 2010 plywood base.

The mechanics are simple enough so as not to scare away those who fear such, and the programming — especially the Propeller-based ActivityBot’s “C” programming — is simple to learn, but sophisticated enough to control a very complex robot later on.

For a bit tighter budget, the ServoCity ActoBitty at $27.99 (Figure 2) includes two gearmotors with wheels, a four AA battery holder, a 41/2” aluminum channel chassis and clips for an Arduino, and the battery box. It is a quality build and the price can’t be beat for a starter robot at

around $50 total.

The robot shown here has an Arduino and line follower sensors attached. As with the more expensive ActivityBot, a builder can add whatever they might want in developing a future larger robot.

Some robot enthusiasts have started with the Boe-Bot series and maybe have also used LEGO Mindstorms, VEX, or similar educational kits. All of these use simple mechanical construction, and many experimenters want to make the next leap to constructing their own robots. They feel confident enough to

tackle the construction of a robot’s base with associated structure to hold sensors, arms, drive systems, and batteries. This is the level that I want to discuss in this article.

The Ultimate Use of Your Robot Let’s assume that you have built a couple of small robots and are ready to tackle building your own. You can break down types of robots in which you might have interest into an educational test bed, a robot for the home, an outdoor robot, a combat robot, a medical assistant robot, or one of many other types. There are many more categories of robots and each can be broken down further into sub-categories, but I will just lead off with these.

Many experimenters I have spoken to want to use their robot in many ways. Maybe you just want to start off with an expandable mobile platform on which you can add all SERVO 06.2015

77

Figure 6.

Multi-level base by RobotElectronics in the UK.

Figure 5. Willow Garage TurtleBot using iRobot Create base and ROS.

sorts of sensors and appendages, and then modify and change it at will for learning purposes.

Many times, the robot’s design ends up being driven by what materials are available, but you can steer the design a bit to incorporate your particular needs.

processing. Parallax used multiple levels of HDPE stout plastic of the same design and shape as the original plywood base. This was carried over to the present Arlo base that Parallax sells today.

At about the same time, Willow Garage developed the TurtleBot shown in Figure 5 that also utilized the Kinect sensor, but used ROS (Robot Operating System) for program development. A multi-level robot base shown in Figure 6 made by Robot-

Educational Robot Platform You can look at some already manufactured robot designs as a sample idea from which you can design your own. Parallax has been building robots since the first Boe-Bot I mentioned earlier.

In 2010, President Ken Gracey realized that his customers were interested in larger robots, so he looked at using high quality nine ply furniture grade plywood for the robot base shown in Figure 3.

The Kinect based Eddie robot designed by Parallax shown in Figure 4 required a laptop on the top platform using Windows for the image

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SERVO 06.2015

Electronics in the UK is another similar robot platform.

These four robot bases represent a great mid-sized robot design. They are round (or roundish, in the case of the UK robot) and are differentially driven for easy control and tight steering.

More importantly, the large upper platform can hold an open laptop to view the screen, or you can slip a closed laptop into a lower ‘slot’ to allow an open sensor or experiment area on the top.

Even the smaller diameter TurtleBot that uses the iRobot Create base allows the use of a compact notebook computer as a higher-level microprocessor in the place of a microcontroller. The round differentially driven style is one of the best robot designs for most experimenters.

Building Your Own Robot Base

Figure 7. Parallax drawing showing precision cutouts for robot base.

The robot’s base is the most important part of your project. Whether your robot contains a hollow shell for a lot of its structures or to have all the components mounted on the base, the base still supports the whole robot.

The drawing from Parallax in Figure 7 shows

how holes were cut for the drive motors, as well as the two drive wheels. The fore and aft casters allow quick manueverability with the differential steering system. You might desire two levels (platforms) on which to place a computer, Kinect sensor, video cameras, and other sensors.

Most people like to place their batteries at the lowest point for stability, such as below the bottom level in the Parallax Eddie. This is fine for heavy gelled electrolyte lead-acid batteries, but lithium-ion and especially lithium polymer batteries should be placed in a higher, easily accessible location.

So, we’ve talked about a few different types of bases for robots that are offered by several good robot manufacturers, but it can be easy to build your own. For smaller robots, it makes sense to use an already-built platform, but you can save money by building bases for larger robots yourself.

We have already seen that plywood can make a pretty good platform — even if you cannot find the quality plywood that Parallax used in their initial large bases.

All of my earliest robots were made of plywood or galvanized steel HVAC ducting. Depending on the overall size of your design, anything from 1/4” to 1” plywood (with both sides smooth finished) will do.

