Research on Trajectory of Quadrotor Elastic Suspension Load System Based on Differential Flatness and RRT* Algorithm

The paper introduces a method for trajectory planning of quadrotors with elastic suspension load systems in complex environments. The method combines differential flatness and RRT* algorithm to address challenges such as large load swing due to obstacle avoidance, elastic rope suspension load, and significant trajectory corner changes. Firstly, a dynamic model of the elastic suspension load system is established and shown to possess differential flatness. The load’s position variable is chosen as the flat output, enabling the representation of all other system state variables using the flat output and its derivatives, thereby reducing solution complexity. Secondly, the RRT* obstacle avoidance algorithm incorporates a target bias mechanism to guide sampling points towards the target point, improving convergence speed. During random tree node expansion, considerations include the elastic rope constraint and load swing angle constraint between the quadrotor and the load to prevent collisions with obstacles. Finally, a sixth-degree B-spline curve is utilized for the purpose of smoothing and optimizing the trajectory. This method has been compared with the $\mathrm{A}^{*}$ algorithm, and simulation results show that the proposed method has better anti swing effect.