[DonRotolo]

An encoder (in FRC parlance) is a sensor that detects rotation. The sensor technology can be resistive (potentiometer), optical, or magnetic (Hall sensor) to name a few.

Most encoders in FRC deliver pulses, so many pulses per revolution (except potentiometers). Using two carefully-placed sensors can deliver both speed and direction information.

The choice of the sensor technology to use depends on the application: Optical sensors can operate far faster, Hall sensors are great in sensing things magnetic, meaning your sensor wheel can be an existing gear or sprocket. In most cases, size/weight/cost/performance are the general tradeoffs.

The word Encoder has many definitions; here we are referring specifically to a rotational encoder.