1. 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

2. 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

3. The Concept: Applications
Atmospheric Studies
Windshear, turbulence
monitors
Biological/chemical hazard
detection
Planetary Atmospherics
Swarms of low-mass mobile
robots for unique data on
Mars

4. The Concept: Rotorcraft
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-scale
flying devices possible.

5. The Concept: Challenges
Insect-Scale
Aerodynamics
3D Micro-
Manufacturing
Power / Control /
Sensors

6. Challenges: Aerodynamics
Insect-scale aerodynamics
Highly viscous flow
All-laminar
Low L/D
New design tools required

7. Challenges: Micro-manufacturing
Efficient aero requires 3-D rotor design with 50
μm cambered blades
Micro-motor design, construction
Integrated power, electronics
(a)
Equipment at Rapid Prototyping Lab

8. Approach
Advanced aerodynamic analysis and
design methods
Novel manufacturing approaches
Teaming with industry for power and
control concepts
Stepwise approach using functional
scale model tests

9. 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

10. Approach: Aerodynamics
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

11. Aerodynamics: Airfoil Analysis
New results for very low Re
airfoils
Very thin sections required
Maximum lift increases as Re
decreases below 10,000

12. Aerodynamics: Airfoil Analysis

13. Aerodynamics: Airfoil Analysis

14. Aerodynamics: Section Optimization
Nonlinear optimization coupled
with Navier-Stokes simulation
New very low Re airfoil designs
Improved performance compared
with previous designs

15. Aerodynamics: Section Flight Testing
Micro sailplanes permit
testing of section properties
Difficulties with very low
force measurements in wind
tunnel avoided
Optical tracking system

16. Aerodynamics: Rotor Optimization
Chord, twist, RPM, blade number
designed using nonlinear optimization
3D analysis based on Navier-Stokes
section data
Rotor matched with measured motor
performance

17. Approach: Rotor Manufacturing
1. Micro-machine bottom
surface of rotor on wax
2. Cast epoxy
3. Remove excess
epoxy 4. Machine top
surface of rotor
5. Melt wax

18. Rotor Manufacturing: Materials and Methods
Wide range of rotor designs
fabricated and tested
Scales from .75 cm to 20 cm
Materials include epoxy,
polyurethanes, carbon

19. Rotor Manufacturing: Validation
Scanning electron
microscopy to verify section
shape
3D laser scans to determine
as-built camber, twist
Machining process revised
based on initial results

20. Aerodynamics: Rotor Testing
Milligram balance
Precision test stand
Torque and force
measurements

21. Approach: Power and Control Systems
Energy storage
Motors
Sensors and Control

22. Power and Control Systems: Energy Storage
Power sources tested
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 small-scale
structure. Still under development.
Future technologies may include LiSO4,
micro fuel cells, micro-turbines.

23. Power and Control Systems: Battery Scaling
Batte ry Pe rfo rmanc e
1000
100
10
1
0.1 1 10 100
We ig ht (g )
Specific Energy (mWH/g)

24. 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

25. Power and Control Systems: Motor Scaling
Small Mo to r Pe rfo rmanc e
10.000
1.000
0.100
0.010
0.01 0.1 1 10 100 1000
We ig ht (g )
Specific Power W/g

26. Power and Control Systems: Motor Control
Closed loop control of
brushless DC motors:
controller weight reduced
Speed control interfaced
with wireless
communication system

27. Power and Control Systems:
Sensors / Control Laws
Innovative passive
stabilization under test at
larger scale
Linear stability analysis
suggests configuration
features
MEMS-based gyros provide
damping

28. Approach: Prototypes
Initial 3g device with external
power, controllers
Basic aero testing complete
Issues: SC, electronics
miniaturization, power

29. Approach: Prototypes
Capacitor powered mesicopter
5mm Smoovy
Integrated electronics
Shrouded frame

30. Approach: Prototypes
Low cost unaugmented
60g system
Includes receiver, speed
controllers, lithium
batteries
Tethered flights to date
Sufficient lift for added
flight control electronics

31. Approach: Prototypes
PC-board system with
digital communication
and on-board
microcontroller

32. Approach: Prototypes
Larger 100g device
WesTech coreless motors
Significant payload capability

33. Approach: Prototypes
Mars rotor design and test
Rotor designed for Mars atmosphere
Fabricated using mold, carbon epoxy
Test at JPL in Mars environment
chamber
Results encouraging, but incomplete

34. Current Work
Continued rotor testing, optimization
Focus on stability and control issues
using testbeds
Integration of electronics
Closed-loop autonomous flight

35. 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