TRACER: Thrust Auto-calibration and Ground Effect Estimation Using Onboard Force Sensitive Resistor Array for Multirotors

Abstract

Auto-calibration of the rotor thrust coefficient and estimation of ground effect are both challenging aspects of multirotor dynamics control and planning. Conventional approaches address these issues separately and typically rely on experimental rigs for bench testing. In this paper, we propose a low-cost onboard sensor array and a well-designed unified algorithm to enable fast auto-calibration of the rotor thrust coefficient alongside ground effect estimation (TRACER). Our sensor array consists of four force-sensitive resistors compactly placed under the quadrotor landing gear to measure contact force during the lift-off phase, capturing changes in thrust. The joint calibration and estimation problem is formulated to rapidly decouple ground effect influence from free-air rotor thrust based on sensor readings. Furthermore, our approach is adaptable to various flight control input formats (duty cycle, rotor throttle, or rpm), ensuring general applicability across different multirotor operations. Experimental results demonstrate that the proposed method provides reliable joint calibration and estimation of rotor thrust and ground effect in a short lift-off process, achieving less than 10% mean absolute percentage error compared to the ground truth.