Miniature flapping flight systems hold great promise in matching the agility of their natural counterparts, bees, flies, and hummingbirds. Characterized by reciprocating wing motion, unsteady aerodynamics, and the ability to hover, insect-like flapping flight presents an interesting locomotion strategy capable of functioning at small size scales and is still a current focus of research. A vehicle with the capabilities of a fly would have potential use as miniature nodes in sensor networks, near invisible surveillance platforms, and mobile vehicles in search and rescue. Designing and constructing such systems, however, is difficult. Beyond the limits of battery capacity and the difficulties of miniature sensor design, simply producing enough lift for liftoff is a challenge. A balance must be maintained between mechanical complexity, controllability, and weight. While more actuators generally lead to more controllable degrees of freedom, they also contribute significantly to system mass.
In light of these constraints, we choose to utilize passive behavior and mechanical resonance when possible. We develop platforms utilizing passive wing rotation, where the wing leading edge is driven and the trailing edge is allowed to rotate based on elastic energy storage, wing aerodynamics, and inertial effects. Wing flapping motion is allowed to resonate through the choice of cantilever actuator or added elastic element. Systems are constructed at two different size scales, using piezoelectric actuators and motors to drive the wing leading edge.
In this work the design of several controllable flapping flight micro aerial vehicles is discussed and platform underactuation, control development, and active and passive stability is examined. At under one gram, both a 700 mg and 160 mg system are constructed with a single piezoelectric actuator driving each wing. Design considerations including structure rigidity, controllability and mass centralization are considered, with body finite element analysis and wing coupling tests performed. The constructed 160 mg prototype is shown to achieve a lift-to-weight ratio of ~3/8. With an actuator driving each wing, the system is capable of producing altitude controlling forces as well as pitch and roll torques with a change in wing flapping amplitude. An alternative means of generating wing asymmetry for lift control is proposed and implemented with a shape memory based flexural hinge. Lift control is demonstrated on a modified flapping platform with an application of heat. At a larger 3 and 7 grams, a two and four wing motor-driven flapping platform is designed and constructed. With the use of an elastic element in parallel with the flapping motion, the motor driven design is able to resonate, resulting in a novel and simple lift-off capable system. Motor, flapping frequency, and wing size are chosen based on impedance matching criteria, and further experimentally optimized. Control of both piezo and motor-driven platforms is demonstrated in both simulation and in limited control experiments with a developed robust and linear controller respectively.
Metin Sitti (Chair)
Xinyan Deng (Purdue University)