Robust attitude tracking control for a variable-pitch quadrotor with uncertainties

Variable-pitch quadrotors have demonstrated their capability to enhance control performance and overcome limitations compared to conventional fixed-pitch quadrotors, while still facing challenges such as nonlinearity, couplings, uncertainties and so on. This article aims to address the robust attitude control problem of variable-pitch quadrotors afflicted with parametric uncertainties and unpredictable external disturbances. Initially, a practical actuator allocation strategy for the motor-propeller is proposed, followed by the development of a nonlinear robust attitude tracking controller capable of addressing all uncertainties. The effectiveness of the proposed controller in ensuring exponential stability of the closed-loop system, thereby driving the attitude tracking error to a small range within a finite time, has been substantiated. To evaluate the control performance, a hardware-in-the-loop testbed is constructed to conduct real-time experiments. The experimental results from attitude control case, comparative case, and position control case demonstrate that the designed motor-propeller allocation method and robust controller are effective in achieving a fast response and excellent control performance.