Aeromechanic Models for Flapping-Wing Robots With Passive Hinges in the Presence of Frontal Winds

Following the emergence of small flight-capable flapping-wing micro air vehicles, efforts toward autonomous outdoor operations of these small robots outside controlled laboratory conditions have been made. For the robots to overcome wind disturbances, it necessitates better insights into the interaction between the aerodynamics of flapping wings in the presence of winds and the robot's actuation system. In this paper, we consider the effects of constant frontal wind on a direct-drive flapping wing robot with passively rotating hinges and a compliant transmission. A simplified quasi-steady model that encapsulates the effects of frontal wind on aerodynamic forces is proposed. The model facilitates the calculation of periodic aerodynamic forces from nominal flapping kinematics. When combined with the dynamics of the actuation system, we are able to predict the lift force generated by the robot from the driving signals, without direct measurements of the flapping kinematics or the angle of attack. The proposed framework was experimentally verified on a flapping-wing robot prototype with a single wingspan of 76 mm. The results reveal up to 40% increases in lift when the robot was subject to 2.5 m/s horizontal winds. An analysis of the frequency response of the system is also provided to explain the resonance principles of the robot in the presence of frontal winds.