Using CIMCoders with Talon SRXs

Technical Electrical
1

When wiring CIMCoders to talons using breakout boards we’ve been getting inconsistent readings. Moving the drivetrain one direction makes the encoder values increase significantly more than moving it the same distance in the other direction (factor of 4 to 10). We don’t have this issue when plugging into the RoboRio directly. A spare grayhill we had also worked fine.

We tried adding 10K ohm pull up resistors which seemed to work for a little while before we began to get inconsistent values again.

Has anyone else had this issue before and are pull up resistors the proper solution?

2

I do believe a pull up resistor is needed, but I think you aren’t using the correct resistance. See the graph here: http://www.robotshop.com/media/files/pdf/CIMcoder_Spec_Sheet_1-27-16.pdf. You need a different resistance depending on whether you are using 5v or 3.3v with the talon.

3

Are your readings only inconsistent while running the robot?

4

Readings are inconsistent whether the wheels are hand spun or driven by the motors. We don’t think it’s a gearbox engagement issue or anything similar.

5

Seeing the Cimcoder is a 5V sensor we used a 4.7K Ohm resistor to Vdd.

If I remember right it was 10k at 12v, but the srx is 5v/3.3v.

We used the CTE breakout for these.

Added- the encoder is 20 cpr, the srx is 4x decode the signal, so you should see 80 native counts per rev in the srx webpage. going from Memory