Design and Development of Scissorbot: A Novel Mid-Flight-Span-Reducing Quadcopter

Abstract

This article presents the design and development of Scissorbot, a novel mid-flight reconfigurable geometry quadcopter that reduces its lateral-span using a single servomotor coupled with a compact bevel differential gearbox. Scissorbot possesses unique practical features, including geometrical symmetricity, fault tolerance to the servomotor, and the gearbox’s weight-scalability. Scissorbot achieves significant lateral-span reduction without the risk of propeller tip collision by positioning adjacent propellers in different planes. To the best of author’s knowledge, the maximum lateral-span reduction surpasses any controllable morphing quadcopter reported in the literature. This work derives a detailed attitude dynamics model and conducts a theoretical analysis of the gearbox. The attitude control is accomplished through the implementation of a robust controller, which exhibits exponential tracking, even in the presence of parametric uncertainties, and propeller aerodynamics disturbances. A velocity controller augments the attitude controller. The control allocation loop is parametrized to adapt to the reconfiguration process. Various evaluations, encompassing multibody simulations and hardware flight experiments, assess Scissorbot’s performance. The results unequivocally demonstrate controller’s excellent tracking in simulations and on the hardware prototype across all scenarios. Moreover, the experiments validate the fault tolerance feature of Scissorbot. In addition, a comprehensive study is performed to analyze the scalability of the current gearbox for higher-weight Scissorbot prototypes.