V5 Disconnecting and not Reconnecting

So I’ve seen reports of the following exact symptoms before but I’m not sure if a fault was ever found:

  • V5 Radio lights go solid red
  • Controller display goes red
  • Will not reconnect even after a controller reboot until either the program is ended using the button on the V5 or the V5 is rebooted, I’m not sure which (I’ll update the post if I get clarification)

@jpearman I know there have been various posts about theses symptoms going back to at least 2019 but I can’t seem to find anything on the root cause, can you provide any insight? Most importantly for the teams out there experiencing this during matches (which prompted this post), is this a VEXnet and / or VEXos fault or are the teams to blame.

Also, while I’m here I’d like to ask if we could get an easily accessible updated document like the old cortex troubleshooting flowchart specifically related to the status codes the V5 system can produce, (ie. radio lights, controller display colour, etc…) or at the very least a list of radio light codes and information on what causes the controller display to go red. This was always a super useful document for quickly diagnosing issues and it’d be great to have an updated version.

Thank you.


I don’t remember anyone reporting that specific condition.

Radio lights going red, controller display goes red.

This would suggest no controller to brain connection. The only time this will occur and perhaps confuse teams is at the end of a match. Once the field control cable is disconnected at the end of the match, the system disconnects from the competition VEXnet channel, the brain will not reconnect to the controller until it has been power cycled (or field control is plugged back in). But the match is over so the expectation is that robots will be turned off anyway.

is this a VEXnet and / or VEXos fault or are the teams to blame.

I don’t think either, we have no control over the RF environment the robot is run in, it could just be interference from the microwave making popcorn or something like that. We encourage everyone to disable 2.4GHz WiFi and other sources of interference, but I’m sure at many local events that doesn’t happen. Teams can help themselves by locating the radio in a good location on the robot, making sure wiring is good, no broken connectors etc.


It happens to our V5 on a regular basis, I would estimate around once per every three hours of practice or competition time. The robot will not reconnect until the V5 is rebooted.

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Ah, these are the threads I was thinking of but it seems like for most of them rebooting the controller did fix the issue:

As for what teams can do, in the case that promoted this the radio was mounted high up and the event is Ontario Provincials so external networks are kept to a minimum; though I understand that there’s not much you can do with this information.

For worlds this year we will be using a new field control mechanism (and that doesn’t mean TM is changing or anything like that). As part of testing that system I was running several systems back in January for many hours running back to back matches, the only small issue I found when doing this was sending text constantly to the controller could cause it to drop a connection. This would happen on a single system after perhaps 4 hours of running, so after I had run around 100 matches back to back without turning off any of the systems. We have improved that for the vexos 1.1.1 release, the final test I ran back in January was something like 1200 matches back to back without a single VEXnet drop or issue.

Do you send text constantly to the controller from your program ?


No. We don’t display anything on the controller screen.

There have been a lot of vexos, radio and controller updates since 2019.


Yeah, I know I just figured it might be related considering how similar the symptoms were from an outside perspective. Also, I was slightly wrong in my original post, the team didn’t try to reboot their controller so that may or may not have fixed it.

They do display text on the controller and print to the debug console but it’s rate limited such that it has never been an issue.


It happens to us too, but a lot more frequently, some days like every other time we test the code, other days like 1 every couple hours

Do you download wirelessly and then disconnect the USB cable ?

If so, the radio will switch back to a normal radio channel (ie. what we call a pit channel) from the higher speed download channel 10 seconds after the USB is disconnected.


So if I keep the usb cable in it won’t do that?

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