Disturbance observer-based adaptive sliding mode control for variable dihedral and dual-mode yaw vectoring...

In this paper, a novel Disturbance Observer-Based Adaptive Sliding Mode Control (DOB-ASMC) architecture for a medium-size tricopter unmanned aerial vehicle (UAV) equipped with variable dihedral arms and dual-mode yaw vectoring is suggested with focus on the design, mathematical modeling, and experimental validation. The proposed tricopter architecture comprises mechanically reconfigurable dihedral angles (0°-30°) on its three arms and a hybrid tail rotor system capable of both conventional servo-deflection yaw control and thrust-differential yaw generation. This dual-mode yaw technique significantly improves torque bandwidth and agility in degraded conditions. The tightly coupled, nonlinear six-degree-of-freedom (6-DOF) dynamics coming from dihedral reconfiguration and rotor interaction with DOB-ASMC are presented. A nonlinear disturbance observer (NDO) is introduced for the estimation of time-varying external disturbances, including wind gusts, motor asymmetry, and structural flexibility, feeding compensatory signals into an adaptive sliding mode control law whose switching gain self-tunes based on estimated disturbance magnitude. A proof of Lyapunov stability analysis with finite-time convergence is presented for a sliding surface and ultimate boundedness of tracking error. Comprehensive simulation studies in MATLAB/Simulink with aerodynamic disturbance injection and hardware-in-loop (HIL) experiments on a custom 1.2 kg prototype have been done to show superior attitude tracking, robust yaw performance, and graceful degradation relative to classical PID, standard SMC, and backstepping controllers. The studies demonstrate that root mean square (RMS) tracking error is reduced by up to 63% and chattering is attenuated by 47% compared to conventional SMC under severe wind disturbances of 8 m/s.