PCM Issues

Okay, so we’ve got green status lights. Until we enable and the compressor doesn’t run. The light switches to flashing green twice and then red and it cycles through that. It’s almost like it’s trying to run but can’t draw enough current? Has anyone this problem before? Any ideas?

1 Like

I did a quick search and couldn’t find anything quite like that. In case you haven’t already checked it out here is the PCM users guide. Section 3 (Pages 12-15) has the LED guide.

1 Like

Is your radio close to your PCM? (6-12 inches)

It’s over 12 but just barely. Why?

Check out the user manual, pages 14-16:

Try removing the compressor and any solenoids that are attached, see if it still faults. Then plug things back in one at a time, see where it starts faulting. That’ll be the easiest way to find the issue!

The PCM and the radio can interfere with each other if they are close but you have it about 12 inches away so it should be good.

Maybe the PCM can interfere with the radio’s signal, but the radio certainly won’t interfere with the PCM.

If you can’t find your answer in the User Guide, I would suggest calling or emailing CTRE. FRC suppliers like to help teams solve problems with their products, and they should definitely know what the status LED patterns mean.

I would have believed you two weeks ago. We spent nearly 5 hours debugging an issue that turned out to be the radio causing a “Compressor Fault”. During that time we swapped everything, PCM, compressor, pressure switch, solenoid and wiring. It was infuriating because our hands near the wires would imitate a loose wire. Finally our lead electronics mentor (thanks Katie) found a thread here on Chief Delphi of a similar problem.

Moved the radio, problem went away (they were adjacent on our practice bot).

Best guess the current sensing circuit that identifies the compressor fault (short) is susceptible to RF interference and the radio can be that source. Truthfully I don’t know, but I can demonstrate it 4 times out of 5 for you. Everything is working great, compressor running, touch the radio to the PCM and we get a compressor fault within 30 seconds.

EDIT: Just noticed you are in Israel, it is entirely possible you cannot replicate this problem if your radios are configured differently than the US.

We had a similar issue, I believe it had to do with plugging in the stranded wire. Once we switched to ferrule connectors, the problem went away. Therefore, you may not be getting a solid connection when plugging in the wires.

It is very easy to short circuit the compressor wires if you are not careful, because the strands don’t all like to go into the hole in the PCM. The wires are really too large for the connector, but we are required to use that size. Make sure there are no loose wire strands where the compressor connects.

Also, whenever there is strange robot behavior, I always ask the charge status of the robot battery.

Really…color me surprised. I also did wiring for the robot on my team in HS in the US for 4 years and I never even heard of that problem. I’m a bit skeptical, but I guess in theory that could be possible. I’d be interested in seeing a real controlled study as to whether this is a real effect or just a coincidence, and what actually causes the problem. No matter what, I’m pretty confident in saying that’s not the problem in this case.

I can confirm this. We ran into this problem last year and it had us stumped for HOURS. we finally ended up figuring out that it was the radio-PCM proximity when we bypassed the radio and started testing with USB. as soon as we reintroduced the radio to the system the PCM threw a fault again. We found our affected radius was about 6 inches but without fail when ever the radio was within 6 inches of the PCM it would shut down. it behaved literally like a light switch as soon as you are in the affected radius.

When you think about it, the radio is generating EMF so our PCM and our Radio now live on opposite sides of the robot. haven’t had an issue since. i will try and get a video tonight of the behavior.

I guess we got lucky!

This year our robot is large (27.98" wide by our best measurement), and most of the mechanisms are higher up on the robot. So we decided to put the electronics on a board at one end of the robot, down low. We then decided that we had enough area to put the pneumatics on a relatively large board, at the other end of the bottom of the robot. The PCM was on the electronics board, close to the radio. When we finally got the pneumatics installed, it was time to wire the ten solenoid valve wires, the pressure switch wires, and the compressor wires to the PCM. It looked daunting, because most of those wires were too short to reach the PCM. I finally realized…hey, the PCM runs on CAN, and it only needs power and CAN wires to it, and we can put it right by all the things it needs to connect to, and the wires will be short! except the CAN will have to take a slight detour on it’s way up to the top of the robot, and the PCM power wire will be a bit longer. So, we relocated the PCM to the pneumatics board, away from the radio, and the wiring was pretty easy and quick (aside from those pesky compressor wires). We never did have the opportunity for our radio to interfere with our PCM.

tldr; move the PCM away from the electronics, put it by the pneumatics.

Want to confirm that placing the radio next to the PCM is a bad idea. It consistently created compressor faults and the issue was resolved once moved away.

It would be best to check that all your wiring is actually good, as Mr. Forbes suggests.

I have seen the effects the OP is describing when working at EMC test labs but the RF power levels were much higher and with directional antennas that focus the RF energy into a narrow beam. On the off chance that this is a real EMC issue, have any of you who have experienced this issue contacted CTRE? They would have the insights regarding the internal circuitry of the PCM needed to properly understand the problem.

This issue was encountered while CSA at Heartland. There were 3 of us CSA’s looking over 1730’s wiring (already very clean I might add) until I randomly found this thread and suggested we move the radio and “magically” everything worked.

I just messaged a contact at CTRE we will see what they say

The PCM may appear to be a well-shielded board, but looks can be deceiving. We were having very similar issues earlier in the Build Season, until we took off the case for the PCM to find hundreds of metal shavings. We cleaned them out, removed them from the board, and the thing worked good as new. I highly recommend doing the same.