Flying with Five: Design of a Motor Failure-Tolerant Control System for Hexacopters

Abstract

A motor failure-tolerant control system for generic hexacopters is presented. An optimal controller is developed for the hexacopters using a Linear Quadratic Regulator. Though the controller relies on linear dynamic equations, it uses gain scheduling to handle nonlinearities presented by a varying yaw angle. Several matrices are calculated to serve as linear trans-formations from high-level controller commands to commands to available motors. These matrices are calculated for the nominal hexacopter, hexacopters with one motor failure and bidirectional motors, and hexacopters with one motor failure and unidirectional motors. A parity relation-based fault detection and identification scheme is developed by taking ad-vantage of the linear relationship between angular rates and motor commands. The fault detector is able to robustly detect motor failures at various states of flight of the hexacopter model. Simulation results are used to tune the controllers and fault identifier and demon-strate the validity of this approach. An approach to adapting the Pixhawk flight controller to be motor-failure tolerant for hexacopters is outlined.