Analysis of a Tunable Impedance Method for Practical Control of Insect-Inspired Flapping-Wing MAVs

In the past decade, research into insect-inspired flapping-wing micro-aerial vehicles (FWMAV) has grown steadily, toward addressing unique challenges in morphological construction, force production, and control strategy. Remarkable results have emerged from work focused on generation of adequate lift force for levitation and vertical acceleration [1]; however, effective methods for motion control still remain an open problem. In this paper, we introduce and analyze a novel approach to FWMAV control problem that provides smooth, stable and independent flight in both vertical and horizontal maneuvers. Our insect-inspired MAV model employs a passive structure to adjust the angle of attack (AoA) of its wings. Further analysis of this design unveils its capability in creating significant amounts of net drag force without disturbing lift production. This is the foundation of 'tunable impedance' technique that allows us to independently control three basic motions. One controller regulates yaw and forward acceleration, utilizing intuitive PM control laws in order to control horizontal maneuvers. Lift force and corresponding vertical elevation changes are controlled by a second controller that modifies the frequency of a constant-amplitude, sinusoidal power stroke. A third controller stabilizes the vehicle's body pitch angle through biasing stroke angle of its wings, hence rejecting disturbances caused by fluctuations in the position of center of mass (CoM). Results of simulated experiments confirm that these three controllers together demonstrate exceptional ability in handling hovering or agile flight maneuvers - even in presence of moderate measurement noise. These results also suggest that employment of passive dynamics in the design of MAVs may not only reduce actuator bandwidth requirements - thus simplifying practical implementation of the vehicle - but also improve robustness to uncertainties in sensing and body morphology.