4:1
Two 2:1 stages per hip, using 16- and 32-tooth 5GT pulleys.
Orbit the integrated humanoid
whole-body STEP · hip-drive STEP · URDF · MJCF.
What is physically defined
50.91 mm
Both 225 mm belts close at the same solved pitch-center distance.
4 axes
Left/right hip pitch and roll share one mirrored serviceable architecture.
0
nominal common-volume conflicts among the four new rigid drive packages.
Mass and model boundary
The four candidate drive packages screen at 2.696 kg including four published 0.165 kg actuator masses. Replacing the prior hip actuator/pulley/belt allocation projects the active tether configuration to 11.705 kg—1.705 kg above the program maximum. That is a design blocker, not hidden contingency. This is a geometry-density estimate, not received mass. The derived URDF records 4.0 mechanical reduction and the MJCF carries the already executed inverse-feedforward successor scenario. Bearings, shaft material, belt tension/capacity, fasteners, stiffness, efficiency, reflected inertia, heat, guards, cables, motion sweep and physical proof remain open.