all motors twitch/ loose power quickly

Okay so my team is qualified for vex worlds and we have experienced this really strange problem for the last five days:

When you turn on the robot and run it, it runs normal for about 25 seconds then the entire robot starts to slowly loose power until motors either a) continue running b) stop running or c) start to twitch. If you stop controlling the robot and let it sit for about 15 seconds and then drive it runs fast and normal for about 20 seconds and then starts to lose power once again. The robot is significantly loosing power in the lift (4 motor 7:1 speed) so much that it can barely lift or lower — despite the rubber bands that help lift it. * THIS IS ONLY NOTICEABLE WHEN THE ROBOT IS CARRYING GAME ELEMENTS OR HAS BEEN CARRYING A LOAD* In addition, once the lift become wonky the base also starts to have issue and wheels may just stop running, keep running normally or twitch.

Stats about base:
six 3.25 omni direct drive turbo

Thing I have already done to locate/ fix the problem (all futile fyi):
-replace the cortex
-replace the power expander
-unplug each port one at a time from the cortex and test to see if the robot while carrying a load will start experiencing this problem. I found that by unplugging every port the problem continues, therefore I assume its not a motor problem?
-added backup battery
-replaced batteries at least 12 times (due to continuous testing)
-replaced joystick batteries
-unplugged all potentiometers and encoders from cortex
-downloaded old code from 2 weeks ago that was used at state
-replaced all the motor controller on the 4 motor lift
-took off the 4 motors from the lift and checked the sauntering inside and the internal gearing along with the direction they were spinning
-changed motor internal gearing to torque - the problem is still seen in both the base and the lift
-change breaker distribution
-The power expander now has two lift motors plugged in and two base motors plugged in

I am very confused plz help lol

https://docs.google.com/uc?export=download&id=0B8QakrQz3mNkajRYbmZLdTBqVUtmVDBpYjkzXzZtbGdLSWNr
https://docs.google.com/uc?export=download&id=0B8QakrQz3mNkZGRaeG90cWNMdnlibHJJbWpRYnpXSHk0YUxZ

*please note for the base video 4 motors are running normal, 1 is twitching and another has completely stopped rotating

Could you post your code? I’m inclined to think the issue is with code (even though you tried old code that I assume worked fine at the time but also isn’t working now)

Edit: Also make sure your wheels aren’t rubbing against the plastic anywhere. It looks close.

I’m inclined to believe this is burnout, at least it sounds like it. Check for friction?

you may have a short somewhere, check your wires, also, about friction, is there only one side supported in your base, or is there polycarb supporting the other side?

@wesleywong how should someone approach locating an electrical short?

Search for any and all damaged insulation/exposed copper in the wires.

The attached image shows a common location of the problem.
Damaged wire.PNG

Chain the base wheels together so that either they all run together, experiencing the same load, or they all stop, which is unlikely to happen. The lift just sounds like too aggressive of a gear ratio. Try running each motor individually to make sure they all are running, or switch to 1:5 torque.

Yes it does definitely sound like a short. One question: Is it all the motors that stop working and twitch or just a few of them?

The twitching and returning to power after several seconds indicates you are tripping breakers in the cortex and/or power expander. Try rearranging how your motors are wired to spread the load equally across the 3 breakers- one for ports 1-5, another for 6-10, and a final one on the power expander.

If you do this and the problem persists, you may need to find a way to draw less power.

Replace the cortex