Using iterative LQR to control two quadrotors transporting a cable-suspended load

Abstract

Abstract This paper is focused on the tracking control problem of two quadrotors carrying one cable-suspended payload. The paper main contributions include a dynamic model constructed by Euler-Lagrange equations for this system, an iterative linear quadratic regulator (iLQR) optimal controller, which is able to track the desired trajectory for the payload position and attitude and a simulation for tracking a spiral trajectory. The nonlinear dynamic model is linearised by considering the angles of connected links from the payload to each quadrotor as the equilibrium point. The iLQR control algorithm is developed for the full system consisting of two quadrotors connected with a point mass load in order to improve the tracking performance and avoid the slung load swing. The simulation results demonstrate that the iLQR approach is able to improve the tracking performance compared with an LQR controller.