Adaptive Backstepping Sliding Mode Control of Coaxial Octorotor Unmanned Aerial Vehicle.

In this paper, an adaptive backstepping scheme based on sliding mode control method is presented for attitude and altitude tracking control of a coaxial octorotor. The dynamical model of the coaxial octorotor is presented and according to design nature of the control scheme, the dynamical model is divided into three cascaded units: 1) under-actuated unit; 2) fully actuated unit; and 3) rotors thrust force unit. Adaptive backstepping control is then designed for all three units by means of a recursive process using sliding surfaces. The proposed scheme not only stabilizes the given system but also tracks the desired trajectory without any significant tracking error. The stability analysis of the complete system is presented using a Lyapunov stability theory. The results demonstrate the effectiveness of the proposed controller and also show that the proposed controller manages to attain good tracking performance with stabilization of octorotor.