393 motor design flaw

the other day we turned the robot, then tried using the lift. It didn’t work. We see smoke emitting from the robot and find that i’s from a MC29. We examine the motor, it shorted out. We find that it is in part us not treating the motor as well as we should but also becuase where the wires enter the motor they are not insulated! Why are the wires not insulated here? I can’t think of any reason, can anyone else?

In a 393 motor, there is insulation covering the main wires. There is also a small rubber piece on the back that helps protect the wires as they enter the motor to prevent what happened in your case. After wear, the rubber thing will break which can increase wear on the wires insulation possibly causing a short.
One way to solve this problem is if you notice copper on one wire, take the top off, and tape over that area on each of the wires. This will allow them to not short out.

thanks for the suggestion but there was no insulation at all under the rubber.

maybe it cracked and slid down the wire

Can you post a picture?

I’ll do that later today when I go to program.

This seems to be a terrible design flaw with the VEX motors. That #&^% rubber piece breaks if you even look at it wrong.

I know and out team can’t find replacement parts so if anyone has a link please post it because we have like 100 motors with that missing and other than that they are perfect.

Even if you found the replacement part, I do not think you could install it because it would not fit over the pins of the motor. (even if you removed the keyed connector to install)

Tape in my opinion is the best, fastest, and cheapest solution.

another option for repair is sugru or instamorph. Instamorph is cheaper but less flexible than sugru but you can make your own sugru cheaper than instamorph.

If fixed with these methods would those motors be VEX competition legal?

here it is, a little blurry becuase we forgot to bring a good camera and had to use a phone.

<R7> I states:

So yes, you can also apply it to strengthen the wire to prevent a short from happening. I plan on buying some instamorph for this purpose, and I want it for a non-vex related project.