Design and control of a hummingbird-size flapping wing micro aerial vehicle

Jian Zhang, Purdue University

Abstract

Flying animals with flapping wings may best exemplify the astonishing ability of natural selection on design optimization. They evince extraordinary prowess to control their flight, while demonstrating rich repertoire of agile maneuvers. They remain surprisingly stable during hover and can make sharp turns in a split second. Characterized by high-frequency flapping wing motion, unsteady aerodynamics, and the ability to hover and perform fast maneuvers, insect-like flapping flight presents an extraordinary aerial locomotion strategy perfected at small size scales. Flapping Wing Micro Aerial Vehicles (FWMAVs) hold great promise in bridging the performance gap between engineered flying vehicles and their natural counterparts. They are perfect candidates for potential applications such as fast response robots in search and rescue, environmental friendly agents in precision agriculture, surveillance and intelligence gathering MAVs, and miniature nodes in sensor networks. Designing and developing such systems is a challenging problem under stringent constraints in size, weight and power (SWaP). In addition, the lagging in battery technology, requirement on miniature sensors and actuators for navigation, limited on-board computational power, and system integration all pose challenges in design. Under the SWaP constraints, balance and trade-off must be made among mechanical complexity, controllability, power, and weight. Otherwise, even producing enough lift to sustain the weight can be a challenge. In this thesis, we present a systematic approach of vehicle design and optimization, resonance design, and flight control. Achieving resonance in flapping wings has been recognized as one of the most important principles to enhance power efficiency, lift generation, and flight control performance of high-frequency FWMAVs. Most of the work on the development of such vehicles have attempted to achieve wing flapping resonance. However, theoretical understanding of its effects on the response and energetics of flapping motion has lagged behind, leading to sub-optimal design decisions and misinterpretations of experimental results. In this thesis, we systematically model the dynamics of flapping wing as a forced nonlinear resonant system, using both nonlinear perturbation method and linear approximation approach. We derived analytic solution for steady-state flapping amplitude, energetics, and characteristic frequencies including natural frequency, damped natural frequency, and peak frequency. Validated with both simulation and experiments, our results showed that both aerodynamic lift and power efficiency are maximized by driving the wing at natural frequency, instead of other frequencies. Interestingly, the flapping velocity is maximized at natural frequency as well, which can lead to an easy experimental approach to identify natural frequency and follow the resonance design principle. The result can serve as a systematic design principle and guidance in the interpretations of empirical results. For the vehicle design and prototype of FWMAV, we presented a complete, multidisciplinary formulation for system design optimization and integration for a Hummingbird-size FWMAV. The formulation covers actuation, wing, battery, electronics, dynamics, flight stability and control. System parameters considered include parameters of wings, motors, gears, springs, batteries, control authorities, and locations of poles and zeros of the system dynamics. The formulation was validated by experimental data for both rigid and flexible wings, covering low to high wing loading. Based on the direct motor drive mechanism of this work, the optimization yields a prototype with on-board sensors, electronics, and computation. It has a wingbeat frequency of 30Hz to 40Hz, with 12 grams of total weight and 20 grams of maximum lift. Liftoff was demonstrated with extra payloads. Initial results of on-board state estimation and flight control were performed. Flapping wing platforms with different requirements and scales can now be systematically designed and optimized with parameter modifications of the proposed formulation. Not only do we have to design and develop the system under the SWaP constraints, we also need to control the system under those tight constraints as well. The superior maneuverability of insect flight is enabled by rapid and significant changes in aerodynamic forces, a result of subtle and precise changes of wing kinematics. The high sensitivity of aerodynamic force to wing kinematic change demands precise and instantaneous feedback control of the wing motion trajectory, especially in the presence of various parameter uncertainties and environmental disturbances. Current work on flapping wing robots was limited to open-loop averaged wing kinematics control. Here we present instantaneous closed-loop wing trajectory tracking of a DC motor direct driven wing-thorax system under resonant flapping. Finally, we present an analysis on fundamental limitations of flapping flight control and discovered, for the first time, the non-minimum phase nature of flapping flight when certain controls are used. We then presented full nonlinear attitude and position controller with exponentially stable and globally exponential attractive properties. The dynamics and flight control results were then illustrated by experimental results.

Degree

Ph.D.

Advisors

Deng, Purdue University.

Subject Area

Mechanical engineering|Robotics

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