A potentiometer is a variable resistor that is typically used on a robot to measure shaft angle or number of turns of a shaft. The potentiometer has a resistance that is proportional to the angle of the shaft on the device. There are several styles of potentiometers available. The potentiometers used on robots should be linear taper (not logarithmic as used in audio equipment for volume controls).
Typically a potentiometer shaft can rotate about 270 degrees before hitting the hard stop. It is important to make sure that the mechanical system the potentiometer is connected to doesn't exceed the maximum rotation of the potentiometer or it will likely become damaged. For applications requiring more rotations, multi-turn potentiometers are available. Using a 10-turn potentiometer often simplifies the mechanical design of a system such as an elevator where the rotations translate into elevator height.