Attitude Control of Quad-Rotor Aircraft with Rudders

This paper researches the mathematical modeling and attitude control of four-rotor UAV with rudders. The structure of four-rotor with rudders is different from conventional four-rotor. The quaternion is used to describe the attitude of the aircraft in order to avoid the singularity. The mathematical model is derived by choosing reasonable coordinate systems and physical quantities, such that all physical quantities, including the control quantities, are expressed in the model explicitly. Since all state and control quantities in the model are nonlinear, a nonlinear controller is designed based on feedback linearization. The controller contains two feedback loops: the outer loop of attitude angle and the inner loop of angular velocity. Because of the nonlinear effect of the system, the inner loop feedback is coupled with the attitude angle, which is quite different from the traditional double loop feedback. The simulation results show that the designed control law can make the controlled quantities converge rapidly, and it is suitable for the situation where the attitude angle changes over a wide range.