An output feedback attitude tracking controller design for quadrotor unmanned aerial vehicles using quaternion

In this paper, a quaternion based nonlinear output feedback tracking controller is developed to address the attitude and altitude tracking problem of a quadrotor unmanned aerial vehicle (UAV) which is subject to structural uncertainties and unknown external disturbances. A set of filters are introduced to provide estimation for the unmeasurable quadrotor UAV´s angular and translational velocity signals. The Lyapunov based stability analysis ensures that a semi-global asymptotic tracking result is achieved and all closed loop states remain bounded with a suitable choice of control gains.