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Optical Shaft Encoder

An optical shaft encoder, or quadrature shaft encoder is a digital sensor that tracks the relative position and rotational distance of an axle. This is measured by an infrared light shining on the edge of a small disk that has evenly spaced slits at its edge. The encoder then measures the amount of times light has passed through the slits to determine how much has the axle has rotated and in turn, its relative position.1) Shaft encoders are frequently attached to the axles of drive systems and sometimes the output axles of lifts to measure the amount of rotations each respective system has done.

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Optical shaft encoders are some of the most widely used sensors in VRC due to its durability and reliability. They are seen attached to free-rotating mechanisms or any mechanism that require the tracking of relative angular position. Some ways shaft encoders are used include tracking the amount of times the wheels in a drive chassis have rotated, tracking the speed of a flywheel launcher and sometimes tracking the angle of a lift.


It is strongly recommended to take the installation of shaft encoders into account ahead of time as quadrature shaft encoders are the bulkiest sensors in VRC and take up a large amount of space in the robot. Shaft encoders use the axle attached to the rotating mechanism, or the output axle to rotate a black shaft at the center of the sensor. The housing itself is secured to the axle supports. Because of the sensor’s large size, many teams allocate space for it by adding a secondary output axle in a different area with an identical size gear or sprocket as the original output gear.

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vex_robotics_platforms/vex_edr/sensors/optical_shaft_encoder.txt · Last modified: 2017/11/13 05:23 (external edit)