Quadrotor Upset Recovery after Rotor Failure

A fault-tolerant controller is presented that is able to recover a quadrotor from an upset condition in the case of a single rotor failure. With only 3 rotors the quadrotor is not fully controllable anymore, however by using precession the quadrotor can be made controllable again in roll and pitch. A step-by-step recovery strategy is proposed in which controllability is actively recovered before recovery of attitude and altitude. Control allocation is based on the Incremental Non-Linear Dynamic Inversion (INDI) principle and takes rotor saturation into account by solving a constrained quadratic optimisation problem. The controller is validated in a real life test environment where the quadrotor is thrown into the air with only 3 propellers from which it has to recover using the techniques presented in this paper.Aerospace Engineerin