Null-space-based path-following control for cooperative payload transport using multiple rotorcraft UAVs

This paper considers the problem of carrying a payload hanging through flexible cables from rotorcraft unmanned aerial vehicles (RUAVs), taking into account obstacle avoidance, even distribution of payload weight between the aircrafts, and formation shape. The simultaneous fulfillment of these objectives, prioritizing obstacle avoidance, is achieved by using a null-space-based control. In this approach the payload must follow a predetermined path to avoid possible oscillations. In addition, an accurate 6-DoF nonlinear dynamic model of a mini-helicopter and dynamic models for the cables and payload are included to consider a realistic scenario. Finally, simulation results show the good performance of the proposed approach.