what is an actuator in robotics?

An actuator is the robot's muscle: the component that converts energy (almost always electricity) into physical movement. Every joint that turns, every gripper that grabs and every wheel that pushes has an actuator behind it, usually an electric motor with its gearbox, electronics and sensors integrated into a single block. If the sensor is the robot's eye and the software its brain, the actuator is the only thing that touches the world.

It is also the part that sets the price. A humanoid has 20 to 40 joints and each needs its own actuator: multiply and you understand why a humanoid robot used to cost hundreds of thousands of euros. The quiet revolution of the past decade was making them cheap: in-house motor designs and simple gear trains instead of catalog industrial components. That is how Unitree put its G1 at $16,000 and its R1 at $5,900, and it explains much of the Chinese advantage we tell in the night China took its robots dancing.

Actuators also define what the robot can do safely. A cobot's are deliberately weak and backdrivable, so a collision with a human ends in an apology rather than an injury. An industrial welding arm's are the opposite: power and stiffness inside a cage. And a surgical robot's like the da Vinci's trade force for sub-millimeter precision. Same concept, three philosophies.

Reading a spec sheet takes two questions: how many actuators it has (its degrees of freedom, meaning its dexterity) and how much torque they deliver (its useful strength). A spectacular video with mediocre actuators usually hides teleoperation or editing: muscle cannot be faked. That is why this house's spec pages list joints and payload next to the verdict.