The Use of Resonance for Miniaturizing Flapping MAVs

Caspar Bolsman Björn Pållson, Hans Goosen, Rob Munnig-Schmidt and Fred van Keulen Toulouse September 18th, 2007

Structural Optimization & Computational Mechanics

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Contents • Introduction • Insects • Resonating structures

• Prototypes and experiments • Control • Conclusions

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Contents

Structural Optimization & Computational Mechanics

First aim • FMAV with 10 cm wingspan and 4 gram vehicle mass • Capable of hovering flight • To be used in an indoor environment

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Introduction

Structural Optimization & Computational Mechanics

This project • Development of a wing actuation mechanism  Interfaces with aerodynamics and mechatronics • Subjects:  Biologically inspired resonators  Actuator technology  Mechanism topology  Wing kinematics  Aerodynamic forces  Mechanisms for control 4

Introduction

Structural Optimization & Computational Mechanics

Overview • Current FMAVs  Traditionally gears and links are used  Actuation by electric motors  Great at larger scales • Drawbacks:  Scaling of gears and links  Complexity of mechanism  Friction

Photo Jean-Patrick Donzey

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Introduction

Structural Optimization & Computational Mechanics

Compliant mechanisms • Advantages  No need for gears  Possibility to scale down  Possibility to exploit resonance  Inspiration from insects • Drawbacks  Reduced freedom in wing kinematics  Linear actuator needed  Less design experience 6

Introduction

Structural Optimization & Computational Mechanics

Insects • Insect research needed for small scale flapping MAVs  Aerodynamics  Mechanics • Both are needed for realizing small scale hovering flight • Bio-inspired direct copying

Picture by Christopher Adlam

Picture by André Karwath

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Insects

Structural Optimization & Computational Mechanics

Insect flight • Three aerodynamic mechanisms  Leading edge vortex  Rotational circulation  Wake capture • Aerodynamics dictated by the wing kinematics • CFD too “expensive” for design setting • Quasi steady aerodynamic model used for calculations

Picture from F. Bos 2005

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Insects

Structural Optimization & Computational Mechanics

Insect mechanics • The insect thorax consist of:  Muscles  Thoracic structures and ligaments  Wing root joint • Well described at biological level  Two main muscles groups  Up to 14 control muscles  Reconfiguration of joint for each stroke 9

Insects

Structural Optimization & Computational Mechanics

FMAV thorax • • • • • •

Exploit resonance for more efficiency Tuned thorax wing system High Q factor for efficiency (>50) low Q for control (~2-3) Ratio inertial cost/aerodynamic dissipation Actuation near undamped natural frequency

M  K  f (t )  f ( , , t )

Resonating structures

Structural Optimization & Computational Mechanics

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FMAV thorax • Alternatives needed for:  Energy storage  Wing root mechanism • Complex joint not attractive • Energy storage can be done in many ways

Actuator

Thorax wing

Resonating structures

Structural Optimization & Computational Mechanics

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FMAV thorax • Coupling of the actuator can be done in many ways  Stiff or weak

Resonating structures

Structural Optimization & Computational Mechanics

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FMAV thorax • Approach here is starting from energy storage • Use of ring type structure  Needs no support structures for vibration  Can be coupled to the wings in many ways  Fully compliant Resonating structures

Structural Optimization & Computational Mechanics

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Prototypes • Ring type structure using weak coupling to the wings

Prototypes and experiments

Structural Optimization & Computational Mechanics

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Prototypes • Change to more stiff wing coupling • Two as well as four winged concepts

Prototypes and experiments

Structural Optimization & Computational Mechanics

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Experiments • Research on wing kinematics • Passive wing rotation

Prototypes and experiments

Structural Optimization & Computational Mechanics

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Control using Resonance • • • •

Flapping in horizontal plane Control around steady state hovering Large degree of pendulum stability assumed Different mechanisms for influencing the wings  Change of flapping amplitude  Change of centre position  Many others used by insects

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Control

Structural Optimization & Computational Mechanics

Change of flapping amplitude

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Control

Structural Optimization & Computational Mechanics

Challenges • Scaling laws S3 (power density) S2 (aerodynamic losses) • Linear actuators exhibit frequency dependant power output • Compliant structures require other design methodology • Control using resonating structures is less direct

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Challenges

Structural Optimization & Computational Mechanics

Conclusions • Insect inspired compliant mechanisms are very promising • Copying insects aerodynamics is possible • Control of resonating structures without active wing rotation seems feasible • By using compliant mechanisms downscaling is possible

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Conclusions

Structural Optimization & Computational Mechanics

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Structural Optimization & Computational Mechanics