Wireless Center of Pressure Feedback System for Humanoid Robot Balance Control using ESP32-C3

TL;DR

This work presents a wireless CoP feedback system for humanoid balance using foot-mounted load cells and an ESP32-C3, enabling real-time CoP estimation and wireless control of a 29-DoF robot. A dual-PID strategy (Pitch for $COP_y$ and Roll for $COP_x$) governs torso, hip, and ankle roll to maintain balance on inclined or uneven surfaces, achieving robust performance with modest calibration errors. Key findings include average load-cell errors around $\sim$$15\ \mathrm{g}$ per foot and a $100\%$ balance success at a $3^{\circ}$ tilt with $K_p=0.10$ and $K_d=0.005$, validating the efficacy of wireless CoP feedback for postural stability. Practical impact includes reduced wiring complexity, improved dance-robot stability, and a path toward higher-performance actuators and ZMP-based balance strategies.

Abstract

Maintaining stability during the single-support phase is a fundamental challenge in humanoid robotics, particularly in dance robots that require complex maneuvers and high mechanical freedom. Traditional tethered sensor configurations often restrict joint movement and introduce mechanical noises. This study proposes a wireless embedded balance system designed to maintain stability on uneven surfaces. The system utilizes a custom-designed foot unit integrated with four load cells and an ESP32-C3 microcontroller to estimate the Center of Pressure (CoP) in real time. The CoP data were transmitted wirelessly to the main controller to minimize the wiring complexity of the 29-DoF VI-ROSE humanoid robot. A PID control strategy is implemented to adjust the torso, hip, and ankle roll joints based on CoP feedback. Experimental characterization demonstrated high sensor precision with an average measurement error of 14.8 g. Furthermore, the proposed control system achieved a 100% success rate in maintaining balance during single-leg lifting tasks at a 3-degree inclination with optimized PID parameters (Kp=0.10, Kd=0.005). These results validate the efficacy of wireless CoP feedback in enhancing the postural stability of humanoid robots, without compromising their mechanical flexibility.

Figures (10)

• Figure 1: Overall System Diagram
• Figure 2: Mechanical Design of the Robot and Servo ID Naming
• Figure 3: Electronic and Communication Diagram Between Components
• Figure 4: Overall Design of the Robot Foot
• Figure 5: Application Used for Load Cell Configuration