Nonlinear robust attitude tracking control of an underactuated 3 degree-of-freedom helicopter

This paper proposes a new asymptotic attitude tracking controller for an underactuated three degree-of-freedom laboratory helicopter system. The nonlinear robust control law is developed through a modified inner-outer loop approach, and is free of chattering. The controller requires very limited knowledge of the system dynamic model while achieving good robustness with respect to system parametric uncertainties. A Lyapunov based stability analysis shows that the proposed algorithms can ensure asymptotic tracking of the helicopter's elevation and travel angles, while keeping the stability of the closed loop system. Numerical simulation results demonstrate that the controller has good tracking performance, and requires few model knowledge.