PWM cables: too fragile? what fixes/precautions?

Has anyone else (over the years, or lately) been having problems with PWM cables going/being bad?

I don’t think that my team is particularly hard on stuff (especially things that are ~$5 a piece) but each year we seem to run into problems with some the PWM cables working only intermittently, or just not working at all.

…and before I get the warnings… No, We do not do any of the following:

***** route them beside power wires
***** do things to/put them in places that would take off insulation
***** fold/crease the wires
***** use them as “structural” or “fastening” members, etc…

After 5 years of this same problem, I am guessing that this afflicts most other teams as well. What works to counteract this?

Any help would be greatly appreciated

We have PWM cables go bad from time to time. It happens, we suspect that for some reason the pins change size or lose their spring and just give high resistance. When in doubt, throw it out.

I agree with you there…it is just that it gets expensive!



Every year we have problems with seating our PWM cables, whether they are the ones supplied in the kit or ones we crimped ourselves.

This year, 5 out of 6 of our cables running to our Victors failed to work properly the first time we connected them. All 4 of 4 cables running to the Spikes worked fine however.

The difference was our PWM pins were missing the PWM connector on the Victors. All 5 of the cables that failed were inserted improperly. When we removed them, you could see all 3 pins were very slightly deflected in the same direction, meaning they’d missed their holes. Straighten them out, and re-insert the cable. Use as little force as possible to insert the connector, and if you encounter any kind of resistance, the pins are likely missing the connector and are being bent.

As for the actual IFI-supplied cables failing, we’d yet to have one fail other than from broken pins due to repeatedly mis-inserting them. Carefully re-inserting them always fixed the problem.

Hopefully you are having the same problem we are, and won’t have to burn a hole in your budget replacing PWM cables!


Ok, before we shipped our robot, we noticed that the pwm cables kept falling out of the victors and spikes. Is this happening to others or just us? How should we fix it. I think hot glue. Also was pluging in the pwm cables into the victors more difficult then last year?

Judging from other threads this year, I’d guess that more people had trouble getting theirs seated properly in the first place then having them falling out.

We had problems with the PWM cables making decent connections to the RC.

Hot glue? Ugh. I suppose that’d work, but only as a last resort. Just use a tiny bit (just enough to be able to slice with an exacto knife in the event of a problem).

Plugging the cables in was MUCH harder this year … because IFI shipped em with those little plastic tabs where the cable plugs in. Its a simple fix with a small knife, but cutting into those little $120 blocks of plastic scares the crud out of me.

This years speed controllers and relays gave us alot of headahces too. Alot of the connections were ‘iffy’ at best. Sometimes bending the pins and reinserting the PWM cable into the relay/SC helped, but it never felt like the correct solution. Hopefully IFI knows of these problems and is working on correcting them because the plastic housings are simply not as good as they have been in the past. An ‘iffy’ connection is not okay in my book. I put my trust in IFI to resolve the problem, because they have done such a great job in the past. I never imagined a simple thing would give us so many problems.

We also found the connections on this year’s Victors to be marginal at best. We file down one corner of the cable connector to get it to fit, but I don’t trust it. We’re grabbing last year’s off the old bot and will swap them out at competition, as we are allowed to use ANY 884 model.


our team was thinking of making our own PWM cables next year.

If you want a good result, make sure you use a high-quality crimper designed for the task. I made a couple of PWM cables with pliers instead of crimpers, and I took a very long time verifying the crimp, so they’re okay – but I wouldn’t want to make a habit of it.

I rarely have any problems with PWM cables aside from them falling out.

My team’s worst problem last year is when a PWM cable fell out of an upside-down Victor during a round, causing the robot to only turn one direction and creating a hard struggle to plug it in afterwards.

This year, if one of them falls out (it’s a Y-cable), it could ruin our gearbox, which would basically prevent us froom competing. I think that we should hot-glue them in.

My biggest problem with cables this year is the camera cable.

I already shipped the camera, so I will have to fix it at the competition, but the Camera cables are the worst. They keep getting bent because they have to wrap around to the front of the camera, and the TTL Serial cable is bad because a little bit of plastic on the tiny circuit board got chipped off, and causes it to fall off a lot.

Part of this problem was because some people on our team decided to mount the electronics upside-down on my test bot!

The reason this is so bad is that it causes the code to freeze when the camera stops responding, giving a red flashing “Program State” (Code Violation) error on the RC, stalling the program for the rest of the match. The remote reset button might work, but definately only after Autonomous mode.

If there is any cable I’ll be hot-gluing in, it’s the TTL and the camera power!
There’s still always a switch on the camera itself.

This behavior can be changed. Remove the FREEZE_ON_ERROR definition and recompile the code.

We had so much trouble with the PWM cables plugging into the Victors that we now have a team member who is the designated Cable Guy. He plays the piano and has long, thing fingers. First time every time. We’ll be glad to rent him out for tournaments for a modest donation to our '06 campaign fund… :rolleyes:

We’ve had a lot of trouble this past year with bad NEW cables; I’d even say we’ve had more bad NEW cables than bad old cables from last year. They’re currently tied together in a white box somwhere in some sort of PWM cable quarantine… Some of them just would not work out of the bag.

We have had a lot of problems with these connections. So far I have had to replace 3 pwm cables and 1 speed controller. The alignment of the connector is very very difficult, if not impossible. Be careful if you do decide to help the situation by cutting or filing the corners (provide relief) as the plastic may fall into the connector hole. We found some clips that slide in over the connector once they are seated and under the speed controller body - problem is that we have the speed controllers velcro’d down so they won’t move around.
Still looking for a better way than hot glue to keep those little buggers from coming out as easily.

Replying to my own post. How lame is that…?

We had our arm not operate TWICE during the tournament when someone other than our Designated Electronics Guru and Cable Guy tried to plug in a PWM cable. We lost both of these rounds, but found out that we could really play defense. It was kind of fun watching our modest little wooden bot keep a 12-foot topper from scoring a single tetra, even if we still lost the match.

Of course, the real failure was that we did not detect the bad connection before the match. We bad, the 'bot was sent out to the field without a complete systems check first. This will NOT happen again next year. Note to self: if anyone is working on the robot, the electronics Guru will be the only one allowed to touch the hardware.

A team at Portland (I forget the number, but it was Santiam Christian School’s team) said that they put a tiny dot of silicone adhesive on the connector after it is seated. They say the silicone is easy to remove, but grips just enough to prevent accidents.

We have had problems with pwm cables before, especially last year with the current sensor. It was wired to keep the globe the drives our “fingers” from snapping it’s sprockets and the 5/16" fiberglass rod that made up the fingers.
The connection would get noisy and finger movement became very intermittent and unpredictable. The fix for us was a can of ProGold G5 contact treatment. Sprayed on the free ends of cables and then gently run in and out of the sockets or pins a few times. This seemed to cure all of our PWM and current limiter issues. This year we will be treating all pwm cables before driving as a Standard op.
We will be at Buckeye and West Michigan if you need some I will lend you the use of a can. BTW if your on the west side of michigan you can get it at SF electroncs. Not cheap but good stuff.
Tom Cooper

Our pwm cables never failed us. The little burs on the side of the pwm insert on the victors are for keeping the pwm cables inside so it doesn’t move. If you give the cable some wiggle room and keep it out of moving parts, the cable should be fine.

But when pwm cables do come out, its NOT a good thing, because those wires are live and if it touches metal, you’re creating a short that goes right back to the RC, which is terrible. A fried RC is about as bad as it gets electronics-wise.