AI & Humanoid Robotics Weekly

Actuators & joint modules

Integrated 'muscles' (motor + gearbox/screw + encoder + driver) that move each joint.

Data updated

Why it matters

A humanoid has roughly 28-40+ actuated joints. Rotary actuators (motor plus harmonic or planetary reducer) drive hips, shoulders and elbows; linear actuators (motor plus planetary roller screw) are used by Tesla and others in legs and forearms. Each module combines a frameless motor, reducer or screw, one or two encoders, often a torque sensor, bearings and a motor driver.

Why it is a bottleneck. Actuators are the largest cost block. Schaeffler puts them at ~50% of a humanoid's bill of materials and Hyundai Mobis at ~60% of material cost. Torque density, back-drivability, heat and lifetime are hard to achieve at low cost, and most volume capacity sits in China. Western makers face a sourcing trade-off between building in-house and buying from Chinese tier-1s.

Cost. BofA's projected 2030 humanoid BOM: linear actuators 27% + rotary actuators 24% = 51%. BofA put a China-built humanoid BOM at ~$35,000 in 2025.

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