Motor Controller 29 On Fire

During the meeting today, my team was wiring the robot and one of the motor controller 29s quickly overheated, started smoking, then eventually caught on fire, melted the plastic case (I thought the fire was going to stop eventually but our coach thought differently and told me to unplug the wire, and as far as right now, he seems to be correct since the fire only grew bigger before I unplugged the wire).

Did this ever occurred to any other team? Or is this an isolated case?

The motor controller 29 is connected to a power expander, along with 3 other motor controller 29s that’s connected to other motors. There shouldn’t be any issue with the motors / power expander ports since they had been used in competition without failure previously.

After putting a new motor controller 29 on there, everything work fine. There was no overheating, smoke, or fire.

What might cause this incident?

Also, this brings up another question, what action should be taken if a robot started on fire in the duration of a match?

I’ll attach the pictures tomorrow.

If something like this happened during a match at a tournament that I was running, the match would be stopped and the issue would be dealt with. Safety is far more important than any other consideration.

Did you ever have to do any wiring repairs on it? That’s all that I could think may have happened.

Can’t say I’ve heard of it in Vex competitions, but I saw several failed motor controller 29s in the BEST competition. - No fires thankfully but the controller seemed to overheat and fail.

Cheers Kb

Yes, last year this happened to our team. Not quite certain about the exact cause, but we were pushing our 393s pretty hard when one of the motor controller 29s started smoking. After we replaced it, though, all was well… gave us quite a scare though.

And just some additional information, it was attached to the power expander and we had filled up all the motor ports on the Cortex while using the maximum legal amount of power (6 269s, 4 393s).

Hope this helps.

I was still in the testing stage of determining where the motors are running the correct direction when the incident happened. So there shouldn’t be any power problems.

Also, I noticed the motor with the motor controller 29 that caught on fire “locked Up” when the controller was overheating itself.

this happened to one of our motor controllers as well
the motor wasnt working properly and when we touched the motor controller, it was very hot!
luckily it didnt melt, smoke, or catch on fire
when we replaced the motor controller, the motor worked and everything was fine.

at that time, we had a single battery, old pic, crystal/radio,and only 4 motors hooked up

We had this happen a few months ago with the Cortex H-Bridge instead of the motor controller. A similar situation occurred in which a smaller fire started, however this was stopped before it got out of hand (and the cortex still works fine now except for the 2 wire ports)

We believed it was caused by a large draw of current on the H bridges (which are also present on the motor controllers) as is what seemed to start the fire with the large draw of current from 2 heavy duty motors

I’ve seen a number of Cortex H bridge burnt out, particularly by rapid forward/backward changes with BEST Large motor loads.
Sometimes a puff of smoke, but no fires.
Two years ago, there was (reportedly) a firmware problem that allowed “shoot-through” current on the H-bridge in the Cortex.

US consumer electrical plastic compounds are generally required to be “self-extinguishing”, so removing the heat source by unplugging the battery, pulling the wires, etc, should put out the fire.

My understanding is that there are thermal breakers in the motors to keep them from over heating, and PTC current limiters supplying a branch of 4-5 H-bridges.
Worst case condition would seem to be two heavily loaded motors on a Y cable to the one H-bridge, with no other motors in use.

I don’t understand the description “Lock Up”, please use other words, eg:
“motor stops, doesn’t respond to commands to move,”
vs “motor keeps spinning, doesn’t respond to commands to stop”.

Other good reporting practices:

  • What is motor application? lifting an arm or mech? drive train?
  • What is motor hook up? Y cables? motor port? expander port? battery type?
  • What serial number, revisions, other markings (if still readable) on mc#29, motors, power expanders, Cortex/Pic?
  • What type of code is driving motors? EasyCv4 Tank4, Custom PID RobotC arm potentiometer feedback?
  • What exact (not just “latest”) version of EasyC or RobotC is in use?

I’m surprised to hear that. Aside from the firmware problem that you mentioned, I’ve seen very few controllers in the cortex burn out.


Personally I have only seen a few motor controllers with damaged H-Bridges, when they overheat they simply smoke a little and sometimes the plastic melts around the H-Bridge… but no fires.
Also as a general rule of thumb, is recommended to shut off the power supply on any electronic device if it starts smoking or smells like smoke.

If the Motor Controller 29 is still under the 90-Day Warranty, you should be able to get a replacement by sending an email here:

Sorry about the inconvenience.


i had this experience last year. we plugged the controller into our robot directly from the package (as our previous one had broken) and then we saw black smoke come out of it. we unplugged it immediately and the problem appeared to stop.

Its easy to burn out H-bridges if you let the motor leads short together.
So “Don’t do that.”

We changed the rules for BEST for 2011 season to

  1. require face-mounted motors. Clamp mounts can fail and let the motors spin which twists the wires, increasing likelyhood of shorts.
  2. require avoid Cortex ports 1,10.
    Now failures will be in #29 motor controler, which is a $10 part, no $150.
    Plus we can keep using Cortex with burnted out ports 1,10…

Count us in to the fun too. Our motor controller lit on fire at a recent local tournament :slight_smile:
It was plugged in to a 269 motor powering half of a 3:1 geared down lift on one end and plugged into the power expander on the other end. We were nudging the lift up and down with the joystick, and I saw smoke coming from where the motor controller was bundled with some other wires underneath some anti-slip mat, and I turned off the robot and unplugged stuff as quick as I could. Sure enough, there was a big hole melted through the side of the motor controller, and it was right over a black chip about 1/16" square or so.
We had 10 motors plugged in (4 393’s and 6 269’s , but two of the 269’s weren’t being told to move by the software). The Power Expander had four motors on it including the burnt out controller and one non-active 269.

This happened to me as well. I turned on the robot, and began to drive it, and I noticed one side of the drive was working intermittently. I then noticed smoke coming from the robot, and immediately yanked the battery out. Turns out the motor controller for one of our high strength motors on our chained drive had burned out. It melted two holes in the plastic.

We have had 2 in our club catch on fire and a 3rd almost went up until we unplugged it.

I really don’t know what it is you guys do to your motors for this occur. This has never happened to me.

The second one we believe it may have been caused by a pinched wire on the teams lift. We are still unsure of what caused the 1st fire.

i was at Nationals okay NATIONALS!! and my cortex caught on fire not once… not twice… but three times and my teammate controller caught on fire too

Your cortex did? As in the “brain”? or a motor controller?