The Optical Shaft encoder is used to measure both relative position of and rotational distance traveled by a shaft. It works by shining light onto the edge of a disk outfitted with evenly spaced slits around the circumference. As the disk spins, light passes through the slits and is blocked by the opaque spaces between the slits. The encoder then detects how many slits have had light shine through, and in which direction the disk is spinning.

The Optical Shaft Encoder can be used to improve a robot in various ways. The encoder can measure rotational distance traveled and speed, which can be used to monitor, for example, the angular position of a robot gripper arm or the speed of a robot. Knowing these parameters can greatly assist you with performing autonomous tasks with your robot.

With the Quadrature Encoder's two output channels you can measure both the position and direction of rotation of a VEX shaft. This will allow you to calculate the speed of the shaft, as well as the distance it has traveled using programming software. Encoders are typically used for “infinite rotation” applications, such as a drive wheel. A Programming Kit is needed to change the program in the VEX Controller to use the Quadrature Encoder.