This paper presents a cascade-modified uncertainty and disturbance estimator (CMUDE)–based controller. The attitude-tracking performance of a quadrotor would be greatly degraded due to two factors: (1) a nonideal actuator and (2) an exogenous disturbance. Based on these factors, an actuator model is accurately identified using a thrust test platform. Then, a cascade-structured CMUDE controller is designed through the backstepping method, so the disturbances from different channels can be separately dealt with. The idea of the uncertainty and disturbance estimator (UDE) is then applied to dynamically compensate for not only the exogenous disturbance but also the time delay in the actuator dynamics. Benefitting from that, the problem of mismatched disturbances is solved by defining virtual control inputs; furthermore, the nonlinear term in the attitude kinematics is included in the model uncertainty to be canceled instead of being ignored. When tracking attitude commands, the exogenous disturbance and model uncertainty along with the time delay of the actuator are estimated and compensated for by the proposed controller, so the performance of the disturbance rejection is significantly improved while maintaining a quick response to the rapidly changing commands. To verify that, the proposed controller is implemented on a quadrotor platform to carry out exhaustive experiments and compared with the mainstream cascade PID (CPID) controller, the classic UDE-based controller, and the latest modified-UDE (MUDE)–based controller. The results show that our control strategy achieves a better disturbance rejection and more accurate tracking performance than other controllers.

Distributed electronic propulsion (DEP) aircraft with vertical take-off and landing (VTOL) ability mostly equipped with multiple redundant tiltable propulsors, which are used to provide not only thrusts, but also control torque in all flight mode. The features make the control allocation problem of these aircraft both complex and important. Therefore, this paper proposes: (і) a prototype platform for DEP VTOL aircraft that allows researchers to design and analyse control allocation strategies, and (іі) a uniform hierarchical control allocation method that can be adapted to both MC and FW modes. The platform contains ten fully actuated thrusters, which are distributed in the scaled geometry of a typical DEP-VTOL aircraft. The proposed control allocation strategy uses hierarchical structure to avoid high-dimensional matrix operations for the redundant actuators. The additional constraints on the thrust and tilt angles of the actuators are addressed by adopting cascade generalized inversion (CGI) to force decompensation (FD)-based methods by a coordinate transformation. A novel smooth strategy through Schur Complement is also presented to achieve steady and smooth transition from MC to FW mode. Finally, the proposed method is implemented in the authors' novel platform in both simulations and flight experiments to demonstrate its effectiveness and smoothness.

Distributed electric propulsion technology has great potential and advantage in the development of drones. In this paper, to study the slipstream effect of distributed propeller, the actuator disk method was used to verify a single propeller, and the calculated thrust was in good agreement with the test results. Then, based on the actuator disk method, the influence of different installation positions on the slipstream effect was studied, and the distributed propeller layout was optimized by genetic algorithm. The analysis results showed that lift of the wing will be larger when the propellers are higher than the wing. When the relative height between the propeller and the wing is zero, the drag is the lowest. The influence of disk diameter on the slipstream is that the larger the diameter is, the higher the lift force and the drag force are. The slipstream effect of the optimized propeller distribution improves the lift-drag ratio of the wing, by 108.5% in the initial lift-drag ratio.

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