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Bangladesh University of Engineering and Technology Department of Mechanical Engineering
Instrumentation and Measurement Sessional Course No: ME-362
Project Title: Terrain Hazard Optimized Robot (THOR)
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Supervised by: •
Dr. M.A. Taher Ali o
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A.K.M. Monjur Morshed o
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Lecturer Dept. of Mechanical Engineering,
Md. Al-Amin Khan Chowdhury o
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Assistant Professor, Dept. of Mechanical Engineering
Md. Wasim Akram o
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Professor ,Dept. of Mechanical Engineering
Lecturer, Dept. of Mechanical Engineering
Abdul Motin o
Lecturer , Dept. of Mechanical Engineering
Presented by: Group A 15 Roll No
Student Name
0510005
Naser Imran Hossain *
0510014
Md. Rokanuzzaman Khan
0510024
Prajnaprasun Bhattacharjee
0510033 Dept: Mechanical Engineering Level- 3/ Term-1
Nahid Pervez
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Acknowledgements From the first day we started our journey as engineering students, we’ve gone through many prescribed courses. But very few were as challenging or unique as this course. We came across a plethora of new terms, instruments, technologies and scientific observations that we had never had the pleasure of familiarizing ourselves with. Without the help of our experienced course teachers, we could’ve never made it through this challenging endeavor. So, we would like to thank the following teachers for their diligent help:-
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Dr. M.A. Taher Ali o Professor ,Dept. of Mechanical Engineering
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A.K.M. Monjur Morshed o
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Md. Wasim Akram o
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Lecturer, Dept. of Mechanical Engineering
Md. Al-Amin Khan Chowdhury o
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Assistant Professor, Dept. of Mechanical Engineering
Lecturer, Dept. of Mechanical Engineering
Abdul Motin o
Lecturer , Dept. of Mechanical Engineering
We would also like to mention MR. MASUDUR RAHMAN (Asst. instrumentation engineer), who gave us his utmost help throughout the course and provided necessary technical instruction whenever we faced any obstacles in accomplishing our project.
4 Finally we want to thank all the lab assistants of our carpentry shop and machine shop for their continuous help though out the term in all possible ways.
Abstract: The Terrain Hazard Optimized Robot (THOR) is a rover like robot controlled manually to navigate through uncharted and possibly hazardous environment. Thus the nomenclature. It is designed to vertically lift or place mission objectives with its custom designed gripper arm and afterwards move through difficult terrain taking advantage of its pseudoholonomic drive and high-torque mechanism. It has a two story structure, with one supporting the power units and the driving motors and the other with the arm-base and gripping motors. As an additional recon measure, sensors have been used to give THOR a sense of heat and light.
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Contents 1. Introduction ................................... .................................................... 6 2. Objective ....................................... ..................................................... 7 3. Construction of THOR .................. ........................................................ 8 3-1 Overview .................................. ............................................. 8 3-2 Mechanical Parts ...................... ......................................... 11 3-3 Electrical Parts ......................... .......................................... 15 4. Basic Mechanics behind THOR ...... ................................................. 18 4-1 Movement ................................ .......................................... 18 4-2 Gripping and support ............... .......................................... 20 5. Working Principle of the Circuit ..... ................................................... 21 5-1 Connection Diagram ................ ............................................ 21 5-2 Sensing light ........................... ........................................... 23 5-3 Sensing heat ........................... ........................................... 24 6. Applications ................................... ..................................................... 25 7. Advantages .................................... .................................................... 26 8. Limitations ..................................... ..................................................... 28 9. Further Recommendation ............ .................................................... 29 10. Cost Analysis ............................. ................................................... 30 11. Conclusion ................................... ................................................... 31
References .......................................
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1. Introduction:
Since Karel Capek (1890-1938) first used the word ‘robot’, man has been infatuated with the creation of mechanized companions. Our project was named after the Norse god of thunder who used to banish evil to their demise. For it too might one day help humanity in its struggle against the evils of pollution and contamination. Our inspiration was the brave remote neutralization of a possible nuclear catastrophe by one of our hon’ teachers, Professor Dr. M.A. Taher Ali, when a jammed Co-60 source of the γ-beam irradiator at Bangladesh Institute of Nuclear Agriculture (BINA) threatened the lives of many in the late 80’s.
