FAST-Hex—A Morphing Hexarotor: Design, Mechanical Implementation, Control and Experimental Validation

Abstract

We present FAST-Hex, a micro aerial hexarotor platform that allows to seamlessly transit from an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">underactuated</i> to a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fully actuated</i> configuration with only one additional control input, a motor that synchronously tilts all propellers. The FAST-Hex adapts its configuration between the more efficient but underactuated, collinear multirotors, and the less efficient but full pose tracking, which is attained by noncollinear multirotors. On the basis of prior work on minimal input configurable micro aerial vehicle, we mainly stress three aspects: Mechanical design, motion control, and experimental validation. Specifically, we present the lightweight mechanical structure of the FAST-Hex that allows to only use one additional input to achieve configurability and full actuation in a vast state space. The motion controller receives as input any reference pose in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbb {R}^3\times \mathrm{SO}(3)$</tex-math></inline-formula> (3D position + 3D orientation). Full pose tracking is achieved if the reference pose is feasible with respect to actuator constraints. In case of unfeasibility, a new feasible desired trajectory is generated online giving priority to the position tracking over the orientation tracking. Finally, we present a large set of experimental results shading light on all aspects of the control of the FAST-Hex.