Uniform Passive Fault-Tolerant Control of a Quadcopter with One, Two, or Three Rotor Failure

This study proposes a <italic>uniform</italic> <italic>passive</italic> fault-tolerant control (FTC) method for a quadcopter that does not rely on fault information subject to one, two adjacent, two opposite, or three rotor failure. The <italic>uniform</italic> control implies that the <italic>passive</italic> FTC is able to cover the condition from quadcopter fault-free to rotor failure without the need for controller switching. To achieve the purpose of <italic>passive</italic> FTC, the fault of rotors is modeled as a lumped disturbance acting on the virtual control of the quadcopter system. The estimated disturbance is used directly in the <italic>passive</italic> FTC. At the same time, a modified controller structure is designed to achieve the passive FTC ability for two and three rotor failure. To avoid the control allocation switching from the fault-free control to the FTC, a dynamic control allocation is used. In addition, the closed-loop stability is analyzed in the presence of up to three rotor failure. To validate the proposed <italic>uniform</italic> <italic>passive</italic> FTC method, outdoor experiments are performed <italic>for the first time</italic>, which have demonstrated that the hovering quadcopter is able to recover from one rotor failure using the proposed controller and resume its mission even if two adjacent, two opposite, or three rotors fail, without the need for any rotor fault information or controller switching. Experimental results can be viewed in this video: <uri>https://youtu.be/N1OudPXFXnE</uri>. Source code is placed on <uri>https://github.com/RflyBUAA/DegradedControl.git</uri>