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2. Objectives: When THOR was still basically in the drawing board, we sketched up some goals we would like to achieve with our project in due course. Our main objectives were to :-
Manually maneuver into hazardous environment. Avoid obstacles and detours on the way using fast directional control. Grip mission objectives with link-driven gripper Bring objective back into safe containment area and deposit. Sense heightened level of temperature or lack of light on due process and indicate.
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3. Construction of THOR 3-1. Overview:
CAD simulation/schematics:
Fig 1: L.H.S View of THOR
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Fig 2. : Top View of THOR
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Fig 3: Overall Look
Real time view:
Fig 4: Real Time Top View
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Fig 5: THOR- in action
3-2. Mechanical Parts: Ball Bearing:
Ball bearings, as shown below, are probably the most common type of bearing. They are found in everything from inline skates to hard drives. These bearings can handle both radial and thrust loads, and are usually found in applications where the load is relatively small.
Photo courtesy The Timken Company
Fig 6: Cutaway view of a ball bearing
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In a ball bearing, the load is transmitted from the outer race to the ball and from the ball to the inner race. Since the ball is a sphere, it only contacts the inner and outer race at a very small point, which helps it spin very smoothly. But it also means that there is not very much contact area holding that load, so if the bearing is overloaded, the balls can deform or squish, ruining the bearing. In our project ball bearings were also used to allow relative motion between two moving/rotating members, namely the shaft and the housing that supported them longitudinally.
Acrylic parts: Acrylic is a useful, clear plastic that resembles glass, but has properties that make it superior to glass in many ways. Common brands of high-grade acrylic include Polycast, Lucite and Plexiglass.
Fig 7: Acrylic Sheets
A great advantage of acrylic is that it is only half as heavy as glass. This makes working with acrylic much easier. It can also be sawed, whereas glass must be scored.
13 Adding to this favorable array of properties, a transparency rate of 93% makes acrylic the clearest material known . This adds to the aesthetics of a project such as ours. A unique property of plastic is its ability to be shaped. Bow-front aquariums are beautiful examples of acrylic's wonderful properties. There are also no seams in acrylic structures, as chemical welding at the molecular level actually "melts" seams into one piece of solid material. Seams that are welded and polished are invisible. In our project acrylic was used to build: • Gripper Arm • Gripper Claw • Gripper Base • Upper floor of THOR.
Gear Motors: Gearmotors are a class of motors equipped with either an integral gear box or gear reduction unit. The set of gears drive a secondary drive shaft. These motors are capable of increasing the torque generating capacity of the motor while simultaneously reducing its output speed. A major advantage that comes with the usage of gears of this type is that the driving shaft is coupled directly to the driven shaft. Furthermore, they eliminate the necessity for coupling the motor to a separate external speed reducer. These motors are common in hot melt glue pumps, conveyor drives, tape dispensers, labeling, box tapers, case erectors and heat shrink tunnels.
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Fig 8: Cutway view of a Gear Motor
4 gear motors of variable RPM and torque were used to complete the structure of THOR and to support its various functions. Two motors with high operating torque were used to drive the two forward wheels. Equal RPM range was maintained to ensure uniformity of motion. Gear motors were selected for their various tangible advantages over other motors like the stepper motor. For example, gear motors had simpler working principle, required less effort to run seamlessly, had much better operating torque and were in general , a lot more durable.
Wooden components, springs and wires: After much deliberation, wood was included into material list. A base was built out of wood to support the weight of the power unit and the gripping tower above. Wood was also used to build the motor and shaft supports underneath the base. A spring was used in between the acrylic jaw to help keep them open after an ungripping operation.
15 Fig 9: Compressing spring and Nylon wires.
Compression springs were chosen to do this job because of their natural resistance to compression and durability. High strength nylon wires were used to drive and control the jaw and the gripper arm.
Mild Steel Driving Shaft: A drive shaft, driving shaft, propeller shaft, or Cardan shaft is mechanical device for transferring power from the engine or motor to the point where useful work is applied. Most engines or motors deliver power as torque through rotary motion: this is extracted from the linear motion of pistons in reciprocating engine; water driving a water wheel; or forced gas or water in a turbine. From the point of delivery, the components of power transmission form the drive train.
a
a
Fig 10: Gear and Shaft Coupling
Drive shafts are carriers of torque: they are subject to torsion and shear stress, which represents the difference between the input force and the load. They thus need to be strong enough to bear the stress, without imposing too great an additional inertia by virtue of the weight of the shaft. In our project, Mild steel was chosen as shaft material because of their ductile nature and availability.
