Insect-inspired, tailless, hover-capable flapping-wing robots: Recent progress, challenges, and future directions

Flying insects are able to hover and perform agile maneuvers by relying on their flapping wings to produce control forces, as well as flight forces, due to the absence of tail control surfaces. Insects have therefore become a source of inspiration for the development of tailless, hover-capable flapping-wing air vehicles (FWAVs). However, the technical difficulty involved in designing and building such a complicated and compact system within a limited takeoff weight for it to remain airborne is a major barrier. Consequently, among the many developed vehicles, only a few are capable of free flight. In this review paper, we survey recent developments of insect-inspired tailless FWAVs in various sizes from micro-to pico-scale, with different types of driving actuator, mechanism design, wing configuration, and control strategy. We discuss the capability of free flight and flight endurance of the FWAVs, which are limited by current electronics and power technologies that severely constrain those vehicles using other driving actuators, rather than conventional electromagnetic motors, to freely take off. Achievements in the development of FWAVs demonstrate their potential for future applications, both in the military and civilian fields. In addition, further integration with other modes of locomotion, such as crawling, jumping, perching, self-wing-folding, and water-diving, can be a future direction of a FWAV to fully adapt the biologically locomotive strategies in nature, and to increase the range of applications.