Thorax unit driven by unidirectional USM for under 10-gram flapping MAV platform

A unidirectional ultrasonic motor (USM) is applied to the thorax unit of a flapping micro aerial vehicle (MAV) with the aim to develop an MAV in the 10-gram-range, for which appropriate DC motors with high power-weight ratios are unavailable. As a trial, a unidirectional USM having an ultrasonic transducer with mass of 336 mg and rotor of 3 mm diameter is implemented to a belt drive mechanism in place of a DC motor and spar gear unit. At no load and without wings, the USM works well and achieves a flapping frequency exceeding 32 Hz, while the output power is around 36 mW owing to the mismatch of the two vibration modes that dominate the efficiency of the USM. Although the observed lift force remains low because of the lack of USM power and heaviness of the wings, the appropriateness of the mechanical design is confirmed and improvements toward the 10-gram-range flapping MAV with USM are discussed on the basis of these results. Another actuation mechanism of the flapping MAV is proposed.