Attitude stabilization controller for quadrotors based on the unit quaternion

This paper addresses the attitude stabilization problem of a flying robot with four rotors. We propose an alternative attitude dynamic model based on the unit quaternion. The proposed dynamic model resembles the equation of motion of a four degrees of freedom robot manipulator and shares similar properties. If the desired attitude is constant, we show that a PD controller renders the equilibrium point of the closed-loop dynamics exponentially stable. The validity of the dynamic model and effectiveness of the controller were assessed by experimental results on a small quadrotor.