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A Generalized Thrust Estimation and Control Approach for Multirotors Micro Aerial Vehicles

Davi Santos, Martin Saska, Tiago Nascimento

TL;DR

The paper tackles per-rotor thrust estimation and control for multirotor UAVs by leveraging a generalized Blade Element Momentum Theory (BEMT) framework to derive a closed-loop estimator and a feedforward-augmented thrust controller. By reducing the aerodynamic identification to a small set of parameters and solving constraint equations offline, the method enables practical, wide-ranging applicability across platforms with minimal calibration. Implemented in the PX4 stack and validated on 250 mm and 500 mm quads, the approach demonstrated superior robustness to wind and forward-flight disturbances compared with a traditional quadratic thrust-to-speed map, at the cost of modestly higher power consumption and computation. The results indicate meaningful improvements in thrust tracking and flight robustness in real outdoor conditions, with real-time onboard execution at 500 Hz and potential for broader adoption in diverse multicopters. Overall, the work contributes a generalized, transportable thrust estimation/control framework that enhances low-level rotor fidelity, thereby improving high-level flight robustness and control performance.

Abstract

This paper addresses the problem of thrust estimation and control for the rotors of small-sized multirotors Uncrewed Aerial Vehicles (UAVs). Accurate control of the thrust generated by each rotor during flight is one of the main challenges for robust control of quadrotors. The most common approach is to approximate the mapping of rotor speed to thrust with a simple quadratic model. This model is known to fail under non-hovering flight conditions, introducing errors into the control pipeline. One of the approaches to modeling the aerodynamics around the propellers is the Blade Element Momentum Theory (BEMT). Here, we propose a novel BEMT-based closed-loop thrust estimator and control to eliminate the laborious calibration step of finding several aerodynamic coefficients. We aim to reuse known values as a baseline and fit the thrust estimate to values closest to the real ones with a simple test bench experiment, resulting in a single scaling value. A feedforward PID thrust control was implemented for each rotor, and the methods were validated by outdoor experiments with two multirotor UAV platforms: 250mm and 500mm. A statistical analysis of the results showed that the thrust estimation and control provided better robustness under aerodynamically varying flight conditions compared to the quadratic model.

A Generalized Thrust Estimation and Control Approach for Multirotors Micro Aerial Vehicles

TL;DR

The paper tackles per-rotor thrust estimation and control for multirotor UAVs by leveraging a generalized Blade Element Momentum Theory (BEMT) framework to derive a closed-loop estimator and a feedforward-augmented thrust controller. By reducing the aerodynamic identification to a small set of parameters and solving constraint equations offline, the method enables practical, wide-ranging applicability across platforms with minimal calibration. Implemented in the PX4 stack and validated on 250 mm and 500 mm quads, the approach demonstrated superior robustness to wind and forward-flight disturbances compared with a traditional quadratic thrust-to-speed map, at the cost of modestly higher power consumption and computation. The results indicate meaningful improvements in thrust tracking and flight robustness in real outdoor conditions, with real-time onboard execution at 500 Hz and potential for broader adoption in diverse multicopters. Overall, the work contributes a generalized, transportable thrust estimation/control framework that enhances low-level rotor fidelity, thereby improving high-level flight robustness and control performance.

Abstract

This paper addresses the problem of thrust estimation and control for the rotors of small-sized multirotors Uncrewed Aerial Vehicles (UAVs). Accurate control of the thrust generated by each rotor during flight is one of the main challenges for robust control of quadrotors. The most common approach is to approximate the mapping of rotor speed to thrust with a simple quadratic model. This model is known to fail under non-hovering flight conditions, introducing errors into the control pipeline. One of the approaches to modeling the aerodynamics around the propellers is the Blade Element Momentum Theory (BEMT). Here, we propose a novel BEMT-based closed-loop thrust estimator and control to eliminate the laborious calibration step of finding several aerodynamic coefficients. We aim to reuse known values as a baseline and fit the thrust estimate to values closest to the real ones with a simple test bench experiment, resulting in a single scaling value. A feedforward PID thrust control was implemented for each rotor, and the methods were validated by outdoor experiments with two multirotor UAV platforms: 250mm and 500mm. A statistical analysis of the results showed that the thrust estimation and control provided better robustness under aerodynamically varying flight conditions compared to the quadratic model.

Paper Structure

This paper contains 8 sections, 14 equations, 10 figures, 3 tables, 1 algorithm.

Table of Contents

  1. Introduction
  2. Related work
  3. Aerodynamic power modeling
  4. A Generalized thrust estimation and control approach
  5. Generalizing the thrust estimation
  6. Thrust control
  7. Results
  8. Conclusion

Figures (10)

  • Figure 1: Quadrotors used in our experiments. The 500mm is on the left, and the 250mm is on the right.
  • Figure 2: Quadrotors body frame and rotor thrust.
  • Figure 3: PX4 control pipeline. We removed the red block and added the green blocks. The thrust control and estimator blocks run at 500Hz on a Pixhawk 6C.
  • Figure 4: Different forces, torques, and powers on a rotor.
  • Figure 5: Setup used for the thrust test bench experiment.
  • ...and 5 more figures