Chattering-free Sliding Mode Control for Position and Attitude Tracking of a Quadrotor with a Cable-Suspended Load

There are diverse applications in industry, agriculture and logistics which can benefit from the use of quadrotor Uncrewed Aerial Vehicles (UAVs) with cable-suspended payloads. Their control is a challenging topic, given the nonlinear and underactuated dynamics of the UAV and the oscillations of the cargo. In this work, we propose a chattering-free sliding mode controller (SMC) for position and attitude tracking of a quadrotor with a cable-suspended payload. Firstly, the model of the UAV and the load is derived via Lagrangian approach in matrix form. Then, the system is divided into two subsystems and four sliding mode controllers are designed. The chattering effect is eliminated via approximation of the signum function with a saturation function. Moreover, our approach permits computation of the sliding surface coefficients using a simple linearization of the dynamic model and Hurwitz analysis. The stability of the closed-loop controller is proven via Lyapunov theory and its effectiveness is validated through simulations. The proposed SMC allows to track the desired references when a quadrotor of 1.1 kg performs non-aggressive maneuvers, transporting a payload of 0.2 kg with a cable of 1 m. In this scenario, our approach ensures that the oscillations of the load are always smaller than 4.6 degrees.