3-3. Electrical Parts: The electrical semantics of THOR consisted of several simple circuit components (as shown below)
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Fig 11: Overall view of the circuit
LM-324 Operational Amplifier: An operational amplifier, which is often called an opamp, is a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation. High input impedance at the input terminals and low output impedance are important typical characteristics. Fig 12: Close-up of LM 324 Op-Amp
Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices
Light Dependent Resistor (LDR): A photoresistor or Light Dependent Resistor or CdS Cell is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor.
17 A photoresistor is made of a high resistance semiconductor. If light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron (and its hole partner) conduct electricity, thereby lowering resistance. Fig 13: Light Dependent Resistors.
NTC Type thermistor: A
thermistor is a type of resistor with resistance varying according to its temperature. In our case the thermistor in use was the “Negative Temperature Coefficient” or NTCtype thermistors. From geometric POV it was a “Bead Type Thermistor. NTC thermistors are used as resistance thermometers in low-temperature measurements of the order of 10 K.
Fig 14: NTC-type ‘BEAD’ thermistor.
Variable Resistances: Variable resistances have adjustable resistance which can be modified by changing the position of a tapping on the resistive element Variable resistances in the range of 10KΩ were used as a means of calibration between sensor outputs and indicators. Fig 15: Variable Resistance
Resistors: A resistor is a two-terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V = IR. The resistance R is equal to the voltage drop V across the resistor divided by the current I through the resistor. Resistors in the constant range of 10 KΩ, 1MΩ and 2MΩ were used in THOR’s sensor circuit. Fig 16: Resistor
LEDs: LED is a semiconductor diode that emits light when an electric current is applied in the forward direction of the device, as in the simple LED circuit. The effect is a form of electroluminescence where incoherent and narrowspectrum light is emitted from the p-n junction.
18 LEDs are widely used as indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. In THOR, two LEDs (one Green and one Red) were used to indicate lack of light or heightened temperature. Fig 17: LED and its working principle
DPDT Toggle Switches:
Double Pole Double Throw (DPDT) switches were used to control the motor directions i. These switches are useful in changing the polarity of the motor inputs on operation instantaneously. Fig 18: DPDT switch
4. Basic mechanics behind THOR
4-1. Movement:
19 On our quest for fast, multidirectional movements, we came across the idea of a PseudoHolonomic drive. On a fully Holonomic drive, the vehicle in question can instantaneously change direction of motion and progress. Non-holonomic robots are ones that cannot instantaneously move in any direction, such as a car. This type of robot has to perform a set of motions to change heading. For example, if you want your car to move sideways, you must perform a complex 'parallel parking' motion. For the car to turn, you must rotate the wheels and drive forward.
Non-Holonomic Movement
Holonomic Movement
Fig 19: Explanation of the difference between traditional and holonomic movements.
A holonomic robot however can instantaneously move in any direction. It does not need to do any complex motions to achieve a particular heading. This type of robot would have 2 degrees of freedom in that it can move in both the X and Y plane freely THOR’s movements weren’t completely Holonomic, thus the prefix “Pseudo”. Our project was granted the ability to turn instantaneously first and then move forward or backward. A feat otherwise considered unachievable in standard, Ackerman steering systems seen in everyday automobiles.
Strategy: To go forward or backward both wheel rotate in common direction
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Fig 20: ‘Forward Moving’ strategy
To steer/turn, wheels are rotated in opposite directions:
Left Turn
Right Turn
Fig 21: Steering Strategy
RW rotates opposite to LW to change direction and vice versa. Smooth turns are made possible by stopping one of the wheels and resuming the other
4-2. Gripping and support: Gripping commences when an object is placed between the jaws of the grip. Wires are pulled from the body of THOR via a gear motor and the jaw is closed thereby entrapping the object in question.
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Fig 22: Gripping Claw
When there is a need to ungrip, the wires are loosened by turning the motor in the opposite direction. The compression spring helps the claws return to their natural position.. All the time the custom designed, link-based “Gripper Arm” help keep the claw in a literally vertical position.
Fig 23: Gripper Arm
The arm is lowered or taken up via another gear motor attached to THOR’s exoskeleton. Again, wires are used to control the height of the arm.
