Decoupled translational and rotational flight control designs of canted-rotor hexacopters

The mainstream designs of the multi-rotor UAVs typically arrange their motors and propellers near or in the same plane, imposing limitations on their control maneuvers due to under-actuation. The limited control maneuvers cause the multi-rotors to have to pitch and roll in order to perform lateral translations. These multi-rotor aerial vehicles also lose the capability of keeping their center-of-mass stationary in the air while rotating by a certain pitch or roll angle due to the thrusts generated along rotated vertical axis in the body frame. This paper presents the mathematical model of a hexacopter with rotor-axes tilted to enhance the control maneuverability of conventional multi-rotor UAVs. Based on the Newton-Euler formalism of dynamics, we propose the path tracking controller and the tilt-hovering controller for cantedrotor hexacopters. First, the path tracking controller decouples lateral movements from pitch and roll rotations of the vehicle. Second, the tilt-hovering controller stabilizes the position of the center of mass of the vehicle as well as its orientation while it is rotated by a certain pitch or roll angle. Numerical simulations are performed to corroborate the mathematical model and control designs, and to compare with the performance of conventional multi-rotor UAVs.