VEX Wireless Channels - Large Competition Tip

Just wanted to share this quick tip I heard from a VEX veteran with all of the teams around the world entering really large events. So the VEX Net keys have 250 different wireless channels. Of those, 150 channels are reserved for field control systems like the control switch. This means that only 100 channels are open to wireless. So… if you plug in your controller before turning it on, you will have access to those reserved channels. However, if you turn the controller on before plugging it in, you will be on the same channels as everybody else, not playing in your match. This means you if you lose connection, you may not be able to regain it as someone may have taken the channel you were using.

Every year this problem comes up at my state tournament and the more people that know how to fix it the better. Let me know if my understanding is wrong in any way.

Thanks for the heads-up?

Sorry, I’m a little confused on ‘plugging in the controller’ - do you mean the vexNet key before turning on remote vs after or??

Plug your controller into the driver interface at the field before turning it on.

AH!!! NICE - I get ti now! This being said we often have issues with the robot/controller pairing at competition - could it be that VexNet is trying to find an open channel then?

This is slightly misleading. I’m not sure what the specifics are on the numbers of reserved channels vs non-reserved, but the field control systems are physically connected with the tournament manager hardware and the controllers; they don’t use wireless (VEXNET) or the channels.

As I understand it, when a VEXNET transmitter is plugged into a competition switch or field control tower, it will opt to select from the larger pool of “reserved” channels that are specifically for competition use (which is important for large events where there can be potential interference from so many teams running their robots). All VEXNET 2.0 channels (I thinK?) are also separate from standard WiFi devices and shouldn’t receive interference from them.

if we plug into the towers before we connect to vexnet it disables our controller and robot so we can’t select autonomous on the LCD screen. How would we be able to work around this?

Just let the robot connect, select your autonomous, and then plug into the field :slight_smile:

Thats what we usually do but the op is talking about how plugging in before you turn on gives you a more solid connection.

Oh sorry I didn’t read the rest of the thread closely enough. My bad. For the work around then I’m not entirely sure. I guess you could modify the competition template but that’s generally ill-advised. Other than that I’m not sure. I’m not the greatest expert on how the vexnet system works lol

It’s not a huge deal, but when you do the math and look at larger competitions, it becomes a factor. Let’s say you have 100 teams at an event. If they all connect and then plug in, only a fraction of the channels are used and if you lose connection, you may lose your channel. If you plug in then turn on, you won’t lose your channel as only 4 of the reserved channels are in use at a time. It’s a small thing but it’s these things that will decide if you win or lose some matches.

Like I said earlier how would I be able to use this if I need to connect before I plug in to select auton on lcd screen

Put your corresponding code in the initialization function.

Have a read of this thread.

That references this post.

If you plug into the field control system before turning on your controller you will connect to a competition channel. If you do it the other way around (ie. turn on the controller first) then you will initially be on a pit channel and as soon as you plug in the RJ45 cable you will be switch to a competition channel. The only adverse effect this has is to cause a cortex reset so any initialization code will run again.

Is that for RobotC only? I don’t seem to have this happen with my PROS code.

I don’t think I’ve ever seen this happen with either RobotC or PROS…

I may be wrong on the cortex reset. You will see VEXnet disconnect as the system changes channels, but perhaps this doesn’t cause the code to start over, now I will have to go back and verify.