Mechanics. • Both are needed for realizing small scale hovering flight. • Bio-inspired direct copying. Picture by André Karwath. Picture by Christopher Adlam ...
• 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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