Ground-Effect-Aware Modeling and Control for Multicopters

2025-06-24

AI Summary

To address control errors, altitude oscillations, and aerodynamic model mismatch induced by ground effect during low-altitude multirotor flight, this paper develops a high-fidelity dynamical model incorporating external torques, rotor drag, and dynamic variations of the mixing matrix. It presents the first systematic analytical model of external torques under ground effect, explicitly characterizing airflow-induced modifications to drag and the mixing matrix, while implicitly preserving system differential flatness via equivalent center-of-mass and inertia adjustments. A composite control strategy is proposed, integrating dynamics inversion with disturbance feedforward compensation to enable real-time, full-altitude ground-effect compensation. Experimental validation using force-measurement platforms and real-flight data demonstrates that the method reduces position control RMSE by 45.3%, significantly enhancing positioning accuracy and flight stability in close proximity to the ground.

Technology Category

• Intelligent Robots: State Estimation
• Search and Optimization: Mixed Discrete/Continuous Search
• Computer Vision: Low Level & Physics-based Vision

Application Category

• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs
• Responsible Web: Machine-in-the-loop, human agency and autonomy
• User Modeling, Personalization and Recommendation: Attacks and countermeasures in recommendation systems

Abstract

The ground effect on multicopters introduces several challenges, such as control errors caused by additional lift, oscillations that may occur during near-ground flight due to external torques, and the influence of ground airflow on models such as the rotor drag and the mixing matrix. This article collects and analyzes the dynamics data of near-ground multicopter flight through various methods, including force measurement platforms and real-world flights. For the first time, we summarize the mathematical model of the external torque of multicopters under ground effect. The influence of ground airflow on rotor drag and the mixing matrix is also verified through adequate experimentation and analysis. Through simplification and derivation, the differential flatness of the multicopter's dynamic model under ground effect is confirmed. To mitigate the influence of these disturbance models on control, we propose a control method that combines dynamic inverse and disturbance models, ensuring consistent control effectiveness at both high and low altitudes. In this method, the additional thrust and variations in rotor drag under ground effect are both considered and compensated through feedforward models. The leveling torque of ground effect can be equivalently represented as variations in the center of gravity and the moment of inertia. In this way, the leveling torque does not explicitly appear in the dynamic model. The final experimental results show that the method proposed in this paper reduces the control error (RMSE) by extbf{45.3%}. Please check the supplementary material at: https://github.com/ZJU-FAST-Lab/Ground-effect-controller.

Problem

• Modeling ground effect on multicopters' lift and torque
• Analyzing ground airflow impact on rotor drag models
• Developing control method to reduce ground effect errors

Innovation

• Dynamic inverse and disturbance model combination
• Feedforward compensation for ground effect forces
• Equivalent representation of leveling torque effects