Upgrading a Humanoid Leg Without Replacing Actuators: Torque–Speed Limits and Bench Measurements

Humanoid redesign with existing actuators requires balancing torque gain against loaded joint speed and holding duration. This study applies quasi-static load and torque–speed models to three generations of a 134 cm humanoid and measures the deployed hip-roll configuration on a separate bench. Stance narrowing and per-axis gearing increase the calculated hip-roll capacity ratio from 0.70 to 2.03, although the final configuration exceeds its target by only 1.4%. The bench uses two actuators and a 24:55 external gear pair to measure maximum speed at four loads and static holding at three loads. The speed measurements calibrate a torque–speed characteristic used to evaluate candidate reduction ratios. At approximately twice the reference moment, the measured speed is 47.8% below the no-load upper bound. At 23.39 N·m, holding trials terminate after 333–394 s at a prespecified reported-temperature criterion of 70 °C; both lighter loads complete 600 s. Unequal currents and temperatures indicate asymmetric actuator operation during holds. These results relate nominal torque margins to loaded speed and holding time, providing experimentally informed design checks without establishing performance during dynamic play.