This paper presents a novel actuation model and control allocation strategy for a redundantly-actuated multirotor unmanned aerial vehicle (UAV), referred to as the omnicopter. With an unconventional configuration, the omnicopter's eight propellers are able to produce all the six components of net force/torque, with two degrees of actuation redundancy. This enables the vehicle to execute motion trajectories unattainable with conventional underactuated multi-rotors. A new inverse actuator model is proposed that accounts for the significant interactions between propeller airflows by relating their output thrust forces to their input motor commands. Actuation redundancy is resolved by solving a convex constrained optimization problem. Its solution yields the most power efficient set of propellers thrusts that would produce a required net force/torque, while respecting the propeller thrust limits. When the required force/torque is infeasible due to the thrust limits, the solution would minimize the norm of the error between the desired and actual net force/torque vectors. Experimental results demonstrate the effectiveness of the proposed model and control allocation strategy.

A provably stable decentralized control scheme is proposed to allow multiple conventional quadcopters carry a cable-suspended payload. The method exploits a fundamental energetic passivity property of the combined drones, cables, and payload system to stably move the payload from its origin to destination. This is achieved without making any assumption about the status of the cables tension during the flight, and any measurement from the payload. The controller is decentralized in the sense that inter-drone communication of feedback measurements is not required. Motion stability is demonstrated via a Lyapunov analysis. The proposed controller is successfully implemented on a three-drone payload transport system in an indoor environment, using measurement from an optical tracking systems and the drones on-board IMUs.