5. Working principle of the circuit
22 A small, simplistic sensor circuit powers the senses of THOR. With its help, THOR can sense heightened level of temperature or a lack of light in the ambient environment. The basic principles in action here are: LDR senses lack of light and indicates with a Green LED. NTC-Type thermistor senses increase in temperature and indicates with a Red LED Possible to calibrate sensors according to ambient variables. In circuit “ Operational Amplifier ” ( LM-324 ) synchronizes between sensor feedbacks and indicators.
5-1. Connection diagrams
LM-324/124
Fig 24: Schematic of LM-324 (TOPView)
the
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Fig 25: Schematic of the Op-Amp connection
5-2. Sensing Light:
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Fig 26: Circuit diagram for the Sensing of Light
Under full incident light (spectral range of 515 nm ~ 730 nm) , LDR, with its decreased resistance, renders the path to the LED inactive. In darkness, its resistance increases. Op-Amp compares the feedback and lights up the green LED.
5-3. Sensing temperature:
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Fig 27: Circuit diagram for Sensing of heat.
Under increased temperature, the NTC type thermistor resistance is decreased rendering it inactive in the circuit. Op-Amp again compares the feedbacks and lights up the red LED. When ambient temperature recedes to normal, the resistance increases cutting off power supply to the LED.
6. Applications
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Fig 28: Possibly Applications- Minesweeping (Left) & Interstellar missions (Right)
THOR at its infancy is but only an engineering project. However with proper planning it maybe employed in a variety of useful purposes: Reconnoitering through possibly radioactive or hazardous environment. Salvage mission over terrains unsuitable for human exposure. Charting terrain as a drone for possible thermal leakage , heat flux and variation in luminescence Working as a multirole companion for humanitarian teams and missions. Small scale forklifting and payload carrying. Mapping favorable routes for friendly forces in wartime. With interchangeable arm-mounts, THOR has been given the ability perform a multitude of feats. For example, welding torches or surveillance cameras can be mounted in place of the claw to execute important repair or salvaging operations.
7. Advantages:
27 Our project has distinct characteristics which makes it advantageous for use under particular circumstances. For example:-
Our project was extremely cost effective. This is easily visible when logistical considerations are made. For example over the range of -50°C to 150°C, NTCtype thermistors offer a distinct advantage in sensitivity to temperature changes compared to other temperature sensors like Pt-RTD.
Fig 29: Resistance Vs Temp Graph
Another smart logistical consideration was the usage of LDR to sense light. Light Dependent Resistors (LDR) provides a comfortable range of resistive outputs to work with.
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Fig 30: Resistance Vs Light Intensity graph
However, when logistically considering, both the NTC-type thermistor and the LDR cost less than 0.3 USD. Certainly an economically viable consideration. Acrylic was used instead of wood. This made the whole project lightweight and easy to operate. Manual control was chosen over automated maneuvering. This helped ease the complexities of navigation make it more efficient. THOR was coupled with a high torque mechanism. So should the need for a heavier payload arises, our project would be able to support it on its back too. When there is a need to take sharp turns, THOR will be able to accomplish that using its “Pseudo-Holonomic” drive. Where there is a strong regulation against spilling, THOR would be able to operate because of its ingenious “Always Horizontal” gripping mechanism. THOR was given the ability to sense heat and light. This gives the project an edge over other similar initiatives. Because of its sensing omnipotence, THOR is more suitable for rover-missions.
8. Limitations No engineering project is without flaws. There are always places and instances where and when failure may occur. It would be ludicrous to assign 100% reliability on any material in
29 question. Likewise, our project too had limitations, limitations that restricted some of its operations, limitations that often caused failures at particularly weaker segments of its built. Some of these limitations were: Weak ‘Acrylic’ parts: Although lighter than more conventional materials like ‘wood’ Acrylic parts are vulnerable to sudden shock-loads. That is why there is often a concern of structural failure when THOR is test-driven. Connection Breakage: It was not possible to ensure a strong bondage between the wire contacts and the motor leads. The wiring of the motors and DPDT switches often breaks loose, rendering the motors ineffective and without power. Transducing difficulties: The bead type thermistor is not as well responsive as the LDR. So the signaling might be delayed. That is why the sensing of light is much well responsive that that of heat. Wire tension and severing: The wires used for gripper and arm-control is not that strong in tension and might sever under much heavier payloads.
