Robust position hold control of hexarotor UAVs

This paper presents a practical robust position hold control design for hexarotor unmanned aerial vehicles (UAVs) under the effects of uncertainties (equivalent disturbance) which contain external disturbances, nonlinear dynamics, coupling, and parametric uncertainties. The proposed controller has three main loops which are position-xy, altitude, and attitude loop. Thenominal linear time-invariant controller is designed for each loop based on cascade proportional-integral-derivative (PID) method while a robust compensator based on second order robust filter is added on attitude loop in order to improve the attitude tracking performance when the hexarotor leaves the nominal conditions due to presence of uncertainties. The experimental results prove the effectiveness of proposed controller to reduce and bind the attitude tracking errors at certain boundaries and demonstrate the ability of controller to hold the vehicle position in the outdoor flight environment.