Adaptive finite-time observer-based sliding mode control for a QUAV attitude tracking with external disturbances

Quadrotor unmanned aerial vehicles (QUAVs) are critically dependent on high-precision attitude control, whose performance is frequently compromised by parametric uncertainties and external disturbances. In this paper, an adaptive finite-time disturbance observer (AFTDO) is introduced, which dynamically recalibrates gain in response to time-varying disturbances, eliminating the need for a priori knowledge of disturbance bounds. Coupled with a fast nonsingular terminal sliding mode control (FNTSMC) strategy, the AFTDO-FNTSMC framework is developed to ensure finite-time convergence of attitude tracking errors to zero, while significantly attenuating chattering and enhancing robustness against observation inaccuracies. Both estimation and tracking errors are proved to converge within a finite time. Comparative simulations validate its superior tracking performance and enhanced disturbance estimation.