Load-Distribution-Based Trajectory Planning and Control for a Multilift System

This paper studies a load-distribution-based trajectory planning and control strategy for a hierarchically controlled multilift system. It proposes a method that simultaneously plans payload trajectory and cable forces while satisfying path and force constraints and minimizing the difference in cable forces. A direct collocation method is used to solve the formulated planning problem. Then, a neighboring feedback law is designed to equalize the cable tension load distribution during flight. Here, the system dynamics are linearized about the nominal path. An linear-quadratic regulator (LQR) controller is then designed for the system to track the planned trajectory. Simulations of payload transport showed that even with the effect of disturbances (i.e., wind gusts), cable tensions are more evenly distributed with the proposed approach. Finally, indoor flight tests were performed to validate the proposed approach. Results showed that the system has reduced energy consumption compared with the case without planning based on load distribution. The rotorcraft achieved less average total power and near-equal energy consumption.