Potential new field control fault? VEXU simultaneous controller reboot at Kalahari Classic

Yesterday, in the much anticipated Final of the VEXU division at the Kalahari Classic between FOAB (red) and WPI (blue), there were a series of what appears to be field faults in Finals matches 2 and 3.

In Finals Match 2, at about 0:16 remaining, both of the Blue alliance’s (WPI) controllers shut off simultaneously, which is visibly confirmed on the recording:

Ultimately, Blue lost that match.

In Finals Match 3, at about 0:40 remaining, again both of the Blue alliance’s controllers shut off simultaneously, which is again visibly confirmed on the recording:

Ultimately, Blue lost this match as well, and the entire tournament.

The purpose of this post is not to challenge the rulings of the referees or even to say that WPI would have won their matches had these faults not occurred. Instead, my goal is to compile the available information on this topic and to bring it to the attention of VEX employees such as @jpearman and @levipope so that it can be investigated and the root cause can be determined and fixed.

With that in mind, here are a few bullet points of the facts about this situation and how it is different from disconnects or other field faults we have seen in previous years:

  • The new, V5 brain-based field control was in use which uses the smart ports on the controller, not the old field control which uses the larger RJ45 port on the controller
  • The controllers actually turned off, and did not merely disconnect, as shown by the screens turning off in the videos
  • WPI has stated they were running firmware 1.1.2
  • WPI has published their code, which is available here: GitHub - wpivex/SU2022Pros
    • Personal note: I’ve gone through this code and don’t see anything abnormal that could cause this, still it’s good to have others look.

Hopefully, VEX can determine the cause of this, whether it be the new field control or not, and put in place measures to prevent this from happening again, as the results are quite severe.


Did you happen to look at or keep either the field control brain or team brain logs ?
or TM logs ?


According to what the refs said, “the field control system logs don’t say that it’s a field disconnect and instead it was a robot internal disconnect. We can try to also check our brain logs and see what they say.


Obviously all I have to go on is video replay so any theories I may have are complete speculation.

It unusual for a controller to power off (or reset, I cannot tell from the video if the student had to power on the controller again). We see controllers lose radio connection, and sometimes lockup needing manual reset, but generally not power down unless the V5 brain has also been powered down.

statistically, it’s a small chance that a bug in field control would shutdown (how I don’t know) two controllers on the same alliance, at the same time, in two consecutive matches.

What I do notice is that at the point where the controllers turn off a robot has hit the field perimeter causing significant movement.

This is the first frame of controller having a blank screen. a red robot (mostly) just moved the field perimeter.

and the other match

so it would be worth inspecting the cables from the FC to the controllers, perhaps they are damaged, or perhaps pinched in between the field perimeter in some way.


It seems like it’s known that throughout the day there have been numerous issues with the wires on the field control system and having to replace them multiple times, so this could have very well been it.

That being said, if this is the issue then in hindsight it seems like an issue waiting to happen when the wires are put in a position where they’re vulnerable to damage from robots hitting the field walls, which is entirely inevitable.

I wasn’t there, I have no knowledge of anything else that might have been going on, how long the cables were, who made them or how the cables were dressed.

again, just speculation on my part based on watching the video.

We ran 30 fields in the divisions at worlds, 3 in the dome and 16 skills fields. To my knowledge there were no similar issues (a few other issues, but no controllers turning off) and no cables having to be replaced (perhaps one or two damaged connectors, I don’t remember).


These two images show the state of the field immediately after the round of 16 match between BCUZ and EZPZ. If this is how much a metal perimeter can move during a match. I’m very curious as to how much the portable field perimeters (which are known for having a semi-flimsy feel to them) can, especially seeing as they will be used at the World Championships.

That’s a separate issue. Doesn’t look like they were attached to whatever is being used to raise the field.


Yes, as a matter of fact two matches (20 and 17) had to be replayed because robots were able to move immediately after the match was over.

In Q 17, BCUZ’s 15” was able to move immediately after the match was over, and this affected the number of tiles is covered. Seeing as this match was decided by 1 point, it was immediately replayed. The issue was found to be an unplugged wire in the field control system that allowed the robot to move after the match. During the replay that immediately followed, this issue did not happen.

The same issue happened in Q 42, where UWAT’s robot was able to move towards a roller and score it from red to blue.

