JPearman's explanation of field control

There have been a number of questions lately on the Forum concerning losing connection during a tournament match, and various people figuring that the system itself must have something to do with what’s going wrong.

I’d like to repost this in-depth description from @jpearman from a few years ago. Please read if you have ever had connection issues. This post goes from soup to nuts, about how the joystick, vexnet, and tournament hardware and software systems work together.

And be prepared for the realization that many if not most of the problems are probably from your controller, robot, or custom code rather than the field control.

Yep. Once you understand how it works, you have to come to the conclusion that the problem is very very likely on your end, not the system’s.

We have had a couple of legitimately dodgy field controllers passed around in the UK. We do of course blame the feild controller first but often it is stuff like not plugging in power expanders or code which makes the robot not work.

@world here we come

Are they really dodgy though?
The amount of teams that blame field control and still blame it even when:

  • You show them that their joystick is not plugged in because they broke the clip and the cable just falls out
  • Their joystick batteries are dead
  • Their robot battery is dead
  • Their battery backup is dead
  • They spent the last 2 matches dragging their poorly secured robot battery around the field and now the connector on their Cortex is broken so every time you tap it, the power cuts out
  • The USB socket for the VEXnet key is damaged so any vibration or a slight tap causes VEXnet to disconnect
  • Their thermal cutouts in their motors have tripped (but it works when it is not in the field officer, on the nice shiny hall floor where there is no friction)
  • etc.

There is one issue which I have never been able to resolve where some laptops just hate the match controller no matter what power saving settings you use, and occasionally will just disconnect from it. This does of course cause the driver interface to do some funny things. Normally, this means disabling one alliance and locking the other in driver control…

Legitimately dodgy. Would randomly and repeatedly disable one alliance mid match. It happened at a few competitions and in many matches. It would show the disable light on on the feild controller.

I didn’t run the events where the issues happened but they were recognised and the match’s were replayed if necessary. It could be an issue with their hardware but it’s been a repeated issue.

Looking at the condition of a number of remotes during competition, certainly it is a team issue in most cases. However, I would imagine it is the controller from time to time, like during the World HS round robin finals matches last year. Hoping when V5 is full implemented the issue goes away, but that is a few years down the road.

That sounds exactly like what I described in my post.