Actuation

Actuators are the "muscles" of a robot, the parts which convert stored energy into movement. By far the most popular actuators are electric motors, but there are many others, powered by electricity, chemicals, and compressed air.

* Motors: The vast majority of robots use electric motors, including brushed and brushless DC motors.
* Stepper motors: As the name suggests, stepper motors do not spin freely like DC motors; they rotate in discrete steps, under the command of a controller. This makes them easier to control, as the controller knows exactly how far they have rotated, without having to use a sensor. Therefore, they are used on many robots and CNC machines.
* Piezo motors: A recent alternative to DC motors are piezo motors or ultrasonic motors. These work on a fundamentally different principle, whereby tiny piezoceramic elements, vibrating many thousands of times per second, cause linear or rotary motion. There are different mechanisms of operation; one type uses the vibration of the piezo elements to walk the motor in a circle or a straight line.[10] Another type uses the piezo elements to cause a nut to vibrate and drive a screw. The advantages of these motors are nanometer resolution, speed, and available force for their size.[11] These motors are already available commercially, and being used on some robots.[12][13]
* Air muscles: The air muscle is a simple yet powerful device for providing a pulling force. When inflated with compressed air, it contracts by up to 40% of its original length. The key to its behavior is the braiding visible around the outside, which forces the muscle to be either long and thin, or short and fat. Since it behaves in a very similar way to a biological muscle, it can be used to construct robots with a similar muscle/skeleton system to an animal.[14] For example, the Shadow robot hand uses 40 air muscles to power its 24 joints.