Nonlinear Robust Controller for Miniature Helicopters Without Singularity.

A singularity-free nonlinear robust controller is proposed for miniature helicopters to accomplish trajectory tracking missions. The helicopter model is decomposed into a cascaded structure with some unmodeled dynamics. The controller development applies the hierarchical strategy. First, a position loop controller is designed based on a saturation control scheme using differential hyperbolic tangent functions, and criteria for choosing controller parameters are established to ensure the finite-time position tracking and to obviate singularity in the command attitude extraction. Singularity may also occur during the attitude tracking when the pitch of the helicopter reaches \pm \frac\pi 2. Based on a barrier Lyapunov function, an attitude loop controller is put forward with a backstepping technique, and an initial condition constraint for the nonsingular attitude tracking is deduced. Simulations illustrate the applicability of the proposed controller. [ABSTRACT FROM PUBLISHER]