Abstract : This paper addresses the issue of flight safety and
reliability of unmanned multirotor helicopters. New applications
involve the use of such flying platforms to perform inspection of
industrial facilities, bridges, dam walls, etc. In this context, the
multirotor helicopter is teleoperated by a distant human user. 1
The capability of fault-tolerance against rotor or motor is a
major asset to guarantee the success of the mission and the
safety of the surrounding environment. This paper contributes
to fault-tolerant flight of multirotor helicopter with the following
four points. First, given the configuration of the multirotor
vehicle, this paper shows how to calculate the maximum torques
that can be produced on each vehicle axis. Second, a method
to investigate the static controllability of the vehicle in any
arbitrary fault configuration is described. Third, a control
allocator for multirotor systems is developed with performance
going beyond performance obtained with classical methods, such
as the pseudo-inverse method. The proposed control allocator
is indeed capable of exploiting the whole attainable control
set. Fourth, this control allocator is fault-tolerant, as it can
efficiently cope with the loss of one or more actuators.
The control allocation problem is formulated as a parametric
program and solved for an explicit solution, which is stored
in lookup tables. Therefore, the control allocator requires very
low computational power and immediately provides an optimal
solution to the torque commands issued by the flight controller.
The performance of the control allocator is evaluated on a
real six-rotor helicopter. Finally, based on the real experiments,
the paper investigates 1) the impact of faults and 2) the
influence of the reconfiguration delay on the flight stability.
These experiments show that this control allocation strategy
successfully increases flight performance and maintains stability
of the vehicle in case of actuator(s) total failure.