Figure 8. The 1.5” x 1.5” aluminum channel stock from ServoCity.

In later years, I preferred metal bases for larger robots, and have used 1/8” and 1/4” 6061-T6 aluminum for most of my creations.

If you are limited to just thin metal stock, a great design concept is to use Actobotics 1-1/2” x 1-1/2” aluminum channel as shown in Figure 8 as side rails to strengthen the flexible sheet metal, as well as for mounting motors and wheels.

You can also use shorter channels for the front and back, as there are 10 lengths to choose from.

The advantage to these channels over stock “L” or aluminum channels at hardware stores is the unique hole patterns that fit so many ServoCity products and brackets. The robot shown in Figure 9 was built by Robert Beatty and his daughters, and was made entirely from Actobotics channel stock.

Figure 9. Robot built by Robert Beatty and his daughters with Actobotics channels.

Working Metal Structures for Your Robot Project For many years, I had access to large power metal shears for cutting and metal brakes for bending metal sheets. I no longer have this access like many other people, so must resort to purchasing metal pieces already supplied in the sizes required. Of

Figure 10.

Inexpensive horizontal/vertical bandsaw by Northern Tool.

Figure 11. Milwaukie Sawzall cutting steel channel.

SERVO 06.2015

79

Figure 12. Dykem marker used on sheet metal to layout lines to cut.

course, you can cut smaller sizes from a larger piece. Handheld metal nibblers, ‘tin snips,’ and even hack saws can be used in metal cutting.

Many people use a combination horizontal/vertical band saw such as the $250 one shown in Figure 10 from Northern Tool. Less expensive ones like this sometimes have a ‘wiggly’ base, but still cut metal just fine. In a pinch, I have used my trusty Milwaukie Sawzall to cut about 75” of 1/4” aluminum plate with a single blade. Yeah, it’s thought of as a demo tool, but that sucker can cut anything (Figure 11).

Use a medium speed, keep moving the saw at a steady pace, and cut close — but not too close — to your scribed line. Place some masking tape on the saw’s shoe to keep the vibration from scarring the metal, and sand or file edges smooth after the cuts. The straighter your cuts, the less sanding and filing will be required.

Using a bench belt sander for straight edges will make the job go faster.

Some robot builders like a fixed vertical band saw since they usually have a larger cutting radius, but metal cutting versions cost a lot more, as do larger combo saws.

Use a compass with a metal scribe for circles, or make a cardboard or plastic outline guide and trace out your part’s shape on the raw metal with a scribed mark.

I like to use Dykem — a blue dye that makes the scribed marks very visible as in Figure 12. Make your scribe marks deep enough in case you accidentally rub off some of the Dykem dye.

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For cutting round bearings in the gearbox holes up to about 3” in to take the bending metal, I like to use hole moment, but many saws or fly cutters in a gearmotors that a drill press as shown in prospective robot builder Figure 13. I cannot might find in a catalog stress safety enough do not have dual when using any power bearings on the output tool, but especially saws shaft. and drill presses. If all of Most times, you the parts of a fly cutter cannot determine this are not properly cinched when you buy a Figure 13. Fly cutter in down, you may find the gearmotor online or drill press to cut circles in metal. cutter embedded in your even at a store where chest or eye socket, and you can handle the that includes the drill press chuck key gearmotor. To be sure, either view the that you left in when you turned the company’s datasheet or just open the drill press on. Wear safety glasses! gearbox and verify that the back of If you are a newbie in metal the output shaft has a ball bearing work, I suggest you learn basic mounted in the back of the case, and machining and safety practices from another ball bearing in front of the an experienced friend or at a local final gear supported by the front of community college. Any of the tools the case. Bronze bushings can be that I’ve mentioned can be your best substituted, as well. friend in helping you build great robots inexpensively. Or, they can be your worst enemy when you don’t use safe practices and end up in your local Robot builders sometimes feel hospital. that “the more wheels on their robot, the better.” In most cases, that is not true. Not only do more wheels require more drive motors if they are to be driven, but also require more If you have designed a robot mounting hardware. base, more than likely you are going Figure 14 shows a completed to make it a mobile robot. With that Nomad robot from ServoCity before in mind, you’ll be using some sort of the addition of wiring, batteries, and wheels — anywhere from two to six or control systems. Notice how the right more. Maybe you’ll use treads or even channel holding the two drive motors legs, but I’ll “steer” my discussion and wheels is canted to allow fourmore towards wheeled robots. wheel contact with the concrete.

