Burning Cortex

Hi VEX community,

Today my cortex caught on fire. This really sucked because today is the day before states. Anyway I just wanted to know why my cortex got fried. Our team just got a brand new cortex and I don’t want to fry it like the last one. The motor configuration consists of 4 flywheel motors, 4 drive motors, 2 intake motors, and 2 lift motors. In our double flywheel the left two motors are connected to ports 2 and 9 and the right two are connected to 4 and 7; our intake is connected to port 5 and 8, the lift to 3 and 6, and the four drive motors are y-wired to a power expander in which it goes to port 1 and 10.

This is just a theory but I think that my drive configuration caused the cortex to short. I don’t think that you can actually y-wire into a 2 wire port. I made it so that the 2 wire extension (going into the cortex) went into specific colors of the 3 wire extension (going into the “in” port of the power expander). The drive motors were connected to the same colors as the 2 wire extension. I understand if this is confusing.

I also think that both the PTCs of the cortex probably shorted. Our robot is really, really. REALLY heavy so the drive motors probably need more current to drive the robot. When the drive motors are y-wired the electric current exceeds the 4 amps of the PTC and therefore the cortex catches fire.

These are probably not why my cortex smoked but its a theory, a VEX THEORY. :slight_smile:
Please Help,

So it actually just caught on fire? I don’t think it’s anything you did if it’s that. Could have just been a defective cortex.

How long have you had the one that caught on fire?

Also could you send pictures?

I’m exaggerating. But you could actually see the smoke and smell burning plastic.

Sorry I can’t send you pictures because we already replaced the cortex. But I could send you a picture of the configuration that I used.

Oh and we’ve used the cortex for probably a month.

Do you still have the one that got burned?

As i said before in my opinion i don’t think you die anything majorly wrong

Yes we do. It’s in our robotics room right now, so if you want pictures of it you’ll have to wait until tomorrow. Do you want pictures of the inside?

I would recommend taking a bunch of pictures of the inside and sending them to Vex Support to see if any of their technicians can see what went wrong

Ok. That seems pretty logical. Thanks.

Could it have been exposed to anything other than a nice indoor environment such as wetness/moisture or potentially metal shavings or something if you were cutting metal? This happened to one of our teams a while back when they took their robot through the rain.

Not at all. I wanted to show my teammates the flywheel performance after I changed the PID constants the night before and that was when I started smelling burning plastic.

We had a cortex melt down when connected to a motor that had a short. Check for frayed wires along motor paths. I have heard also that sometimes shorts occur right inside the motor box from having wires pulled on.

I currently have a couple of Cortex that well have to go in for repairs.

Did this ever actually control all 4 drive motors correctly? Regardless, this configuration is almost certainly the problem. Don’t try to Y of off ports 1 and 10. Also don’t try to run ports 1 and 10 into the power expander.

We make it a policy on our teams that ports 1 and 10 are only used for low power, non-stalling, applications, since a $10 controller is much easier to replace than a cortex when it burns out. Also, inspect the wires carefully where they enter the motor because they tend to break at the strain relief and short out. The short at this point is the most common cause of magic smoke in a motor controller.

We had the built-in MC in port 1 burn out on a cortex earlier this year caused by the motors wires wearing thin and shorting out at the point where they enter to case.

Do you know why you can’t Y off to port 1 and 10? I can send you a picture of the configuration of the y-wire soon.

ports 1 and 10 are H-bridge motor drivers that will directly drive a 2-wire motor. The power expander is looking for a digital signal going in, not a variable voltage from a motor drive. Also, not positive since I don’t have the schema, 1 and 10 drive power signals up to the battery level, not the required controlled 5 volt level.

I’d be surprised if you didn’t burn up the power expander too.

BTW, it is against the rules to Y-off of ports 1 and 10

In my clubs experience, cortexes will burn out like that every once in a while. For example, my team was testing 2 motors and the cortex stopped working and we smelled burnt electronics.

Y-cabling off ports 1 and 10 killed your cortex and the power expander. Custom made y-cables are illegal, custom wiring / electronics of any kind are illegal. Sometimes to prevent teams from having an advantage, sometimes to prevent teams from destroying valuable components.

Ok, I’ll make sure that my club doesn’t do that. Thanks.