Model Predictive Control of a Multi-Rotor with a Suspended Load for Avoiding Obstacles

This paper investigates a multi-rotor with a suspended load in perspectives of 1) real-time path planning, 2) obstacle avoidance, and 3) transportation of a suspended object. A suspended load cannot be controlled with conventional controllers designed for nominal multi-rotors due to the dynamic coupling between the multi-rotor and load. Although several control and planning algorithms have been proposed based on elaborately derived dynamic equations, most existing studies separate control and path planning problems by following pre-defined trajectories after trajectory generation. Moreover, many state-of-the-art trajectory generation algorithms cannot work real-time for a system with high degrees of freedom, which makes it not suitable to operate the system in dynamic environments where obstacles appear abruptly or move unexpectedly. With this in mind, we apply Model Predictive Control (MPC) with Sequential Linear Quadratic (SLQ) solver to compute feasible and optimal trajectory real-time and to operate a multi-rotor with a suspended load in dynamic environments. We design an obstacle-avoidance algorithm suitable for the current platform flying in cluttered environments. Flight experiments shows that the proposed algorithm successfully controls the multi-rotor and allows to avoid obstacles simultaneously.