Tilt-rotor quadcopters are a novel class of quadcopters with a servo motor attached on each arm that assist the quadcopter's rotors to tilt to a desired angle thereby enabling thrust vectoring. Using these additional tilt angles, this type of a quadcopter can be used to achieve desired trajectories with faster maneuvering and can handle external disturbances better than a conventional quadcopter. In this paper, a non-linear controller has been designed using sliding mode technique for the pitch, roll, yaw motions and the servo motor tilt angles of the quadcopter. The dynamic model of the tilt-rotor quadcopter is presented, based on which sliding surfaces were designed to minimize the tracking errors. Using the control inputs derived from these sliding surfaces, the state variables converge to their desired values in finite-time. Further, the non-linear sliding surface coefficients are obtained by stability analysis. The robustness of this proposed sliding mode control technique is shown when a faulty motor scenario is introduced. The quadcopter transforms into a T-copter design upon motor failure thereby abetting the UAV to cope up with the instabilities experienced in yaw, pitch and roll axes and still completing the flight mission. The dynamics of the T-copter design and the derivation of the switching surface coefficients for this re configurable system are also presented.
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