Anomalous yaw torque generation from passively pitching wings

Abstract

Small, lightweight micro-aerial vehicles (MAVs) must rely on a limited number of actuators for flight stability and control. A method for six-degree of freedom control in a dual-actuator MAV has been previously proposed which employs stroke amplitude, bias, and split-cycle timing modulation. This control scheme is the basis of actuation for stable, controlled flapping wing flight of the Harvard Robobee. The role of passive wing pitching dynamics are currently unexplored in their effects on yaw-dynamics during free flight. Here we demonstrate in simulation and experiment the critical role wing pitching dynamics play in yaw control of a dual-actuated MAV using the split-cycle control scheme. We find that yaw-authority sensitively depends on the functional form of the wing hinge joint and that pitching dynamics of wing hinges with linear stiffness may compromise yaw control. To solve this we present a design method for laminate based non-linear hinges and demonstrate that non-linear hinge stiffness improves yaw torque generation during split-cycle actuation.