Virtual Nonholonomic Constraints-Based Motion Control for Underactuated UAV Slung-Payload Systems

The UAV slung-payload transportation system, characterized by highly nonlinear and coupled dynamics, poses a significant control challenge due to the two-degree underactuation of the tethered payload. This note investigates online trajectory generation and control for this system, focusing on the asymptotic stabilization of both the actuated UAV's positions and the unactuated payload's swings. First, we introduce a virtual nonholonomic constraint(VNHC) based approach to generate smooth UAV trajectories. This approach simplifies the design by operating on a lower-dimensional system, thereby bypassing the complexities of the original high-dimensional underactuated system. Second, a continuous fixed-time tracking controller is designed to drive the system dynamics onto the VNHC and to ensure its invariance. The rigorous asymptotic stability of the closed-loop system is analyzed using Lyapunov techniques and Barbalat's lemma. Numerical and experimental studies are conducted to evaluate the performance of the proposed approach.