Suspended Load Path Tracking by a Tilt-rotor UAV*

This paper deals with the load transportation problem by a tilt-rotor unmanned aerial vehicle. Most approaches address the subject by formulating the system dynamics from the UAV's point of view, with the load's behavior described with respect to it. Difficulties arise if control tasks are given for the load, since the suspended load coordinates do not appear explicitly in the mathematical formulation. A novel approach is proposed, based on the formulation of the system dynamics using position and orientation of the load as generalized coordinates. The equations of motion are developed in detail, yielding a highly coupled state-space representation. It is shown that linear techniques are sufficient for path tracking of the load at low accelerations, even when subject to external disturbances and incomplete, noisy information about the state vector is available. Simulation results are presented in order to validate the proposed approach.