An untethered sub-gram flapping-wing flight system achieves sustained self-stabilizing and altitude-controlled flight

Insect-scale flapping-wing micro aerial vehicles offer substantial potential for applications such as search and rescue. However, stringent power and payload constraints at the sub-gram scale have precluded sustained untethered flight. Inspired by the high lift generated by full-circumferential rotor motion, this study presents a cross-shaped piezoelectric direct-drive V-wing structure. The structure uses a tuning-fork vibration mode to generate full-circumferential flapping, suppressing fuselage vibration without external anchoring and substantially improving the lift performance of the piezoelectric direct-drive flapping-wing micro aerial vehicle. Based on this principle, we developed a cross-shaped four-piezoelectric-actuator V-wing micro aerial vehicle weighing 389 mg with a wingspan of 6.8 cm, capable of generating a maximum lift of 1850 mg. Waveform modulation increases the efficiency of the 173 mg drive circuit to 45%, while mechanical self-stabilization suppresses attitude disturbances. Integrated with a 350 mg battery, the 984 mg system achieves untethered, sustained, stable flight for a sub-gram flapping-wing micro aerial vehicle. The maximum lift-to-weight ratio of the untethered flapping-wing micro aerial vehicle system is 1.88. Its maximum flight altitude exceeds 10 m, and its continuous flight duration under low-power operation exceeds 240 s. The system also demonstrates altitude-controlled and disturbance-resilient untethered flight.