Toward Dexterous Flapping Flight: Effective Large Yaw Torque Generation by 2×2-Degrees-of-Freedom Flapping Wings

Abstract

Through the efforts of robotic engineers and inspired by the flapping flight of smaller creatures (e.g., insects and hummingbirds), the untethered stable hovering of flapping micro-aerial vehicles (FMAVs) has been achieved. Now, engineers are evaluating how to improve the mobility of these vehicles. The maneuverability of insects and birds in flight, such as their sharp turns and their takeoffs and landings from vertical walls, is what researchers originally expected from FMAVs. However, in previous studies, just one active (or one active plus one passive) degree of freedom (DoF) was given to the main actuation of the wing, and the range of movement of the wings was small. In addition, the magnitude of the attitude control torque that could be generated was relatively small when compared with multi-rotors. However, with the recent developments of small motors and drive-circuit technology, the realization of untethered flight by FMAVs equipped with four or more motors seems possible. This study utilized numerical calculation to investigate the advantage of a flapping-flight robot equipped with two pairs of left and right wings capable of stroke and twisting movements with two independent DoFs ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2\times 2$</tex> -DoF FMAV). The results of the numerical studies confirmed that, compared with the split-factor method widely used in past studies, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2\times 2$</tex> -DoF FMAV can generate higher yaw torque without the need for additional large driving torque. This shows that various agile flight functions are possible.