Attitude control research for quad-rotor UAV

Quad-rotor helicopter is a popular platform for unmanned aerial vehicle (UAV) research due to its simplicity of structure and maintenance as well as the capability of hovering and vertical take-off and landing. The attitude controller is of great importance since it ensures the vehicle to keep balance and perform the desired maneuver. In this paper, sliding mode controller for attitude regulation is designed based on variable structure theorem according to the mathematical model of the 3-DOF Quanser hover system. The control objective of the attitude controller is to asymptotically track the different demanded signals, even if there exist unknown disturbances. Considering the chattering existing in the sliding model control system, the high-slope saturation function is utilized instead of the sign function. To validate the effectiveness and efficiency of the proposed method, the comparison among sliding mode, backstepping and PID methods is carried out. The results from both digital simulations and experiments on the hover system show that the sliding mode control law can perform adequately as an attitude controller in terms of better tracking performance and robustness compared with the other two methods.