Me So Scale Flight Vehicle

8/11/2019 Me So Scale Flight Vehicle

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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


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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


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The Concept: Applications

Atmospheric Studies

Windshear, turbulencemonitors

Biological/chemical hazard

detection

Planetary Atmospherics

Swarms of low-mass mobile

robots for unique data on

Mars


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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.

The Concept: Rotorcraft


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The Concept: Challenges

Insect-ScaleAerodynamics

3D Micro-Manufacturing

Power / Control /Sensors


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Challenges: Aerodynamics

Insect-scale aerodynamics

Highly viscous flow

All-laminar

Low L/D

New design tools required


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Challenges: Micro-manufacturing

Efficient aero requires 3-D rotor design with 50m cambered blades

Micro-motor design, construction

Integrated power, electronics

(a)

Equipment at Rapid Prototyping Lab


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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


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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


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Approach: Aerodynamics

Navier-Stokes analysis of

rotor sections atunprecedented low

Reynolds number

Novel results of interest to

Mars airplane program

Nonlinear rotor analysis

and optimization code


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Aerodynamics: Airfoil Analysis

New results for very low Reairfoils

Very thin sections required

Maximum lift increases as Re

decreases below 10,000


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Aerodynamics: Section Optimization

Nonlinear optimization coupledwith Navier-Stokes simulation

New very low Re airfoil designs

Improved performance compared

with previous designs


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Aerodynamics: Section Flight Testing

Micro sailplanes permittesting of section properties

Difficulties with very lowforce measurements in wind

tunnel avoided

Optical tracking system


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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


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Approach: Rotor Manufacturing

1. Micro-machine bottom

surface of rotor on wax

2. Cast epoxy

3. Remove excess

epoxy 4. Machine topsurface of rotor

5. Melt wax


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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


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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


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Aerodynamics: Rotor Testing

Milligram balance

Precision test stand

Torque and force

measurements


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Approach: Power and Control Systems

Energy storage

Motors

Sensors and Control


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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 energy

density system integrated with small-

scale structure. Still under development.

Future technologies may include LiSO4,

micro fuel cells, micro-turbines.


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Power and Control Systems: Battery Scaling

Batte ry Pe rformanc e

1

10

10 0

1000

0.1 1 10 100

We ight (g)

SpecificEnergy

(mWH/g)


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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


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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


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Approach: Prototypes

Initial 3g device with external

power, controllers

Basic aero testing complete Issues: S&C, electronics

miniaturization, power


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Capacitor powered mesicopter

5mm Smoovy Integrated electronics

Shrouded frame


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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


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PC-board system with

digital communication

and on-boardmicrocontroller


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Larger 100g device

WesTech coreless motors

Significant payload capability


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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


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Current Work

Continued rotor testing, optimization

Focus on stability and control issues

using testbeds

Integration of electronics

Closed-loop autonomous flight


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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

Me So Scale Flight Vehicle

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