Stanford University · 2012. 10. 10. · The Mesicopter A Meso-Scale Flight Vehicle Stanford...
Transcript of Stanford University · 2012. 10. 10. · The Mesicopter A Meso-Scale Flight Vehicle Stanford...
The Mesicopter
A Meso-Scale Flight Vehicle
Stanford University
Prof. Ilan Kroo, Dept. of Aero/AstroProf. 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?◆ 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◆ Windshear, turbulence
monitors◆ Biological/chemical hazard
detection
■ Planetary Atmospherics◆ Swarms of low-mass mobile
robots for unique data onMars
■ Why rotorcraft for meso-scale flight?◆ 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-scaleflying devices possible.
The Concept: Rotorcraft
The Concept: Challenges
■ Insect-ScaleAerodynamics
■ 3D Micro-Manufacturing
■ Power / Control /Sensors
Challenges: Aerodynamics
■ Insect-scale aerodynamics◆ Highly viscous flow◆ All-laminar◆ Low L/D
■ New design tools required
Challenges: Micro-manufacturing
■ Efficient aero requires 3-D rotor design with 50µm cambered blades
■ Micro-motor design, construction
■ Integrated power, electronics
(a)
Equipment at Rapid Prototyping Lab
Approach
■ Advanced aerodynamic analysis anddesign methods
■ Novel manufacturing approaches
■ Teaming with industry for power andcontrol concepts
■ Stepwise approach using functionalscale model tests
Approach: (Super) Scale Model Development
■ Meso-scale prototypes:◆ 3g and 15g devices◆ Focus on rotor aero, power
■ Stability and control testbeds◆ 3 prototypes (60 – 100g)◆ Focus on stability and control◆ Near-term applications
Approach: Aerodynamics
■ Navier-Stokes analysis ofrotor sections atunprecedented lowReynolds number
■ Novel results of interest toMars airplane program
■ Nonlinear rotor analysisand optimization code
Aerodynamics: Airfoil Analysis
■ New results for very low Reairfoils
■ Very thin sections required
■ Maximum lift increases as Redecreases below 10,000
Aerodynamics: Airfoil Analysis
Aerodynamics: Airfoil Analysis
Aerodynamics: Section Optimization
■ Nonlinear optimization coupledwith Navier-Stokes simulation
■ New very low Re airfoil designs
■ Improved performance comparedwith previous designs
Aerodynamics: Section Flight Testing
■ Micro sailplanes permittesting of section properties
■ Difficulties with very lowforce measurements in windtunnel avoided
■ Optical tracking system
Aerodynamics: Rotor Optimization
■ Chord, twist, RPM, blade numberdesigned using nonlinear optimization
■ 3D analysis based on Navier-Stokessection data
■ Rotor matched with measured motorperformance
Approach: Rotor Manufacturing
1. Micro-machine bottomsurface of rotor on wax
2. Cast epoxy
3. Remove excessepoxy 4. Machine top
surface of rotor
5. Melt wax
Rotor Manufacturing: Materials and Methods
■ Wide range of rotor designsfabricated and tested
■ Scales from .75 cm to 20 cm
■ Materials include epoxy,polyurethanes, carbon
Rotor Manufacturing: Validation
■ Scanning electronmicroscopy to verify sectionshape
■ 3D laser scans to determineas-built camber, twist
■ Machining process revisedbased on initial results
Aerodynamics: Rotor Testing
■ Milligram balance■ Precision test stand■ Torque and force
measurements
Approach: Power and Control Systems
■ Energy storage
■ Motors
■ Sensors and Control
Power and Control Systems: Energy Storage
■ Power sources tested◆ COTS batteries (NiCd, NMH, AgZn,
Lithium, in many sizes)◆ Super-capacitors
■ SRI developing “direct-write” batteryunder DARPA program. High energydensity system integrated with small-scale 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
1
10
100
1000
0.1 1 10 100
We ig ht (g )
Spec
ific
Ener
gy (m
WH
/g)
Power and Control Systems: Motors
■ Small scale motors studied◆ Smoovy 3mm, 5mm◆ MicroMo 1.9mm
■ Larger, efficient DC motors◆ Westech series, Smoovy 8mm
■ Inexpensive prototype Mabuchi motors
■ Micro-motor development
Power and Control Systems: Motor Scaling
Small Mo to r Pe rfo rmanc e
0.010
0.100
1.000
10.000
0.01 0.1 1 10 100 1000
We ig ht (g )
Spec
ific
Pow
er W
/g
Power and Control Systems: Motor Control
■ Closed loop control ofbrushless DC motors:controller weight reduced
■ Speed control interfacedwith wirelesscommunication system
Power and Control Systems: Sensors / Control Laws
■ Innovative passivestabilization under test atlarger scale
■ Linear stability analysissuggests configurationfeatures
■ MEMS-based gyros providedamping
Approach: Prototypes
■ Initial 3g device with externalpower, controllers
■ Basic aero testing complete■ Issues: S&C, electronics
miniaturization, power
Approach: Prototypes
■ Capacitor powered mesicopter◆ 5mm Smoovy◆ Integrated electronics◆ Shrouded frame
Approach: Prototypes
■ Low cost unaugmented60g system
■ Includes receiver, speedcontrollers, lithiumbatteries
■ Tethered flights to date■ Sufficient lift for added
flight control electronics
Approach: Prototypes
■ PC-board system withdigital communicationand on-boardmicrocontroller
Approach: Prototypes
■ Larger 100g device■ WesTech coreless motors■ Significant payload capability
Approach: Prototypes
■ Mars rotor design and test
■ Rotor designed for Mars atmosphere
■ Fabricated using mold, carbon epoxy
■ Test at JPL in Mars environmentchamber
■ Results encouraging, but incomplete
Current Work
■ Continued rotor testing, optimization
■ Focus on stability and control issuesusing testbeds
■ Integration of electronics
■ Closed-loop autonomous flight
Future Work
■ Near-term applications◆ Mars rotorcraft◆ Testbed for multi-agent, cooperative control
■ Longer term aspects◆ Alternate power source potential◆ Further miniaturization of electronics◆ New sensor concepts