Control & Actuation

Multiplex Twinstar in autonomous flight



Quadrocopter with Engine Failure

Autel X-Star

Engine failure or structural damage to a propeller pose a serious threat for the operation of multicopters. A quadrocopter looses the ability to hover if a single actuator fails. The reason is a yaw torque, which can not be compensated for by the remaining propellers. The Institute of Flight Mechanics developed an emergency controller which aligns the thrust direction with a reference given by the RC-pilot utilizing the three available actuators. With the proposed controller the position of the corrupted quadrocopter can be maintained even though the vehicle turns with up to 6 rotations per second.

Using an Autel X-Star the controller was successfully demonstrated in flight. The approach enables emergency landings in case of engine failure preventing uncontrolled collisions in such a scenario.

Picture: © Autel Robotics



Control Allocation

Some vehicles have more actuators than physical degrees of freedom, for example to provide redundancy in case of a failure. However, the controller for such a vehicle needs some way to allocate its physical commands to each actuator. There are several approaches of varying complexity to solve this under-determined problem, but they can have unexpected results, especially when the commands are close to the physical maximum of the system.

The algorithm developed at the institute ensures full exploitation of the physical control space without changing the direction of the desired command. It was demonstrated on one of the institute’s octocopters by switching off one engine in-flight.
Control Allocation Algorithm, one engine out

The video below shows a real flight demonstration of a simulated engine failure that causes one rotor of the multirotor UAV to stop. Reconfiguration guarantees for safe operation of the over-actuated system in the presence of an engine failure.

  • Frangenberg, Michael; Stephan, Johannes and Fichter, Walter. 2015. Fast Actuator Fault Detection and Reconfiguration for Multicopters. AIAA Guidance, Navigation, and Control Conference (AIAA 2015-1766)


@2015 iFR - Flight Mechanics and Controls Lab


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