Actuator

The part that converts electrical, hydraulic, or pneumatic energy into motion and force — a robot's “muscle.”

An actuator is the part of a robot that actually produces motion. By energy source, actuators are electric (motors), hydraulic, or pneumatic, plus newer types like shape-memory alloys and artificial muscles. Whatever command a controller computes — a target position, velocity, or torque — ultimately has to be carried out by an actuator, and its torque, speed, precision, weight, and heat output directly determine how fast, how heavy, and how finely the robot can move. Most humanoid and quadruped robots today use joint actuator modules built from a motor plus a gearbox; Boston Dynamics' early Atlas used hydraulics before switching to an all-electric version starting in 2024. Common specs for choosing an actuator include peak torque, torque density (torque per unit weight), and backdrivability (whether an outside force can push the joint back). Note: in Chinese, 驱动器 sometimes also means “actuator” (as in a series elastic actuator), but more often refers specifically to the motor-driver electronics that regulate current — the meaning depends on context.

ExampleIn April 2024, Boston Dynamics retired the hydraulic Atlas it had used for over a decade and replaced it with a new all-electric Atlas; the company said the new version is stronger and has a wider range of motion than any previous generation.

Related

Joint Actuator Module · Servo Motor · Speed Reducer / Gearbox · Hydraulic Actuation · Torque Density · Backdrivability

Sources

Actuator - Wikipedia
Boston Dynamics: An Electric New Era for Atlas (2024-04)