This paper presents a fault tolerant approach for a coaxial octorotor regarding rotor failures. A complete architecture including error detection, fault isolation and system recovery is presented. The diagnosis system is designed with a nonlinear observer to generate residuals and an inference model to evaluate them and isolate the faulty motor. Once the motor failure is diagnosed, a recovery algorithm is applied. It uses the built-in hardware redundancy of the octorotor and compensates the loss of the failing motor by controlling its dual to keep a stable flight that allows the multirotor to continue its mission. This architecture is validated on real flights.

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This paper presents a fault tolerant control strategy based on an offline control mixing for an octorotor unmanned aerial vehicle (UAV) regarding several rotor failures. This strategy consists of a set of explicit laws, computed offline, each one dedicated to a fault situation. The corresponding law is selected according to the output of a fault detection and isolation (FDI) module. This module is designed with a non-linear sliding mode observer. The main advantage of this architecture is the deterministic character of the solution, its fast operation and the low computational load. The effectiveness of this approach is illustrated through real experimental application to a coaxial octorotor, where up to four motor failures are considered.

Local controllability and attitude stabilization of multirotor UAVs: Validation on a coaxial octorotor. Robotics and Autonomous Systems, Elsevier, 2017, 91, pp. AbstractThis paper addresses the attitude controllability problem for a multirotor unmanned aerial vehicle (UAV) in case of one or several actuators failures. The small time local controllability (STLC) of the system attitude dynamics is analysed using the nonlinear controllability theory with unilateral control inputs. This analysis considers different actuators configurations and compares their fault tolerance capabilities regarding actuators failures. Analytical results are then validated experimentally on a coaxial octorotor. A stabilization control law is applied on the coaxial configuration under one, two, three and four motors failures, when the system is controllable. Real-time experimental results demonstrate the effectiveness of the applied strategy.