Relative motion modeling and control for a quadrotor landing on an unmanned vessel

This paper presents the design of an autopilot for autonomous landing of a quadrotor on an unmanned vessel. The problem of quadrotor landing was usually treated as a trajectory tracking problem, but in this paper, it is converted as a stabilization problem of relative motion to facilitate the controller design. A coupled six-degrees-of-freedom (6-DOF) non- linear relative motion model with four control inputs is established. The landing controller is divided into two parts, relative position controller(RPC) and relative attitude-altitude controller(RAC). RPC is proposed for use when the quadrotor is far away from the vessel, which is aimed at controlling the quadrotor to y to the vicinity of the unmanned vessel.RAC is used for the situation when the quadrotor is close to the vessel, which can control the quadrotor to land on the vessel steadily. To overcome the problem of nonlinear and strong coupling features of the relative system, a backstepping technique is applied in both RPC and RAC. The performance of the autopilot is demonstrated by computer simulations.