KOP Drivetrain with E4T/E4P

We have built a test drive-train using an AndyMark KOP frame, 4 CIM motors, and some US Digital E4P encoders.

We have discovered an issue that doesn’t make a whole lot of sense. The left side of the drive-train reads much higher than the right after driving it with just the joystick.

We believe this is a mechanical issue in either the gearbox or another friction point on the right side of the drive-train. However…

I put the drive-train on the wooden platform and did a reset of the encoders (and gyro) and manually turned each wheel as close to 360 degrees as I could and the left still reads about 10% higher than the right and one revolution gives only about 150 counts but the encoder is a 360. Have you seen anything like this?

I plan on setting the encoding to k1x in place of k4x to see if that has any effect on the encoder ticks. Maybe the FPGA is not getting all of the signals.

If you’re not scrupulously careful with the E4Ps, the encoder wheel can end up in contact with either the laser or the housing, which will make it slip on the shaft (and, if it’s the former, potentially scratch it up and render it damaged and useless). This can cause the symptom you’re seeing. You have to make absolutely sure it’s “free-floating.”

I don’t think this is your problem, but we had a very similar issue during the season and it turned out to be the Talon breakout board that we were using. We were using the new breakout boards from AM with the RS7 encoder and found that we would accumulate about a 10% error after 360 degrees of rotation. We believe the cause was a mismatch of pull up resistors between that board and the RS7 encoder.
To get around the problem we just used the older Talon SRX breakout boards and the problem disappeared. Unfortunately we never fully root-caused the issue, but that was our fix.

I’ve had similar problems created by a scratched disk. In my case, essentially one quarter of the turn only produced a few clicks, where the other three quarters produced the desired number. But you would have to have over half the disk obliterated to only get 150 clicks instead of 360.

Those encoders are useless. We spent all of 2017 fiddling with them and they never worked properly. We switched to S4T’s and have had no issues since.

It wouldn’t be the first time the wrong disc was provided, or installed, with one of those encoders. Or a disc being installed not-quite-square, or having the install tool damage the plastic encoder disc, or have a LOOSE plastic encoder disc… (the marks are printed on a thin plastic disc that is pressed onto the aluminum disc/hub part).

We stopped using them a few years ago, using only Grayhill 63R-256 encoders instead, and have been much happier.