Tracking Control and Differential Flatness of Quadrotor with Cable-suspended Load

A new approach to tracking control of a quadrotor with a cable-suspended load is presented in this paper. The highly coupled nonlinear dynamics of 8 degrees of freedom quadrotor-load system is decoupled into 2 subsystem: a quadrotor attitude control subsystem and a double points link subsystem. Based on Lagrange equation, dynamical model is obtained. This system is proved to be differentially flat with the load position and the quadrotor yaw serving as the flat outputs. According to the relationship between flatness and feedback linearization, the system is transformed into a linear closed-loop system by an endogenous dynamic feedback. Then, trajectory tracking is carried out in closed loop based on Hurwitz stability criterion. Simulation results demonstrate the effectiveness of the controller.