Combination of Quadrature and Absolute Encoder

General discussion of using Roboclaw motor controllers
citrusying
Posts: 4
Joined: Wed Jul 18, 2018 10:50 am

Combination of Quadrature and Absolute Encoder

Postby citrusying » Wed Jul 25, 2018 3:49 am

Hi

I am using 2 DC motors with quadrature encoders (Motor 1 and 2) with a RoboClaw 2x30A. Unfortunately Motor 2has a suspected faulty encoder such that the encoder counts do not increase with the motor shaft rotation.

To circumvent the issue, I would like to explore using a standard potentiometer as an absolute encoder for Motor 2 while keeping to the quadrature encoder for Motor 1. In that case, I would use the wiring diagram for quadrature encoder wiring for Motor 1 and absolute encoder wiring for Motor 2. Will this be a problem for RoboClaw to function? For this potentiometer (https://uk.rs-online.com/web/p/potentiometers/1548183/), its max voltage is 5V, is it still necessary to include a resistor? If so, how should I determine the type of resistor to use since I would also be using 1 potentiometer instead of 2?

Thanks.

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Basicmicro Support
Posts: 1003
Joined: Thu Feb 26, 2015 9:45 pm

Re: Combination of Quadrature and Absolute Encoder

Postby Basicmicro Support » Wed Jul 25, 2018 9:04 am

Potnetiometers have a limited amount of turn. Some as little as 90 degrees. Some are multi turn but still a limited number of turns. If you application only uses that amount of range then there shouldnt be a problem. You can set one encoder to quadrature and the other to absolute(eg analog).

You do still need the resistor. The analog inputs on the Roboclaw have a range of 0 to 2v. The resistor is there so the pot will produce a full range(0 to 2v) approximately. If you dont use it the pot will use 0 to 5v and anything above 2v is simply clipped so you lose alot of range on your pot. In that 2v range roboclaw has 11bits of resolution(2048 descrete positions).


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