While for Q 20, MSU experienced a field disconnect issue. In fact, their robots were having trouble connecting to the field control system so it wasn’t a surprise that this happened during the match. During the replay there were no connection issues from them, however no disconnect issues happened.

You are mixing up separate issues.
radio disconnects, smart cable being removed from the controller etc. all should have been logged in the FC andTM logs (and visible to TM operator).

What Levi and I have never seen before is an apparent power loss of two controllers simultaneously (or close to that, hard to see on the playback). A cable disconnect should not be able to cause that, some other type of damage to the cable, perhaps, we will do some investigation next week.


Speaking of radio disconnects, what exactly does “Radio Disconnect” mean on the V5 smart controller? Is that 100% on the team or is that a field issue - or could it mean either?

Technically, the field has no radio running the fields. What the Field Control does is control the state of Pause, Autonomous, Driver mode signaling. With VEXnet Field Control it was signal sent through one of the leads to the Joystick controller (V5 or Cortex in the day). V5 Field Control App does a lot more communication between the field controller and robot’s V5 Brain, which allows logging of events, such as the Robot’s brain signaling a disconnect. The Robot’s V5 Brain will use having something plugged into the RJ45 plug on the controller as a signal to the brain to switch from pit radio frequencies to competition frequencies (to reduce interference from other robots). V5 Field Controller will signal to switch to competition frequencies once you plug the V5 Smart Cable on the driver station to your V5 Joystick Controller immediately or when the field status switches from “Standby” to “Ready”. This latter behavior is setup on the fields V5 Brain settings for the event.

So in this environment, the Radio disconnect logged is likely due to an event on your robot - it can be a loose V5 smart cable, it could be because your radio is buried deep inside a mishmash of metal, or a momentary glitch when your robot take a hard hit on the field (like crashing in the perimeter or other robots).

Do bring these event logs to the attention of the Event operations team - they might not have a strong answer right away, but certainly can help diagnose possible causes and later allow them to look at event logs later…

Be thankful that the VEXnet communication protocol has been much improved since early days when you had to ask pretty much everyone to turn off their phones, even in the audience, and you still had that one person who had to have their MiFi hotspot device running :frowning:

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Thanks Pascal. That is the common sense answer, but I’ve got to believe there is more to it than that. For example, can a faulty cable running to the controller cause a “radio disconnect”? Can they be caused by too many robots on the competition channels?

So too many robots on same channel is a concern that they contend with at Worlds and had skills fields that had a high concentration of fields run bluetooth communication. By design the competition fields run on different channels reserved only for robots running on active fields. @jpearman has posted how this all works on the forum. I am sure he can chime in to correct my misconceptions.

We’re not really sure. There is no generally understood mechanism by which the field control, old or now, would be able to spontaneously cause a disconnect during a match.

However, throughout my 9 years in this competition I have seen too many simultaneous alliance disconnects or even whole field simultaneous disconnects to believe that there is no way for the field to cause one.

You can check out this thread for a great explanation of the older field control hardware by @jpearman himself, as well as a discussion about potential field faults in the 2017-2018 season:

As a ref my rule of thumb is that if no other teams were simultaneously affected, then it was probably an isolated incident to that robot from bad radio mounting, damaged wires, or plain bad luck. Am I 100% sure that the field wasn’t involved? No, but since I have no way to actually verify either way, I have to choose the most likely outcome. If multiple teams on the same field were affected simultaneously and it arguably changed the outcome of the match however, then that’s worth looking into a replay for.


I’m pretty sure. The most likely causes of radio disconnect are either poor radio placement, damaged hardware or some environmental condition (don’t run microwave ovens at events).


Dude, you are killing me! our volunteers depend on the non-stop appetizers we serve them fresh from our 1950s Radar Range!

(sorry - humor-ish)


My favorite Aunt had this and it was amazing, popcorn in moments, bagel bites, hot chocolate chip cookies, etc. So are you saying that when she pressed start and the lights dimmed and Uncle Chazz grabbed his chest, it was all related?



A Raytheon Radarange microwave oven aboard NS Savannah, installed circa 1961.

The galley has an early generation of microwave oven so the ship’s cooks could “nuke” food long before that shortcut became commonplace in American homes. 2


ok, let’s make that the last microwave post and get this topic back on subject.