Ferrules falling out of PCM

We had a fun problem yesterday, fortunately on the practice field. We lost pneumatics. Discovered a power wire came out of the PCM. We used 18 gage wire, with crimp on ferrules. The spring loaded connector just won’t grip the ferrule properly. Cut off the ferrule, stipped the wire, inserted it in the connector, works great.

Anyone else had issues like this?

I’m pretty sure the ferrule is the correct size, proper crimping tool, etc.


We had the same problems. After fighting loose wires and issues with inserting the larger gauges that fit, I naturally jumped on the ferrule trend that is taking over FRC. We haven’t used a single one in competition because they just don’t stay put when doing a tug test. So now I have bags and bags of ferrule and a nice crimper that sit in a drawer in our shop. The weidmueller connectors seem to just like stranded wire better in our case (and apparently yours)


Does your crimper make square crimps with annular ridges/serrations? Do your ferrules have a ~10mm pin length?

This thread from earlier this season is a good one on this topic.

EDIT: They called us dumb when we spent all our FIRST Choice and PDV dollars on VRMs and PCMs, but we got brand-new weidmuellers out of it.

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We have a hex crimper, but yes it has serrations and yes the pins are the right length. It’s not that they wouldn’t insert, they just slip right out. With stranded wire I worry about breaking the wire before they release. The ferrule slides our with a depressingly low amount of effort.

we use a square shaped crimp. but size matters. if your Ferrule is too large it will either jam the connector open or not allow the metal tab that holds it in enough advantage keep it in.

I got the inventables kit this year. Only the pink ferrules work in the PCM. I don’t know the size, but every other ferrule failed to stay in. These ferrules were pretty small and for larger wire gauges (like to the compressor) I had to cut some strands off of the 18 awg wire so that it would go into the ferrule.

edit: I am very happy with how well these ones do stay in. I struggled at first to find a good size. I should try to find the actual size in the off-season, so I can buy more in a documented way. The crimper is the one inventables had and is circular with sort of a square crimp with serrations. Also, the student started out trying to crimp the entire ferrule with the insulation in there, and all of those connections were bad. For larger gauge, I would add a little heat shrink or tape to cover between the ferrule insulation and wire insulation, because the wire is too large to slip inside the ferrule insulation.

edit2: Apparently inventables is out of ferrules and crimpers, so I can’t suggest going to them. I’ll try to get some measurements and post here after a while.

Thanks for the replies. Looks like we have to do some more research. Our long time electronics mentor did not return this year, so I have had to pick up the slack, and I missed a few things!

The orange weidmuller ferules work with a square crimp and ridges. We get them in bulk for a lower price.

I will tell you one place we won’t use them - the roborio. The roborio power connection is just about the most problematic connection we have on the robot. I hate that thing.

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I’ve seen problems with retention with some square crimps using the common (cheap) tool. The two crimpers which work best in my experience is the one available on McMaster (P/N 5722K12) or the official Weidmuller PZ-6 Roto (which I’ve seen for ~$125 on eBay from Germany), both of which produce a trapezoidal crimp. They are also the only ones I’ve found which will crimp the 16AWG wire of the compressor such that it will fit.

I agree ferrules don’t seem to work well on the Rio power plug, but they are handy wiring your signal light.

We were originally using ferrules on all of our electrical connections besides CAN, the 40A and 30A PDP slots, and RIO power. We eventually removed them all because they were vibrating out of the weidmuller connectors. I suspect that the plastic casings around the back end of the ferrules were pushing against their neighbors and wiggling eachother out. As long as the ferrules stayed in place, the connections were fine.

I’m pretty sure that part of our problem was that our compressor was mounted to our poly-carbonate belly pan, along with all of the other electronics. Everything vibrated a lot while the compressor was running and the ferrules didn’t seem to like that. all of the connections stayed put once we removed the ferrules and inserted bare wire into the connectors.