It is always tempting to mount Only one of the channels moves your wheels directly on your drive gearmotors, but that is not always the best thing to do. It works just fine to use wheels mounted on model aircraft type servos on very small robots such as in the less than one pound category, but not for larger robots.

The output shafts for most gearmotors are designed to withstand twisting torque loads but not very much bending moment. Certain large Figure 14. ServoCity Nomad 4WD off-road chassis showing canted gearmotors that are used for electric wheel assembly. wheelchairs are designed with two

Mounting the Wheels

Mounting the Robot's Drive Systems

Figure 15. ServoCity HD planetary gearmotor with 'mount C' attached.

up and down. This works well for an off-road 6-1/2 pound robot like this that is operated on rough surfaces.

I have a Nomad that I first configured for R/C control and it really zips along, and actually did a complete flip in the air and landed back on its tires when it ran over a rock. (I never could get it to do it again, though.)

In the case of a four, six, or even an eight wheeled robot, unless you have taken into consideration having the fore and aft wheels driven similar to an Ackermann (car type) configuration, you will have friction generated when your robot steers.

Friction eats up valuable onboard energy.

Six wheels might help your robot traverse a rough rocky terrain, but the fore and aft wheels should be steered for the turns, and each wheel should be sprung to compensate for uneven surfaces. Unless you are after a true off-road robot, a multitude of wheels might look ‘cool,’ but efficiency and functionality beats cool any day.

Mounting the robot’s wheels can be as simple as fastening the drive wheels onto a dual-bearing gearmotor. However, many times we come across a ‘perfect’ gearmotor that has the speed and torque that we require for a robot design as well as the correct voltage and high efficiency, but — as I mentioned above — cannot take the side loads created by mounting a wheel on it.

Planetary gearmotors usually have a geartrain that is similar in cylindrical diameter as the motor, and have face-

Figure 16.

Spring-loaded Wheels for Parallax ARLO Platform

mounting threaded holes for fastening to a flat surface. The ServoCity HD planetary gearmotor shown in Figure 15 is a good example of a type of motor that is easy to mount.

To take wheel loads off of a gearmotor’s shaft, the use of a chain drive can be employed. This method can serve another purpose in that using two different sizes of chain sprockets can allow the builder to use the gear ratio to increase or decrease the final wheel speed and compensate for the inability to locate a motor drive with the ideal output speed.

Again, look at ServoCity’s website www.servocity.com to peruse the many hundreds of photos of sample structural and mechanical systems applications.

Another key issue in building robots with two differential drive motors and wheels is the possibility of accidentally having the drive wheels ‘high sided’ by a door sill or uneven ground. This can occur when the robot has two casters: one in the front and the other in the rear. The use of a single caster will not cause this problem.

When the front or back or both casters end up on a slight rise, the main drive wheels can be left not touching the floor or ground, thus stranded.

More than likely, the robot will tilt to one side being balanced on the two casters, and one of the drive

wheels will more than likely drive the robot onto a level surface.

I have worked with Parallax to develop a spring-loaded caster wheel assembly (shown in Figure 16) to alleviate this problem. To utilize this type of caster, the builder should have several ‘strengths’ of springs available, depending on their robot’s weight.

A spring too strong can push the robot up just as if there were no spring. Use a spring too soft, and the robot will end up wobbling too much over uneven terrain, and wobbling back and forth when starting and stopping.

Final Thoughts There is no ‘best’ way to design a robot. There are so many issues to take into consideration when building bots. I can safely say that using some of the prototyping materials from ServoCity that I’ve discussed here can really help a robot builder who does not want to take the time to machine or have parts machined for their robot.

There are also the various educational robot kits from VEX, Parallax, MINDS-i, LEGO, Tetrix, and others that are great for teaching robotics concepts. Sometimes you just need a little inspiration from existing products to get you on the path to designing your own. SV SERVO 06.2015

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Zumo 32U4 High performance in an accessible robot Powerful and versatile, the Zumo 32U4 is a mobile

robot

accessible

to

beginners

yet

engaging for advanced users. The integrated ATmega32U4 offers Arduino-compatible support for those getting started with electronics and microcontrollers, while advanced features include quadrature encoders, a sophisticated object detection system, and an inertial measurement system (IMU), enabling substantial educational and research applications.

Whether you want a competitive Mini-Sumo robot, a robot swarm, or a small friend to roam your desk, the Zumo 32U4 is the robot for you.

Find out more at www.pololu.com/zumo