Motors inexplicably stopping mid match?

At my last VEX competition (Feb 3rd 2018) my team had a major issue, our drive motors would die and refuse to function the rest of the round, but it only occurred in the match arena, (ran perfectly in the practice arena both before and after the match). The motors worked fine for the most part if we didn’t go for 20pt, but if the drive motors passed the 10pt bar then they would entirely stop working while every other motor on the bot worked.

We have considered the problem being a PTC trip but the motors wouldn’t reset until we unplugged the remote from the competition arena, suggesting it to be an issue with the competition software or something more convoluted.

The hosting school had built raised platforms for the competition arenas, but not the practice or skills arenas, these may have interfered though we doubt it.
We use a partner controller, our coach dislikes this and suggests it to be a potential issue, though the drive controls are on the main controller and literally every function but the drive motors work.

What we have tried and effects:
Replacing the motors with brand new ones > No change
Trying other motor controllers > No change
Removing the drive motors from the power expanded and connecting them directly to the cortex > They last slightly longer, but not fixed.
Checking entire code, resetting the cortex, and updating to the latest code > No change
Using different ports on the cortex > No change
Using different VEXnet keys > No change

My theories:
Ambient heat causing motors to trip PTC sooner, higher motors on the bot have more airflow and thus stay barely within the temp, hence why the motors wait until trying to power their way over the 10pt line to die, as there would be less airflow with the reduced speed. (The room was the smallest we have had a competition in and was easily the warmest, likely close to 80 degrees if I was to guess.
Possible issues with the material of the platform may cause increased interference in the corners of the arena where more material is present in the structure. Main reason for this theory is that several other teams were having massively increased VEXnet disconnects mid tournament matches compared to the amount they would normally expect.

The last tournament for us is in about two weeks so any support would be appreciated.

We participated in a match last saturday and we disconnected 3 out of the 8 matches we played for a few seconds then we would reconnect, it’s very strange, and my partner would disconnect the same time we would, idk if it has to do with batteries, competition switches, or wiring.

How many motors did you use on your wheels? Did you gear/use chain on them for more speed? What was the internal gearing of the motors on the wheels and how much does your robot weigh? Is it heavy?

We run on two rear drive motors, they are using muti-directional wheels directly (no gears or chains) and we use factory internal gearing, no turbos. The bot is probably close to about 2-8 pounds.

There’s your issue. You need more than 2 motors to run on field. There’s too much friction in drive trains and wheels and contact with game pieces and other bots.

This sounds EXACTLY like what happened to us at our states (and I’ve been seeing many complaints about it). We were running 6 high speed gear motors and just like you stated, it works fine before and after the matches (we tested it again at home and it works). We know the competition switch is only supposed to act as a kill switch, but maybe there is an issue with software? We tried everything you stated and even borrowed a Cortex from another team but the issue still remained. It’s really puzzling us and it sucked because our robot was able to score a lot in practice.

I would agree with you, but it works literally perfectly in the practice field using exactly the same everything.

2 motors torque can only efficiently move 14.76 pounds, and i guarantee your robot is more than 8 pounds with two batteries and a mobile goal. Try adding two more motors.

I won’t comment directly on any particular robot, but I would like to note that I see a lot more wildly-over-geared robots the past couple of years than I ever did in the past. It’s not VEXnet, it’s your robot – most of the time.

Two motor drive doesn’t work. Ever.

We are now trying to using a gearing to fix the issue, and I don’t think it is a VEXnet issue as everything else still works fine on the bot when the issue occurs.

It worked in three separate fields at a higher intensity each time and at the prior competitions before this one, AKA, It literally works in practice, but refuses to work as soon as we are plugged in for this competition.

Did you check if the competition port is broken on your controller? Simply plug a network cable in and if you can pull it out w/out depressing the tang this is your problem.

This happens a LOT!

A quick fix is to put an elastic around the controller and thread the competition cable under it during the match. For $50 VEX can repair it.

If you motors are overheating & there’s nothing wrong w/mechanism you may want to look into limiting your motor speeds to ~100 or look into JPearman’s smartMotor Library

I would recommend trying 4 motor drive. The extra motors should ensure it doesn’t stall

literally us this last comp. We could’ve easily been top 10 after quals but ended up bottom 10.

We have tried to fit 2 more motors in, but they dont fit in due to the width of our mobile goal lift.

In and of itself, this cannot be the cause of the problem, as no electrical change occurs as a result of the latch breaking.

No, but w/o the latch, the cable is often improperly seated. Check the shape of the pins in the connector, they pretty much push against the plug insertion. The cable (or rather some pins thereof) then intermittently lose connection…

Should that really matter? When unplugged from a competition the controller functions the same, it doesn’t reset the connection or force the controller to pause right? Would the cord coming out just mean they cannot stop you from driving?

me in finals match #1 last comp as team captain

I believe it is crucial

From what I gather the competition plug pulls some pins low and the competition library looks for this - my guess is to prevent tampering/cheating.

Should the loop open mid-match the robot would stop.

Here’s the schematic -