A robophysical investigation of series-elastic flapping wings
Flying insects may achieve energy efficient flight by storing and releasing elastic energy in their thorax, tendons, and muscle. Similarly, flapping wing micro-aerial vehicles (FWMAVs) may benefit from the inclusion of elastic components in their actuation system. Despite significant investigation into the aerodynamics of flapping wings, the actuation of these movements through elastic structures in insects and robots is relatively unexplored. We have developed a dynamically-scaled robophysical experiment to study the dynamics of series-elastic flapping wings, with specific emphasis on discovering the role of linear and nonlinear elastic components in energy efficiency, perturbation resistance, and control. We vary system (inertia and elasticity) and actuation (amplitude and frequency) parameters and find that energy storage and recovery by an elastic element is dependent on the stiffness of the element, the inertia of the system, and upon the driving amplitude and frequency. Experimental results are compared to the results of an analysis of a simplified model of the system. The comparison suggests that an effective model of elastic flapping wings must account for unsteady aerodynamic mechanisms that arise from the flow about the oscillating wing. The same experiments suggest that the inclusion of series-elastic elements may have a negative overall effect on control capabilities. The results of the project will inform the design of future FWMAVs, providing insight in elastic element selection, power requirements, and control design as well as addressing open questions in biology about actuation and control in flying insects.