Optimized adaptive variable exponent nonsingular terminal SMC for trajectory tracking of a quadrotor

This paper presents a novel adaptive nonsingular terminal sliding mode control (NSTSMC) strategy with a variable exponent approach for robust quadrotor attitude tracking under external disturbances. The proposed controller introduces, for the first time, an adaptive variable exponent NSTSMC framework that achieves practical fixed-time (FxT) convergence and robust performance without requiring prior knowledge of the disturbance bounds. Unlike existing FxT control methods, the proposed scheme employs an adjustable exponent that varies according to the system state’s proximity to the reference trajectory, leading to faster convergence and reduced control effort. Multiple adaptive switching control gains are designed for individual control axes, while the nominal controller parameters are optimized using the Sine Cosine Algorithm (SCA) to further minimize control effort. The proposed controller design enhances both transient response and steady-state accuracy, while guaranteeing practical FxT stability, which is rigorously established through Lyapunov theory. Simulation results and comparative studies validate the effectiveness of the proposed approach, demonstrating a reduction in tracking error of up to 74% and a decrease in control effort of 19.5% compared to state-of-the-art NSTSMC methods. Real-time experiments on a Quanser 3D Hover platform further validate the robustness, accuracy, and practical applicability of the proposed control scheme.