B grade Authoritative secondary, traced to origin

Integrated joint motors: what replaced hobby servos, and what it costs you

A brushless motor, gearbox and driver squeezed into one cylinder and chained on a single bus — the direct reason a low-cost humanoid can hit a USD 2,500 price. It also raises the tooling barrier by one notch.

Construction: Brushless motor, gearbox and driver integrated
Communication: CAN FD bus, several joints on one line
Price band: About USD 110-225 per unit, by model and torque class
Typical use: The 12 actuated lower-body DOF of LeRobot Humanoid
Versus servos: Far more torque and thermal headroom; far more wiring and tuning complexity

The spec, and what it measures: These motors are rated at the joint level, not the bare motor level: peak torque, continuous torque, gear ratio, maximum joint speed, and the thermal conditions behind each. The most common comparison error is reading peak torque as continuous — peak holds only briefly, and continuous is the figure that survives a long run. Look for the word continuous first.
Price tiers: From just over a hundred to just over two hundred dollars per unit, so a 12-DOF humanoid spends close to two thousand on motors alone — about 70% of the machine. Dropping to servos is an order of magnitude cheaper but neither torque nor durability holds up at humanoid scale; moving up to industrial joint modules multiplies the unit price several times. This band is where low-cost humanoids currently land.
How to pick: (1) Specify by joint position: hip and knee need something entirely different from ankle, and mixing models saves real money. (2) Note what integration costs you: a built-in driver removes external drivers and cabling but also removes a layer you could swap out. (3) Size the bus load: several joints on one line means control frequency and data volume have to be planned together. (4) Leave thermal margin: heat build-up under continuous operation is the most consistently underestimated figure here.
Known pitfalls: (1) Treating peak torque as continuous, then watching the motor throttle itself back after a few minutes of running. (2) Lock-in from the integrated driver: parameters and protection logic live in vendor firmware, leaving little room when something misbehaves. (3) Bringing servo debugging habits along: tuning, zeroing and protection thresholds are all in a different toolchain and have to be learned again.
What we checked: We checked the communication method (CAN FD) and integrated construction, the specific models and their distribution across joints on LeRobot Humanoid, and the price bands. Not checked: we have not run torque-bench or thermal tests, so how much continuous torque survives in a real thermal environment is not measured here.

This site's call

If your joints need sustained torque and you are synchronising a dozen of them, integrated motors are the least painful option — you spend money to remove external drivers, wiring and a custom joint design. At desktop-arm scale, servos remain the better deal and are far friendlier to debug. The dividing line is whether continuous torque is sufficient, not the number of degrees of freedom.

Peak and continuous differ by more than a number

Peak torque is the force to turn something once; continuous torque is the force you can apply indefinitely. Specify by the first and the bill arrives later as thermal throttling — and by then the machine is already built, which is the most expensive moment to change anything.

A judge that costs no time

Open the thermal section of the datasheet and find "continuous torque" with its test conditions. If ambient temperature and duration are stated, you can specify from the sheet. If there is only a peak figure, discount it by experience before deciding it is enough.

Sources

Vendor datasheets: peak torque, continuous torque and thermal conditions
Bills of materials and selection notes published by open humanoid projects (models mapped to joint positions)

Objects in this entry

Last checked 2026-09-28