The following is a bit off topic and I’ll remove this if it’s deemed inappropriate for the thread but we received a ton of questions about it so I figured I would get ahead of the curve here. In case anyone is wondering, the poly-carbonate worked okayish and I wouldn’t really recommend it over aluminum. It was very lightweight and fast to machine, and it was easy to spot loose bolts or tools. Wiring was also alright because we could clearly see everything. On the less bright side, it vibrated significantly more than I expect an aluminum substitute would. It made it all the way through 23 matches of aggressive defense and driving. About half of those were started on level 2. In our very last match something failed and the front end of the belly pan came loose from the robot. I didn’t get a chance to inspect what caused the failure. The polycarb itself could’ve cracked along the bolt holes, or the bolts themselves could’ve stripped out of their holes. As far as I know we had no issues with static discharge. I think it was a neat idea and we might use it again for test beds and demo bots, but probably not on a competition robot - certainly not for a game as physical as Deep Space.


We have our compressor mounted to our (kit) chassis, and the electronics mostly mounted to a piece of polycarbonate that is also attached to the chassis. I don’t think we have any vibration issues, but I haven’t really investigated that.

When we get to Champs, we’ll take another look at all the connections…

I saw the same thing with one of the teams at Bayou this weekend. IIRC, it was during lunch break on Friday with team 3468. I verified that their crimper made square blocks, but when those wouldn’t hold, they resorted to cutting and stripping, and had no further issues. The FRC connectors (WAGO and Weidmuller) certainly seem to be designed for stranded wire, not solid ferrules.


I have used ferrules on all power connections to the PDB from the time it was blue. I have never had one wiggle out. what you are describing should never happen :frowning:

We used no ferrules on the main PDP slots - only the weidmuller connectors on the VRM, PCM, and power ports on the end of the PDP for the RIO, VRM, and PCM. My post was a bit confusing on that. We talked to several other teams using ferrules at both of our events. Some absolutely loved them, and some had the exact issues we did. There was a mile long list of problems with the electrical system on that robot, so it’s entirely possible that the issue was coming from somewhere else and the ferrules were a symptom and not the issue itself. However, removing the ferrules did seem to help. For now we’re choosing to stick to bare wire in the connectors.

When the NI system came out, I had an old NASA technician as a mentor. He looked at us trying to fit stranded wire into the PDB and seeing strands sticking out and causing shorts. He took one look at connection told us they used similar connections all the time with NASA. He explained to us that these connections are designed to use ferrules. He fulled out an old zipped canvas bag with 100’s , if not thousands, of connectors and the square crimper. It solved problem and we’ve never looked back since. interesting. Sounds like I need to do some research.

We definitely do as well! We’re always careful to ensure every wire strand ends up inside. Every time a wire is inserted we do a 360 inspection with a flashlight. As far as I know we haven’t had any shorts specifically from loose strands. I only began learning about the FRC electrical system this year and our primary electronics person is also pretty new to it so I don’t mean to sound like I know better than you! I just meant to express my team’s experiences with ferrules this year. This was our first year using them and there were several other issues like I said so it’s possible and likely that we were the issue, not the ferrules.

If should was wood, house’s 'd be cheap.

Seriously, though, the only times I’ve seen stranded wires come out of the WAGOs or Weidmullers was when they were cut incorrectly, or the wrong gauge, or just shoved in. Cut the end square, cut the right amount of insulation off, don’t damage or taper the strands, do a VERY slight twist to keep the strands together, open the connector with an appropriate tool, insert the wire, release the tool, tug test.

As far as I’m concerned, the bottom line is that it’s just as easy to mess up a crimp job as a manufacturer’s recommendation job - and apparently* harder to notice on inspection that you have a problem.

* Qualified as I have done far fewer ferrule inspections than recommended inspections. In recent years, I have learned to trust PROPER crimps as much as good-flow solder joints, but I have still encountered several bad crimp jobs involving blind-end wire inserts which appeared good on inspection, but which later failed due to too little insulation being stripped, tapered ends, or nicked strands.

We buy all of ours from CTRE. Figure you can’t go wrong.

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We too have had some issues with using ferrules for the vrm slots, one thing I can say is make sure that the wire goes ALL the way through the ferrule. If you crimp one without wire in it, it will not stay in the connector

We used the ferrules Spectrum bought from TE (http://blog.spectrum3847.org/2018/11/first-choice-and-kop-vouchers.html?m=1) and the AM ferrule crimper. They require a solid bit of a tug and grip to get out too. We haven’t had any issues except with compressor, we were unable to use ferrules on the 14 AWG that comes with it but I’m thinking we can connect 18AWG to compressor wires and use that.