Observer-based improved robust control design for a serially reconfigurable quadrotor

Recent advances in aerial robotics have led to the development of variable geometry platforms, such as the serially reconfigurable quadrotor (SRQ), which enhance flexibility, adaptability and mission versatility. However, controlling such morphologically adaptive systems remains a significant challenge due to time-varying parameters, strong nonlinearities, structural asymmetries and modelling uncertainties introduced by reconfiguration. To overcome these challenges, this paper presents a comprehensive nonlinear dynamic model that accurately describes the SRQ behaviour while accounting for variations in the moments of inertia, their time derivatives and aerodynamic effects. Based on this model, a geometric simplification is proposed to enable the synthesis of a robust control framework that integrates an improved power rate reaching law (IPRRL) within a fast terminal sliding mode controller (FTSMC) combined with a finite time disturbance observer (FTDO). The proposed control scheme guarantees fast finite-time convergence, effective chattering suppression and robustness to external disturbances. Moreover, the controller and observer parameters are optimally tuned using the whale optimisation algorithm (WOA). Simulation results demonstrate that the proposed IPRRL–FTSMC framework achieves superior tracking precision, enhanced robustness and substantial chattering reduction compared with conventional sliding mode control (SMC) and FTSMC controllers. These results confirm the effectiveness and reliability of the proposed control approach for reconfigurable aerial robotic systems.