Investigation on force transmission of direct-drive thorax unit with four ultrasonic motors for a flapping microaerial vehicle

We fabricated a trial version of a thorax unit with four ultrasonic motors (USMs) to simulate a dragonfly-scale flapping micro aerial vehicle (MAV). Each wing was directly driven by a two-degree-of-freedom (2-DOF) transmission. An in-house tiny standing-wave USM capable of bidirectional rotation, which weighs just 0.13 g, was employed on trial. The transmission of the thorax unit converts the two USM rotations into strokes and flip motions of the wing. By implementing two 70-mm-long wings, we fabricated a prototype of a 4-DOF MAV and tested its performance. In a lift-compensated situation, upward, forward, and backward movements of the MAV were obtained. The flapping angular velocity was discussed based on quasi-static wing aerodynamics and was accountable for the motor power. Although the power of the USM should be improved, the quick wing drivability, adequate power transmission on the thorax unit, and potential of a 0.2 W motor power in a unidirectional-type USM promise the viability of a direct-drive multi-DOF dragonfly-scale MAV.