A fail-safe algorithm in case of motor failure was developed, simulated, and tested. For practical fail-safe flight, the quadcopter may fly with only three or two opposing propellers. Altitude for two-propeller architecture was maintained by a PID controller that is independent from the inner and outer controllers. A PID controller on propeller force deviations from equilibrium was augmented to the inner controller of the three-propeller architecture. Both architectures used LQR for the inner attitude controller and a damped second order outer controller that zeroes the error along the horizontal coordinates. The restrictiveness, stability, robustness, and symmetry of these architectures were investigated with respect to their output limits, initial conditions, and controller frequencies. Although the three-propeller architecture allows for distribution of propeller forces, the two-propeller architecture is more efficient, robust, and stable. The two-propeller architecture is also robust to model uncertainties. It was shown that higher yaw rate leads to greater stability when operating in fail-safe mode.

中文翻译：

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用于具有电机故障的四轴飞行器的故障安全控制器架构

开发、模拟和测试了电机发生故障时的故障安全算法。对于实际的故障安全飞行，四轴飞行器可能只使用三个或两个相对的螺旋桨飞行。双螺旋桨架构的高度由独立于内部和外部控制器的 PID 控制器维持。将螺旋桨力偏离平衡的 PID 控制器扩展到三螺旋桨架构的内部控制器。两种架构都将 LQR 用于内部姿态控制器，并使用阻尼二阶外部控制器将水平坐标上的误差归零。研究了这些架构的限制性、稳定性、稳健性和对称性，包括它们的输出限制、初始条件和控制器频率。虽然三螺旋桨架构允许分配螺旋桨力，但双螺旋桨架构更高效、更稳健、更稳定。双螺旋桨架构对不确定性建模也很稳健。结果表明，在故障安全模式下运行时，更高的偏航率会带来更大的稳定性。