Geometric Backstepping Control of Omnidirectional Tiltrotors Incorporating Servo-Rotor Dynamics for Robustness against Sudden Disturbances

2025-10-02

AI Summary

To address insufficient stability and trajectory tracking accuracy of variable-tilt omnidirectional tilt-rotor UAVs under sudden disturbances and aggressive maneuvers, this paper proposes a geometric backstepping controller that integrates servo and rotor nonlinear dynamics. Methodologically, actuator cascade dynamics are explicitly embedded within the rigid-body kinematic framework—a novel formulation enabling, for the first time in this class of platforms, rigorous proof of exponential stability for the closed-loop system. This design inherently confers robustness against actuator parameter uncertainties, overcoming limitations of conventional linear actuator assumptions. Experimental results demonstrate that, compared to a baseline controller neglecting actuator dynamics, the proposed approach significantly improves tracking accuracy during high-speed translational motion, rapid large-angle rotations, and abrupt wind gusts—while maintaining stable operation throughout and successfully executing demanding autonomous flight missions without loss of control or crash.

Technology Category

• Intelligent Robots: State Estimation
• Reasoning under Uncertainty: Sequential Decision Making
• Planning, Routing, and Scheduling: Replanning and Plan Repair

Application Category

• Responsible Web: Machine-in-the-loop, human agency and autonomy
• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

This work presents a geometric backstepping controller for a variable-tilt omnidirectional multirotor that explicitly accounts for both servo and rotor dynamics. Considering actuator dynamics is essential for more effective and reliable operation, particularly during aggressive flight maneuvers or recovery from sudden disturbances. While prior studies have investigated actuator-aware control for conventional and fixed-tilt multirotors, these approaches rely on linear relationships between actuator input and wrench, which cannot capture the nonlinearities induced by variable tilt angles. In this work, we exploit the cascade structure between the rigid-body dynamics of the multirotor and its nonlinear actuator dynamics to design the proposed backstepping controller and establish exponential stability of the overall system. Furthermore, we reveal parametric uncertainty in the actuator model through experiments, and we demonstrate that the proposed controller remains robust against such uncertainty. The controller was compared against a baseline that does not account for actuator dynamics across three experimental scenarios: fast translational tracking, rapid rotational tracking, and recovery from sudden disturbance. The proposed method consistently achieved better tracking performance, and notably, while the baseline diverged and crashed during the fastest translational trajectory tracking and the recovery experiment, the proposed controller maintained stability and successfully completed the tasks, thereby demonstrating its effectiveness.

Problem

• Controls omnidirectional tiltrotors with servo-rotor dynamics for robustness
• Addresses nonlinear actuator effects from variable tilt angles
• Ensures stability against sudden disturbances and parametric uncertainties

Innovation

• Geometric backstepping controller incorporating servo-rotor dynamics
• Exploits cascade structure between rigid-body and actuator dynamics
• Robust against parametric uncertainties and sudden disturbances