direct drive
Direct drive means bolting the motor straight onto the thing it moves, with no gears, belts, or pulleys in between. Most robots place a gearbox between the motor and the joint to trade speed for strength, the way a bicycle's low gear lets you climb a hill. Direct drive throws that middleman away: the motor's own shaft is the joint, so whatever the motor does, the load feels instantly and exactly.
Skipping the gears buys three things that gears tend to spoil. There is no backlash — the tiny slack or wobble between gear teeth that makes a geared joint feel loose when it changes direction. The connection has high bandwidth, meaning it can react and reverse extremely fast and smoothly, because nothing springy or sloppy sits in the path. And it is backdrivable: you can grab the arm and push it by hand, and the motor turns easily, so the robot can feel outside forces instead of fighting them — which makes it gentle and safe to work alongside.
The catch is that a direct-drive motor has to be large and produce high torque on its own, because it gets no torque multiplication from gears. So you find direct drive where smoothness, speed, and a delicate sense of touch matter more than raw lifting power: high-end record-player turntables, camera gimbals, force-sensitive robot arms, and the agile legs of some walking robots.
Because a direct-drive arm has no backlash and is backdrivable, a person can nudge it aside by hand and it will softly comply instead of resisting — a key reason such arms are trusted to work close to people.
No gears in the way means the motor and the world can feel each other directly.
Direct drive is the opposite trade-off from a geared joint: it gives up cheap strength to gain speed, smoothness, and the ability to feel and yield to outside forces.