The structure of a robot is usually mostly mechanical and is called a kinematic chain (its functionally similar to the skeleton of human body). The chain is formed of links (its bones), actuators (its muscles) and joints which can allow one or more degrees of freedom.
Some robots use open serial chains in which each link connects the one before to the one after it. Robots used as manipulators have an end effectors mounted on the last link. This end effectors can be anything from a welding device to a mechanical hand used to manipulate the environment.
Actuation is the “muscles” of a robot, the parts which convert stored energy into movement. The most popular actuators are electric motors.
The vast majority of robots use electric motors, including bushed and brushies DC motors.
3. Stepper motors:
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.
4. Piezo Motors:
A recent alternative to DC Motors are piezo motors or ultrasonic motors. Tiny piezoceramic elements, vibrating many thousands of times per second, cause linear or rotary motion.
5. Air Muscles:
The air muscle in a simple yet powerful device for providing a pulling force. 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.
6. Electroactive polymers:
Are classes of plastics which change shape in response to electric stimulation.
7. Elastic Nanotubes:
The absence of defects in nanotubes enables these filaments to deform elastically by several percent.
Robots work in the real world require some way to manipulate objects; pick up, modify, destroy or otherwise have an effect. Thus, the hands, of a robot are often referred to as end effectors. Most robots arms are replaceable effectors, each allowing them to perform some small range of tasks. Some have a fixed manipulator which cannot be replaced, while a few have one very general purpose manipulator.