H∞ control of an overactuated tilt rotors quadcopter

In recent years, unmanned aerial vehicles (UAVs) have acquired an increasing interest due to their wide range of applications in military, scientific, and civilian fields. One of the quadcopter limitations is its lack of full actuation property which limits its mobility and trajectory tracking capabilities. In this work, an overactuated quadcopter design and control, which allows independent tilting of the rotors around their arm axis, is presented. Quadcopter with this added tilting mechanism makes it possible to overcome the aforementioned mobility limitation by achieving full authority on torque and force vectoring. The tilting property increases the control inputs to 8 (the 4 propeller rotation speed plus the 4 rotor tilting angles) which gives a full control on the quadcopter states. Extensive mathematical model for the tilt rotor quadcopter is derived based on the Newton-Euler method. Furthermore, the feedback linearization method is used to linearize the model and a mixed sensitivity H-infinity optimal controller is then designed and synthesized to achieve the required performance and stability. The controlled system is simulated to assure the validity of the proposed controller and the quadcopter design. The controller is tested for its effectiveness in rejecting disturbances, attenuating sensor noise, and coping with the model uncertainties. Moreover, a complicated trajectory is examined in which the tilt rotor quadcopter has been successfully followed. The test results show the supremacy of the overactuated quadcopter over the traditional one.