9. Further recommendation
30 After the completion of any project, the question that first arises is “How to optimize the current configuration?” Our project too has many optimization and improvement opportunities. Such as:-
Replacing acrylic parts with stronger materials, like HDPE (High Density Poly Ethylene) or Aluminum. This would retain THOR’s lightweight built while increase strength/unit length , Integrating radio frequency control and servo drives. RF controlling would bring a new degree of freedom to THOR’s navigation relieving the operating hand of the concern of wire tangling. Incorporating solar-power for prolong operation. With a depletable power source like integrated DC batteries, THOR remains vulnerable to power shortage when operating times are increases. That is why photovoltaic cells empower by solar power maybe embedded later on to give THOR a whole new dimension. Automating directional commands via microcontrollers. Automation, although prone to system failures, is none the less a very efficient method to accomplish a pre-set sequence of objectives. So if the necessity arises for such an objective, THOR’s circuits can be coupled with a programmable microcontroller. Replacing LDR with more sensitive sensors such as phototransistors. This would increase THOR’s sensitivity to light and make it more responsive in crucial times.
10. Cost Analysis
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Item No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
Name Acrylic Base Acrylic Arm Gear Motor Solid rod of Mild steel Nuts & Bolts Bearing Spring & Washers Battery Bread Board DPDT switch Extension Wires IC(LM-324) LDR NTC type Thermistor LED Machining Cost Others Total
11. Conclusion
Quantity 2*(9 inch * 6 inch) 4 links + Claw 4 pieces 3 feet 150 pieces 10 pieces --------1 piece 1 piece 4 pieces 7 gauges 1 piece 1 piece 1 piece 2 pieces -------------
Price(Tk.) 320 300 1600 240 180 150 30 400 250 200 140 16 10 15 4 500 845 5200
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Throughout our sessional course we came across many difficulties. We entered as freshmen in the science of instrumentation and by the end of the semester we had transformed into much more potent engineers. We were able to successfully carry out all the objectives we initially set out to achieve. We learned much throughout the semester, about mechanical and electrical components and most importantly about human resource management. However, the finalé which included the joy of accomplishment would remain radiant in our memories for ever. All in all that was quite a delightful experience Finally, we would like to say that THOR has many scopes for improvement. We hope our juniors or any other interested reader would be able to improve and revitalize our project furthermore in the future. We would be highly delighted to help out anyone seeking general & technical help, information or suggestions regarding our project. Anyone interested about our project can reach us at the following website: http://project-thor.pbwiki.com
References
33 1. Report on salvage of a jammed cobalt-60 source of the gamma beam irradiator at Bangladesh Institute of Nuclear Agriculture (BINA), Mymensingh, Bangladesh - S M F Karim, K O Awal and M A T Ali http://www.iop.org/EJ/abstract/0952-4746/17/1/004 2. The International Journal of Robotics Research, Vol. 4, No. 1, 3-12 (1985) DOI: 10.1177/027836498500400101. Control and Geometrical Considerations for an Articulated Robot Hand - Hiroaki Kobayashi 3. “JOINT COUPLING DESIGN OF UNDERACTUATED GRIPPERS” - Aaron M. Dollar and Robert D. Howe. Proceedings of IDETC/CIE 2006 ASME 2006 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference September 10-13, 2006, Philadelphia, Pennsylvania, USA 4. Robot Mechanisms and Mechanical Devices Illustrated- Paul Sandin. Publisher: McGraw-Hill/TAB Electronics; 1 edition (June 27, 2003). ISBN-13: 9780071412001 5. Johnsson, M., & Balkenius, C. (2007). LUCS Haptic Hand III - An Anthropomorphic Robot Hand with Proprioception. LUCS Minor 13. 6. ASME “Magazine of Mechanical Engineering” Aug 2000 Issue http://www.memagazine.org/backissues/membersonly/aug00/features/fact/fact.html 7. Society of Robots http://www.societyofrobots.com/robot_omni_wheel.shtml 8. Digital Temperature Measurement http://www.educypedia.be/electronics/circuitssensortemp.htm 9. Mechatronics Wiki http://hades.mech.northwestern.edu/wiki/index.php? title=Main_Page 10. Negative Temperature Coefficient Thermistors http://www.designinfo.com/cornerstone/ref/negtemp.html