A novel quad-rotor configuration capable of attitude control through center of gravity variation

This paper considers the attitude control of rotor based unmanned aerial vehicles (UAVs) using center of gravity (CoG) variation. Towards this, a novel quadrotor attitude actuation system having movable control masses to vary its CoG is proposed. A detailed non-linear mathematical model is derived to capture the complex dynamics of this multi-body system - quad-rotor augmented with CoG varying actuators. The addition of CoG varying mechanism to a conventional quad-rotor leads to over actuation of the roll and pitch degrees of freedom. Therefore, control allocation is performed such that the roll and pitch degrees of freedom are controlled using CoG varying mechanism, whereas vertical motion and yaw stabilization is taken care of by the rotor angular speed control. Based on the developed mathematical model, an integral back-stepping controller is designed to stabilize and control the attitude and position of the proposed configuration. Further, the robustness of the designed controller and the proposed actuation mechanism is demonstrated through various simulations that are performed with measurement noise, and model and parameter uncertainties.