A back-stepping control strategy for the Tri-rotor UAV

Over the last decade, the use of Unmanned Aerial Vehicles (UAVs) has increased dramatically in both military surveillance and in civilian search and rescue operations. In this paper, we focus on the Tri-rotor UAV. We start by developing a model for a Tri-rotor UAV where our objective is to enable the rotor-craft to stabilize itself automatically at any desired hovering position. The Tri-rotor is composed of three rotors which are equidistant from its center of gravity. In contrast to a Quad-rotor, the rotors in a Tri-rotor introduce a destabilizing reaction torque to the system. This aspect of the Tri-rotor provides additional modeling challenges as compared to the Quad-rotor. The Tri-rotor is modeled using the Euler-Lagrange formalism. The speed of the rotors and tilt angle of one of the rotors constitute the four control inputs. The model acts as an underactuated one, as the model is a 6 Degree Of Freedom (DOF) model with only 4 external inputs. For the stabilization of the model, a back-stepping non-linear control is implemented, and the proposed controller is also analyzed by simulations.