REV PDH Fried at Comp

Technical Electrical
1

So…

At competition our New Rev PDH kinda “blew up.”

Context: We’ve been having issues all season with comms, etc. Later in the build season we shorted one connection by accident and popped the fuse. No big deal, just replace it, that’s what it’s meant for right? But then we had a hardware error (CSA Fault) which Rev assured us was okay to operate on. All that does is report current to the client, and they said the PDH would operate normally, so we went to competition.

Throughout competition we had issues. Especially towards the playoff matches there were constant brownouts and loss of communication from the constant resets mid match. Our robot was performing terribly and we couldn’t find the source of the issue, until we could smell the burning.

right before our, to be, final match the FTA’s, LRI’s, CSA’s were no the field trying to see what was up with our robot because it reeked of burnt something. They couldnt find anything so they let the match go on. After we lost our tiebreaker (partially because for the majority of the match we were just sitting unable to move), we started sniffing around to find that the positive main battery wire was “welded” to the terminal and burnt into it on the PDH. We’re going to hop on a call with Rev later this week/earlier next week but right now we’re putting all the OEM CTRE parts back on and getting our robot operational again.

My question - could the one short have contributed to this slow decline to everything going wrong (mod note: edited for profanity)? Has anyone else had issues with the new PDH like constant sticky faults, etc? I just want to know where we could’ve gone wrong?

Thanks

4573

2

Regardless of the root cause, it doesn’t feel good to be plagued with issues for an entire event. I have been there myself, and it really stinks. It is important in this time go through the troubleshooting process very systematically, now that you don’t have the pressure of matches looming down on you.

Reach out to us at [email protected] as soon as possible with photos before replacing components and rewiring the robot. It is essential to take photos of everything in its place as it was at competition, in extreme detail, so we have the best chance at finding the issue. It will be hard to diagnose without being in the shop with you, but we will do our best.

I suspect there was a major wiring problem on your robot. Maybe a loose connection, momentary short circuit, crossed wires, failed piece of electronics, or some combination of any of those. The wear and tear on the robot, especially during the quick-turn playoff matches could have made the root cause worse.

A few questions to get started, that we will also ask when you reach out to our support team:

  • It sounds like the field crew did not turn your robot off even though there was a burning smell, is that correct?
  • Was main battery wire hot when you got off the field, or could that damage have been from a previous match?
  • What wire gauge is your main battery wire leading into the PDH?
  • In any of your matches, did your main circuit breaker ever trip?
  • Is the main circuit breaker still functional, are you able to turn it off with the button?

The CSA fault you have seen means the internal controller on the PDH cannot talk to one or more of the Current Sense Amplifiers. A failure of a CSA chip will not affect the flow of power through the PDH. Even if there was an unlikely short circuit with one of these chips, the short would likely destroy the chip before it would overload the battery wire like you described.

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I’ll try and answer as much as I can remotely since I’m not at the shop right now but -

Reach out to us at [email protected] as soon as possible with photos

We did send an email out the friday of the competition (subject line 4573-electrical issue) with some pictures of the main pdh as well. Due to time constraints and availability we havent had the time to call and have a conversation over the phone yet

Unfortunately it seems they’ve already taken it apart, but multiple students and mentors saw no issues anywhere and neither did the inspectors, etc at the event… all the wire gauges and breakers were standard and normal as in the manuals

  • It sounds like the field crew did not turn your robot off even though there was a burning smell, is that correct?

Yep. It was QF4 Match 3 at FMA Mount Olive (1:23 is where we had the longest comms loss, likely because of another brownout)

right before that match started a group of officials were standing over our robot trying to find out why it was smelling burnt/not connecting to comms. They couldn’t find any issue and eventually the robot did connect so they let the match go on anyway.

The battery wires were not hot, and we even swapped another battery right before the match started (a second time on the FTA’s etc, insistance because of the brownouts they were seeing on their end)

Our battery wires were the standard 6awg wire

The main breaker never tripped (RSL would remain solid through all the DCs from the DS during matches), no individual breakers ever tripped either

The main breaker is still fully functional yes

After each match we double checked all connections since the new PDH/PCM would always come loose but nothing seemed out of place when we checked

all our motor controllers (the only thing on the robot really) are still functioning just fine with no faults so I assume that had nothing to do with it.

Hope some of this sheds some light on the subject and maybe you can find something. I’ll be sure to attach pictures of the charred PDH port via email within the next day or two

Thank you!!

4

It seems you had many knowledgeable people checking this out, so one of you all would have probably caught this if this were the case, but I have a small potential hypothesis as to how this could happen.

We switched to silicone battery cables, but they were a very large 6AWG. We had difficulty getting all the strands cleanly into the ports. The first few times, there were a few strands of cable that could have bridged the input ports on the PDH.

We figured it out, but I feel if that were the case, it could potentially create this problem. I am not shure if the main breaker would trigger in time in that event, but I am also not sure ut would be this intermittent either.

These are totally guesses mind you.

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