Burnt MC29

At the end of the tourney we hosted a few weeks ago we found a MC29 that doesn’t work. We opened it up and found this

So what could cause this?

My guess would be a dead short. Perhaps the wire was nicked somewhere and touched the metal of your robot.

Otherwise, chalk it up to the fact that electronics will go bad eventually. We have had a few MC29’s go bad, but considering how long we have used them I don’t consider it to be a problem at all. With students handling them, I"m a bit amazed this doesn’t happen more often.

This happens sometimes and it’s usually due to a short between the positive and negative wires of the 2-wire motor cable. This can happen because the cable is damaged, for example after it gets chomped by a gear.

A motor controller 29 contains an H bridge, which is a circuit component like this:

This is what allows the motor to go either direction. The switches are made from transistors. Those transistors can’t take the current load that they get when the circuit is shorted, so they are usually the first part of the circuit to fail. Which is good, because it means that shorting your motor wires together will only destroy your MC29, and not your cortex :rolleyes:. Do NOT short your motor wires in ports 1 and 10.

Another thing: a possible symptom of this problem is a motor that goes in one direction and not in the other direction. If you notice a motor doing this, especially if that motor is in port 1 or 10, STOP WHAT YOU ARE DOING and check for a short before you continue.

See this thread.

It has a good photo of an abused motor, the type of thing that can cause this to happen.

We got one of these to overheat so much it set of the smoke alarms at our schoo.:eek:

ok, good to know. I have another question. Is it possible for a VEXNet connection to be only partially disrupted? I ask this because at a competition we were at on Saturday parts of our robot were not working very in the room that the fields were in but worked fine in the pits. We don’t think it was a PTC in any of the motors because we put freeze spray on our motors before matches and they were not warm after the matches. We also ruled out it being the internal PTC in the cortex because stuff on both power banks were working.
We had heard that a team was live streaming their matches from their GoPro and other teams were having similar issue. Later it seemed to be fine, or at least it stopped working in the pits as well as the gym the matches were held in (we think it’s a bad motor, MC29 or lack of bearing blocks).