The Mesicopter A Meso-Scale Flight Vehicle Stanford University Prof. Ilan Kroo, Dept. of Aero/Astro Prof. Fritz Prinz, Dept. of Mech. Eng.
Graduate Students: Peter Kunz, Gary Fay, Shelly Cheng, Tibor Fabian, Chad Partridge
The Concept: Meso-scale Flight ■
What is a meso-scale vehicle? ◆ ◆ ◆ ◆
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Larger than microscopic, smaller than conventional devices Mesicopter is a cm-scale rotorcraft Exploits favorable scaling Unique applications with many low cost devices
Objectives ◆ ◆ ◆
Is such a vehicle possible? Develop design, fabrication methods Improve understanding of flight at this scale
The Concept: Applications ■
Atmospheric Studies ◆ ◆
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Windshear, turbulence monitors Biological/chemical hazard detection
Planetary Atmospherics ◆
Swarms of low-mass mobile robots for unique data on Mars
The Concept: Rotorcraft ■
Why rotorcraft for meso-scale flight? ◆
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As Reynolds number and lift/drag decrease, direct lift becomes more efficient Compact form factor, station-keeping options Direct 4-axis control
Scaling laws (and nature) suggest cm-scale flying devices possible.
The Concept: Challenges
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Insect-Scale Aerodynamics 3D MicroManufacturing Power / Control / Sensors
Challenges: Aerodynamics
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Insect-scale aerodynamics ◆ Highly viscous flow ◆ All-laminar ◆ Low L/D New design tools required
Challenges: Micro-manufacturing (a)
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Efficient aero requires 3-D rotor design with 50 µm cambered blades
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Micro-motor design, construction
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Integrated power, electronics
Equipment at Rapid Prototyping Lab
Approach
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Advanced aerodynamic analysis and design methods Novel manufacturing approaches Teaming with industry for power and control concepts Stepwise approach using functional scale model tests
Approach: (Super) Scale Model Development
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Meso-scale prototypes: ◆ ◆
3g and 15g devices Focus on rotor aero, power
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Stability and control testbeds ◆ ◆ ◆
3 prototypes (60 – 100g) Focus on stability and control Near-term applications
Approach: Aerodynamics ■
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Navier-Stokes analysis of rotor sections at unprecedented low Reynolds number Novel results of interest to Mars airplane program Nonlinear rotor analysis and optimization code
Aerodynamics: Airfoil Analysis
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New results for very low Re airfoils Very thin sections required Maximum lift increases as Re decreases below 10,000
Aerodynamics: Airfoil Analysis
Aerodynamics: Airfoil Analysis
Aerodynamics: Section Optimization
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Nonlinear optimization coupled with Navier-Stokes simulation New very low Re airfoil designs Improved performance compared with previous designs
Aerodynamics: Section Flight Testing
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Micro sailplanes permit testing of section properties Difficulties with very low force measurements in wind tunnel avoided Optical tracking system
Aerodynamics: Rotor Optimization ■
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Chord, twist, RPM, blade number designed using nonlinear optimization 3D analysis based on Navier-Stokes section data Rotor matched with measured motor performance
Approach: Rotor Manufacturing
1. Micro-machine bottom surface of rotor on wax
3. Remove excess epoxy
2. Cast epoxy
4. Machine top surface of rotor
5. Melt wax
Rotor Manufacturing: Materials and Methods
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Wide range of rotor designs fabricated and tested Scales from .75 cm to 20 cm Materials include epoxy, polyurethanes, carbon
Rotor Manufacturing: Validation ■
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Scanning electron microscopy to verify section shape 3D laser scans to determine as-built camber, twist Machining process revised based on initial results
Aerodynamics: Rotor Testing ■ ■ ■
Milligram balance Precision test stand Torque and force measurements
Approach: Power and Control Systems ■
Energy storage
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Motors
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Sensors and Control
Power and Control Systems: Energy Storage ■
Power sources tested ◆ ◆
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COTS batteries (NiCd, NMH, AgZn, Lithium, in many sizes) Super-capacitors
SRI developing “direct-write” battery under DARPA program. High energy density system integrated with smallscale structure. Still under development. Future technologies may include LiSO4, micro fuel cells, micro-turbines.
Power and Control Systems: Battery Scaling Batte ry Pe rfo rmanc e
Spe c ific Ene rg y (mWH/g )
1000
100
10
1 0.1
1
10 We ig ht (g )
100
Power and Control Systems: Motors
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Small scale motors studied ◆ ◆
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Smoovy 3mm, 5mm MicroMo 1.9mm
Larger, efficient DC motors ◆
Westech series, Smoovy 8mm
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Inexpensive prototype Mabuchi motors
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Micro-motor development
Power and Control Systems: Motor Scaling Small Mo to r Pe rfo rmanc e
Specific Po wer W/g
10.000
1.000
0.100
0.010 0.01
0.1
1
10 We ig ht (g )
100
1000
Power and Control Systems: Motor Control
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Closed loop control of brushless DC motors: controller weight reduced Speed control interfaced with wireless communication system
Power and Control Systems: Sensors / Control Laws
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Innovative passive stabilization under test at larger scale Linear stability analysis suggests configuration features MEMS-based gyros provide damping
Approach: Prototypes ■
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Initial 3g device with external power, controllers Basic aero testing complete Issues: S&C, electronics miniaturization, power
Approach: Prototypes ■
Capacitor powered mesicopter ◆ ◆ ◆
5mm Smoovy Integrated electronics Shrouded frame
Approach: Prototypes
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Low cost unaugmented 60g system Includes receiver, speed controllers, lithium batteries Tethered flights to date Sufficient lift for added flight control electronics
Approach: Prototypes â–
PC-board system with digital communication and on-board microcontroller
Approach: Prototypes ■ ■ ■
Larger 100g device WesTech coreless motors Significant payload capability
Approach: Prototypes ■
Mars rotor design and test
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Rotor designed for Mars atmosphere
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Fabricated using mold, carbon epoxy
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Test at JPL in Mars environment chamber Results encouraging, but incomplete
Current Work ■
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Continued rotor testing, optimization Focus on stability and control issues using testbeds
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Integration of electronics
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Closed-loop autonomous flight
Future Work ■
Near-term applications ◆ ◆
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Mars rotorcraft Testbed for multi-agent, cooperative control
Longer term aspects ◆ ◆ ◆
Alternate power source potential Further miniaturization of electronics New sensor concepts