Fault-Tolerant Control of a Quadrotor Unmanned Aerial Vehicle with Single Rotor Failure in Dense Obstacle Environments.

Due to the motor degradation from long-term flight and the underactuated dynamics of quadrotor unmanned aerial vehicles (UAV), rotor failures are more likely to occur, posing significant challenges to stable flight. To address the impact of a single rotor completely failure, a quaternion-based decoupled degraded fault-tolerant control strategy is proposed to ensure accurate trajectory tracking performance of the quadrotor UAV. When a single rotor completely failure, the attitude control is intentionally degraded to retain altitude and attitude regulation capabilities in complex environments. To enhance robustness, a sliding mode observer (SMO) is designed to estimate and compensate for external unknown wind disturbances. Furthermore, to enable obstacle avoidance in three-dimensional environments, a geometric position controller integrated with the artificial potential field (APF) method is developed. The stability of the closed-loop system is rigorously analyzed using the Lyapunov method. Numerical simulation results demonstrate that the proposed control strategy provides strong robustness and high-precision pose tracking, even under complete single-rotor failure scenarios in complex environments. These findings suggest that the control framework is suitable for reliable autonomous flight missions under actuator efficiency degradation.