Direct-Drive Motors: The Rare, Expensive Alternative

Skipping the gearbox entirely solves backlash and backdrivability at once — for a price most designs can't justify.

A direct-drive actuator connects the motor directly to the joint with no gearbox at all, which eliminates backlash and gearbox friction entirely and makes the joint perfectly backdrivable, since there's no reduction stage to fight.

Why it's rare

Without gearing to multiply torque, a direct-drive motor needs to be physically large and heavy to produce useful torque at low speed — often impractically so for a human-scale limb — which is why direct drive shows up more in some robotic arms and research platforms than in commercial humanoid legs.

Where it does show up

Some high-end research manipulators and select joints on certain platforms use direct drive specifically where backdrivability and zero backlash are worth the mass and cost penalty — precise, compliant manipulation tasks being the clearest example.