Flight control of a tilt-rotor quadcopter via sliding mode

In contrast to the conventional underactuated quadrotor, an over-actuated tilt-rotor quadcopter equipped with four tilting rotors can fly the arbitrary position trajectory while maintaining the desired attitude. We study the translational and rotational dynamic model for the tilt-rotor quadcopter associated with disturbances and uncertainties. Using the tilting rotors, we design two sliding mode controls to improve the robustness and performance of the quadcopter system: a first-order sliding mode to exploit the structural property of the rotational dynamics and a second-order sliding mode to avoid the chattering in the translational dynamics. From Lyapunov stability theorem, we show that the proposed control schemes can ensure the asymptotical stability of the error dynamics in terms of positions and attitudes for the tilt-rotor quadcopter. The results of numerical simulations demonstrate that the proposed sliding mode control can accomplish the goal of tracking the desired trajectory and keeping the proper attitude under parametric variations and external disturbances.