Stability and control issues of multirotor suspended load transportation: An analytical closed–form approach

In the present paper a fully-analytical framework is outlined to analyze the effects of cable-suspended loads on multirotor platforms. In particular, the dynamics of an isolated vehicle is first investigated by including the complete model of the electric propulsion system. Then, system description is extended to the load, which introduces non-actuated degrees of freedom and is suspended through a linear-elastic cable. In order to provide the complete slung-load system with a closed-loop desired behavior, an auxiliary controller is proposed to recover or improve the initial multirotor dynamic properties, while stabilizing load oscillations. To this end, closed-form equations are derived to design the auxiliary controller gains, based on the knowledge of a limited set of parameters. A test case is proposed relative to a commercial-off-the-shelf hexarotor whose electrical propulsion system has been characterized by an experimental campaign performed at University of Bologna premises.