Humanoid actuator sizing tool
Calculate actuator W/kg and estimate conversion heat at your operating point.
Published September 25, 2026 · Evidence reviewed October 11, 2026.
The calculator uses mechanical output power at the chosen rating point. For a rotating shaft, derive that power from torque and angular speed; then divide by the mass of the assembly you chose.
Manufacturer and research disclosures reviewed 11 October 2026. These are source-reported figures, not independent tests.
| Disclosure | Published metric | Valid use and limitation |
|---|---|---|
| Unitree H1 / M107 | 360 N·m maximum torque; 1.9 kg motor mass; 189 N·m/kg torque-to-mass ratio. | This is torque density, not power density. A torque-speed operating point and a matching assembly mass are needed to calculate W/kg. |
| Boston Dynamics Atlas | The product page lists 50 kg instantaneous and 30 kg sustained weight capacity. | Payload capacity is not actuator output power. The public product page does not give actuator mass-specific power. |
| QDD hip exoskeleton study | Reports a 3.4 kg bilateral exoskeleton design and evaluates its task-specific system. | A wearable device’s total mass and test conditions are not interchangeable with a humanoid joint actuator rating. |
The public figures above do not support a universal ranking of humanoid actuators by W/kg. In particular, torque per mass cannot be relabeled as power per mass, and a robot payload rating cannot be used as actuator output power.
| Risk | Why it changes the result | Next check |
|---|---|---|
| Mass boundary mismatch | A bare motor and an installed joint assembly have different denominators. | Record whether gearbox, inverter, cooling, housing, and mounts are included. |
| Peak rating overreach | A short burst does not establish repeatable or continuous output. | Record peak duration, repetition rate, voltage, speed, and temperature limit. |
| Thermal margin assumption | Estimated conversion loss alone does not reveal component temperature. | Measure temperatures through the intended duty cycle and cooling setup. |
Before selecting an actuator, request its torque-speed curve and continuous/peak rating conditions. Then calculate with the installed joint mass and verify temperature under the robot’s expected motion profile.
For the broader architecture and sourcing sequence, read the humanoid actuator procurement guide. To review available module families, see the humanoid robot actuator catalog.
Divide mechanical output power in watts by the declared actuator assembly mass in kilograms. For a rotating shaft, power is torque multiplied by angular speed; torque alone is not enough.
No. The same torque can produce different power at different shaft speeds. You need torque and speed measured at the same operating point, plus a clearly defined mass boundary.
Peak ratings are limited by short-term electrical, magnetic, mechanical, and thermal constraints. Continuous ratings also depend on heat rejection and temperature limits. Compare the stated duration, duty cycle, voltage, cooling, and ambient conditions before using either rating.
No. The displayed starting value is only an editable example. Replace it with measured efficiency for the operating point and stages included in your system boundary.
No. It estimates conversion loss from the selected efficiency; it does not model winding, magnet, bearing, or housing temperature. Validate the intended duty cycle with a thermal model or measurement.
Ask for a torque-speed curve, continuous and peak rating conditions, peak duration, efficiency map, thermal limits, and mass breakdown for the installed assembly.
Update the example with measured output, assembly mass, and efficiency, then use the result as a screening estimate.
