Cortex Randomly Reboots

My team was working on our autonomous, but the cortex would often restart as if it was switched off and then back on, and start back from the pre auton. It did this at random parts of the program. I use 1 IME. Is this one of those IME issues? Has anyone found a solution to this problem? I don’t recall having this issue with the driver control, which doesnt use the IME.

I’m not saying the issue isn’t with your code but experience tells me to check the battery connection when that happens.

The battery seems to stay connected to the cortex. I guess it could be disconnecting for a fraction of a second. The backup battery should fix this right?

Most probably it is a loose connection with the batteries. Did you try using a battery extender to the CORTEX, as well as connecting the CORTEX to a 9V backup?

We have had our bot do the same during auton, we fixed it by plugging in our 9V like @CATaclysm Delta_II said.

Are you using the white 2.0 VEXnet keys while having the joystick connected to a computer with the programming cable? We always have an issue where if the debugger window on the computer is left open, VEXnet connection drops soon. Switching to the old black 1.0 keys solved it, and downloading the code with them is much faster as well, but if you don’t have any old keys try closing the debugger window as soon as you’ve downloaded and clicked start.

I use the debugger window a lot and haven’t ever had the robot disconnect… The only problems I have seen is if you don’t let the debugger catch up, it will have typos but I haven’t extensively tested this…

I’ll plug in the 9v backup and see what happens.

We plugged in the backup. But the problem persists. My team thinks there might be some wires shorting, particularly the I2C wire. Could this be the problem? We use backlighting on our LCD, and when I tap some of the wires the backlighting flickers on and off. Any thoughts?

Id just switch to quads or Pots instead of IMEs to be safe. If the problem persists put them back on

That sounds like you might have loose or shorted wires somewhere. I would recommend a thorough inspection of the wiring, questioning any damage to the insulation, loose connector pins, etc.

I’ve never seen such things cause the Cortex to reboot, though; to address that issue, it is worth trying unplugging the IME altogether as @bossgivol said and stress-testing.

You might be interested in this blog post I just wrote today: Why I’ll Never Use IMEs Again. The things you are describing could surely be happening because you have an IME attached to your robot (whether your code is using it or not).

This season, our cortex would periodically “freeze” – just stuck with the motors on in the last instruction, and no more instructions being processed (happened in auton & in driver control). The only remedy was powering on/off. I mention this because you bring up the 9V battery. When we were at States last month, our cortex froze, of all places, on the LCD screen where we choose the auton program (luckily on the practice field, not in a match). NOTHING would get it to un-freeze, including changing the batteries. Until we realized that we had the 9V plugged in, which was keeping the cortex “alive” (and stuck) even through the battery change. Once we unplugged the 9V, it could reboot. After that, we unplugged the 9V every time we changed batteries between matches, just to be sure it was truly powering down.

I hope the post above proves useful. And from your original question, my response would be, Yeah, I’d guess it’s “one of those IME issues.” But since “those IME issues” are completely random and impossible to reproduce, it’s always hard to prove in a court of law…

Leslie Peters, Coach
Team 1666, Renegade Robotics

Check the battery wire connection and check to see if the wire is shorted or isn’t all the way into the cortex, this happens all the time and it is a result of a battery sometimes being RIPPED out of the cortex so be more careful

We just had out states last Saturday, and had flurry of problems starting the morning of the tournament. We were experiencing the cortex randomly rebooting while we where recording autonomous periods, and then again in matches.

We had 2 battery extension cables running our battery to the front of our robot (to provide weight at front to keep from tipping), might this have been the problem? I didn’t think that the vex battery wires would come undone, and we had a charged 9v plugged in (we even tried changing it, we thought it could be a problem).


West - might I inquire if your robot had any integrated motor encoders (IMEs) on it? If the answer is yes, please scroll up, and read the blog post I’ve linked in my comment above about IMEs. It’s basically a reference manual on how IMEs actually work (in robot-savvy-layman’s terms, as opposed to I-build-computer-chips-for-a-living terms), and the litany of random things that go wrong on a regular basis.

If you could post a reply about whether you’re using IMEs or not, I would appreciate it for my own edification. Thanks!

Leslie, Team 1666 coach

Like, is the disconnecting and reconnecting slow or fast? If it is fast, make sure that there are no metal near the VEX key on the cortex. If it’s slow, then most probably I suggest looking at the connections between your CORTEX and your battery.