Positionable Rotor Quadrotor: Dynamic Modeling and Adaptive Finite-Time Sliding-Mode Controller Design

This paper introduces a positionable rotor structure for a quadcopter allowing each of its rotors to be positioned independently in a finite course and in forward and backward movement to increase robustness against disturbances such as wind. At first, the quadrotor motion dynamics are analyzed, and its dynamic model is derived by calculating translational and angular momenta. A hybrid controller with dual interconnected units is designed to achieve acceptable performance. The primary unit determines the common quadruplet control inputs of the quadrotor by an adaptive finite-time sliding-mode algorithm for all the translational and rotational degrees of freedom. The secondary unit uses primary controller outputs to specify each rotor's suitable position to enhance the drone performance and robustness. Some correction steps are used to calculate more feasible rotor positions. Besides showing the proposed control system's performance, simulations verify the effectiveness of rotor positioning on the quadrotor stability in harsh conditions. For the case study, up to 70% increase in the capacity of disturbance rejection and an over 30% reduction in power consumption compared to conventional drones are observed.