Components of Robots.

ACTUATORS.
The 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, some of which are powered by electricity, while others use chemicals, or compressed air.

Motors:

By far the vast majority of robots use electric motors, of which there are several kinds. DC motors, which are familiar to many people, spin rapidly when an electric current is passed through them. They will spin backwards if the current is made to flow in the other direction.

Stepper Motors:

As the name suggests, stepper motors do not spin freely like DC motors, they rotate in steps of a few degrees at a time, 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 machining centres.

Piezo Motors:

A recent alternative to DC motors are piezo motors, also known as ultrasonic motors. These work on a fundamentally different principle, whereby tiny piezoceramic legs, vibrating many thousands of times per second, walk the motor round in a circle or a straight line. The advantages of these motors are incredible nanometre resolution, speed and available force for their size. These motors are already available commercially, and being used on some robots.

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 behaviour 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. For example, the Shadow robot hand uses 40 air muscles to power its 24 joints.

Electroactive Polymers:

These are a class of plastics which change shape in response to electrical stimulation. They can be designed so that they bend, stretch or contract, but so far there are no EAPs suitable for commercial robots, as they tend to have low efficiency or are not robust. Indeed, all of the entrants in a recent competition to build EAP powered arm wrestling robots, were beaten by a 17 year old girl. However, they are expected to improve in the future, where they may be useful for microrobotic applications.