Cortexes with lung cancer

@jpearman
In the past, our cortexes have inexplicably started smoking during use or testing. Our usual procedure is to label the cortex “BAD!” or “FIRE!” in red sharpie, and leave it alone for the rest of eternity, but it happened again to a new (~4 month old) cortex this morning. I was across the room at the time, but @jwwood13 might be able to tell you what he was doing to our poor cortex. Cortexes are rather expensive, so I figured I’d ask to see exactly what went wrong, and how we can avoid it in the future.

I took the casing off, and took some pictures (with my crappy phone camera, sorry). Whatever happened, it was hot enough to scorch and warp the plastic casing. The burn is the white thing, near “U15”. Can you help me at all?

Thanks in advance.
cortex1.jpg
cortex3.jpg
cortex2.jpg

Yea, perhaps some light next time.
So I see in picture 3 U15 looks toasted, that’s part of the H-Bridge for motor port 10. So you probably shorted the port 10 two wire output somehow, frayed wires on the motor etc.

cortex port 10 killer.

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Ok, thanks!

So is the rest of the cortex safe to use (assuming nothing else is broken)? What happens if we tried to use port 10 again? Is there any way to (legally) fix frayed motor wires?

Depending on how damaged the actual PCB is, it may be possible to have someone rework (ie. replace the bad components) for you. VEX service may be able to do this, but will probably charge you. I have put students here in LA in contact with one of my former rework houses and they performed the work reasonably inexpensively. The parts are cheap. So if you can find someone local in Arizona you may be able to get them repaired.

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It’s a grey area, i’m not going to offer any advise here. Perhaps use a motor that does not work for parts. Best thing is to be gentle on the motors so damage does not occur in the first place.

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Alright, thank you!

I don’t know why you blame me. I was just using the debugger to test all the motors before we started testing the robot to make sure they all worked. At the time of the incident, the motor I was testing was in port 4 (5?), and everything was functional. Mostly, anyway. I can probably send detailed pictures of the motor and the cortex on Tuesday. Also, @puzzler7 Why, are you taking photography, if not to be able to take high quality pictures of the robot with a good camera?

@jpearman I got so caught up in the helpfulness, I just realized you didn’t actually answer my question.

@jwwood13 I’m taking photography so I can tell my teacher I’m taking pictures of my robot and then I have an extra hour each day to work on the bot.

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What we do with frayed motor wires is as follows. We have yet to be told it is illegal.

  1. Remove the green cover or IME from the motor.
  2. Separate (pull apart from each other) the red and black wires within 2-3 inches of the fraying.
  3. Tightly wrap a small piece of electrical tape around the frayed region of each wire.
  4. Re-attach the cover or IME such that the groove for the wires tightly clamps down on the electrical tape to help hold it in place.

Probably, just keep an eye on it.

Thank you!

That’s what we’ve always done… if it is illigal then we’ve never been caught… he he he ;}

If it comes to it, it should be legal to solder on new wires from another motor (or sensor).

Don’t think so.

See the official Q&A ruling:
https://vexforum.com/t/answered-clarification-of-r15-a-ii/35371/1

wow, that’s ridiculous, but karthik has spoken…

he didn’t even answer the 2nd part of the question, which seems to me an encouragement for low budget teams to repair wires in a way that isn’t legal (though I’m not saying it’s the right thing to do).

U13 and U15 control motor ports 1 and 10 In most cases a visual inspection will reveal a small white area on the chip or if the short was bad an obvious distortion. These FET chips are SMD and very difficult to replace, but it will fix the issue 9 times out of 10. Digikey did have the OEM part number and you can still look it up for alternatives.

OEM F05 FDS 4935BZ

NOTE: This is a mini soldering repair and unless you have very good soldering equipment and a way to magnify while working, not recommended for most.

Also: I have no idea if this would DQ the bot from competition as it is a user modification.
Contact me if you have requests or issues.