Robust altitude tracking of a miniature helicopter UAV based on sliding mode

This paper focuses on simple heave dynamics of helicopter UAV for autonomous operations to achieve efficient control scheme based on sliding mode methodology for accurate altitude tracking under both matched and unmatched disturbances. Under fast changing dynamics of the UAV, a control law is developed that provides robustness against uncertainties, parameter variations and perturbations for accurate hovering conditions. The controller guarantees the asymptotic stability of the origin in finite time and the stability of the law has been proved mathematically. Further, efforts are made to smoothen the control signal by making continuous approximation of the discontinuous function in the control law using hyperbolic tangent function.