Yaw Torque Authority for a Flapping-Wing Micro-Aerial Vehicle

Abstract

Flapping-wing micro-aerial vehicles rely on subtle changes in the kinematics of high-frequency wing flapping to produce roll, pitch, and yaw torques. To generate yaw torque, the Harvard RoboBee changes the ratio of upstroke to downstroke speed (“split-cycling”) by applying a second harmonic to the fundamental flapping signal for each wing. However, since flapping typically occurs near resonance (for efficiency), these higher harmonics are filtered out by the transmission and actuator dynamics. Therefore, reliable yaw control authority has proven elusive. We propose a method to generate yaw torque sufficient for in-flight control by using split-cycle flapping in an “iso-lift” regime, to mitigate resonant filtering by decreasing the flapping frequency and increasing the drive voltage, which produces lift identical to typical flight conditions. We model the expected torque at iso-lift conditions and apply this method to the physical RoboBee, achieving reliable, controllable yaw torque. Finally, we demonstrate yaw control with a simple heading controller, achieving a step response with a time constant an order of magnitude faster than previous attempts.