On Robust Stabilization of Motion of a Quadrotor with Slung Load

One of the important tasks that can be performed by quadrotors is the transportation of various payloads. If the load is suspended from the quadrotor and can move relative to the quadrotors body, this motion must be taken into account in the control system, in particular, in order to suppress and prevent unwanted oscillations of the load. In the present paper, a mechanical system is considered that consists of a quadrotor and a load suspended to it with a weightless rod. It is assumed that the cross-sectional area of the load is large enough so that the aerodynamic forces acting on it cannot be neglected. It is known that for a number of shapes of payload casing, this aerodynamic force is not reduced only to the drag force, but also contains a component orthogonal to the drag force, that is, the lift force. In order to these forces, the quasi-steady approach is used. At the same time, accurate information about the aerodynamic capabilities for each particular payload is, generally speaking, not available. However, it is known that the values of aerodynamic coefficients for a fairly wide class of body shapes are lie in a specific range. Here we discuss the problem of developing the quadrotor control that would ensure robust stabilization of the ascent and descent of the system in the conditions of incomplete information about the aerodynamic load. A method is proposed for constructing the quadrotor control for robust stabilization of uniform vertical ascent and descent of the system as a whole. It is shown that this control ensures stabilization of the target mode within a fairly wide range of system parameters. Restrictions on the target speed of quadrotor motion are determined, violation of which makes the robust stabilization impossible.