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Encoder

A project log for Jungle Vine Swing Robot

Controlling reeling in/out a rope

ekEK 11/09/2021 at 02:270 Comments

A quadrature encoder is an encoder that measures both speed and direction. It's quad (meaning 4) because there's two sensors that can give two values (1 or 0).

There are two square waveforms that are 90 degrees out of phase with each other. The direction is known depending on the order. The frequency is known depending on how many.


quadrature encoder A-B output channel diagram[source] Also more information available here

It is possible to increase the resolution of the encoder by detecting both the leading and trailing edges of the pulse. When done for both channels, it quadruples the resolution aka pulses per revolution.

Here are the alternative encoder methods, and the reason for choosing magnetic over them:

Encoder MethodReason for Not Choosing
OpticalEnd device would be deployed in a dusty environment where optical could be prone to errors
Magnet on drive shaftBacklash in gearbox of the device makes the movement from the drive gear different than the actual on the output gear
Field oriented controlDesign of this device should be portable to different configurations, whether that's stepper, brushed, brushless, or even no motor

Downsides to the magnet approach are the cost of the magnets and the size.

Next step for encoder work is determining the hall-effect sensors, magnets, placement of magnets.

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