Real-Time Trajectory Generation of a Quadrotor UAV with Load Suspended from a Pulley

Quadrotor UAV carrying a payload with a cable can be a prominent setup for aerial transportation. However, it is challenging for the suspended load system to navigate through tunnel-like obstacles if the vertical gap is narrower than the length of the cable. We aim to resolve this problem by adopting the pulley mechanism which controls the cable length. This paper presents a model predictive control based real-time trajectory generation algorithm for a quadrotor with its load suspended from a pulley, or the quadrotor-pulley system. We design a cost function that can be generally applied for avoiding obstacles with rectangular surfaces. Using the cost function, an optimal control problem is formulated, which is then solved by implementing model predictive control algorithm with sequential quadratic programming solver. We employ the state-of-the-art real-time iteration scheme to promote computational efficiency of the algorithm. The presented algorithm is demonstrated with simulations, where trajectories for the quadrotor-pulley system were successfully generated. Collision-free trajectories through tunnels with various heights and lengths were generated in real-time, thus validating the robustness of the algorithm.