Improving the Controller Performance of a Tilt-Rotor Octocopter by Compensating for the Tilt Angle's Dynamics

Abstract

This letter presents a novel control allocation compensator for a tilt-rotor octocopter using passive hinges, aimed at enhancing attitude control performance by accounting for the dynamic characteristics of the actuators. The introduction of a passive hinging mechanism results in a slower tilt angle response compared to servo-actuated systems, which, if overlooked, can significantly degrade controller performance. In this regard, the letter first models the arm's tilting dynamics and discusses its impact on control allocation errors. A two-part compensator is then introduced to address these dynamics: the first part adds a simple control loop to the control allocation module to quicken the tilt response; the second part re-allocates the thrust based on estimated tilt angles, leveraging the motor's rapid response to offset the slow response of the tilt angle. By simultaneously accelerating the tilt response and reallocating thrusts, the compensator minimizes control allocation error, thereby enhancing the accuracy of position and attitude control. The effectiveness of the proposed method is validated through both simulations and real flight experiments.