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