Modeling and Control of a 6-DOF Multi-rotorcraft: Air-Ball
The Air-Ball project seeks to develop an omnidirectional, unmanned aerial vehicle with six degrees of freedom. The Air-Ball vehicle uses six propellers powered by six independent electric motors for propulsion and control. Each motor is attached to a hollow shaft that can rotate ±360° actuated by electric servos. Four of these propulsion shafts are configured in an orientation resembling a quad-copter, where the shafts are 90° apart. The other two propulsion shafts extrude perpendicular from each side of the plane of the quadcopter configuration. Under this unique configuration, Air-Ball is capable of decoupling the motion in the translational and rotational degrees of freedom, which brings great potential in spacecraft controls research and in using Air-Ball as a mapping or search tool. The highly nonlinear and over-actuated system poses a challenge for system modeling and controller design. To cope with this challenge, a modeling software, SimMechanics, was used to develop a flight simulation based on multibody physics. In addition, a mathematical model of Air-Ball was developed for designing a sliding mode controller. The sliding mode controller was integrated with the SimMechanics model to simulate the controller performance. Overall, the combination of sliding mode controller and the SimMechanics plant model produced multiple translation and rotation maneuver simulations. Uncertainties in the mathematical model were identified from the SimMechanics model and addressed appropriately. The following thesis provides a literature search on other six degrees of freedom vehicles, the mathematical model development, the SimMechanics model development, controller choice and design, and flight simulation results.