VEXnet issues

We’re still pretty much a novice team, as this is the beginning of our third season and instead of susing a solution, we have often just replaced the suspect part with a new one. Over the last 23 months we have purchased (as of 2 days ago) 10 VEXnet keys.

I recently posted a message on the “Ask the Staff” forum and Eli has been great in directing us towards a VEXnet probable issue (whether it is interference or faulty keys). As well Karthik as been helpful in getting us off the back-order queue with two new keys, so thank you…

But other than our first three keys (that we brutally abused) we have been especially careful with the rest. Yet, we have outlived five other keys and are now beginning our adventure with the next two. As I have explained in my previous thread, the team does use the keys without rest during long autonomous programming tests, drawn-out driving bouts or other such seemingly endless repetitive tasks only pausing to swap out batteries.

Is this a form of VEXnet key abuse? Should we only be using them in short spurts with long rests in-between? Is ten keys in that time frame, excessive?

What’s been your experience? How do you use (or abuse) your keys?



I was watching the other thread and think Eli gave good advice. I do think that the suggestion of WiFi interference is most valid. I wouldn’t write off the keys until you can verify them in another environment.

Normally the WiFi channel selected will either be channel 6 or 11, when the field control system is connected it changes to channel 1, this stops teams that are practicing at events from interfering with matches.

At the school where out team meets, we have good days and bad. Sometimes there are many disconnects, sometimes none at all. As well as other WiFi networks, many other devices share the 2.4GHz band and can cause interference.

It is true to say that some VEXnet keys do go bad either from abuse (usually stress on the USB connector) or just due to component failure. We have discussed this on the forum in the past and, although I forget the exact numbers, the number is quite low, probably something like 2%.

The keys use the RT73 chipset from Ralink that was popular a few years ago, I think they were probably supplied by Tenda originally and I have used them with Tenda drivers under Windows XP. This is one way to detect broken keys but does not necessarily indicate they will work well with the VEX equipment.

There’s a little more background on the keys here.

Hi. I just spent a couple hours today tracking down a hairy vexnet problem with our new robot in preparation for a scrimmage Friday. I found a couple different problems.

First, the battery socket on the Cortex controller was loose. I found this by wiggling the battery plug and seeing the lights go briefly to 3 red lights. I fixed this by bending the sides of the round barrels in the socket inward with a teeny tiny jewelers screwdriver.

Then the robot would work for a while, but it would disconnect when it drove over the bump. This was quite repeatable. I eventually swapped out the Vexnet keys and found that we had two good ones and two that are sensitive to bumps.

I happen to be an electrical engineer (posting on my son’s account until my shiny new one is approved) so I took the keys apart and examined them under my microscope. I did not see any signs of loose or cracked solder joints. I did see that the plating was worn off of the USB contacts in the plugs.

I plan to order some new plugs from Digikey for a dollar each, and install them to see if this will repair the keys. If it works, I’ll post the info so that all those dead keys can be brought back to life.

Yes, let us know how you get on. Unfortunately similar repairs on other VEX components (potentiometers for example) have been ruled illegal for competition use, not sure how they would view the repair of VEXnet keys, probably best not to ask.

The key that I linked in the previous post had an intermittent connection on the main BGA, I could push on that component and get the key to work. Unfortunately there’s not much that can be done with that other than perhaps reflow.

Well as the teacher/coach/buyer of equipment for 20 vex teams over the last 7 years, I have seen most of the fail modes possible I think…

Basically the keys we have are not really designed for the high stress, high impact, metal cage, often WiFi rich, environment they have been put into. Added to all that is that schools are notorious for having wifi systems that don’t like our the way our keys talk to each other and those vexnet keys failure can be the single most frustrating thing most teams encounter.

I do have the luxury of swapping vex net keys as, we have about 50 at the start of every season, but some years we have faced a nearly 33 percent verified failure rate by the end of the year.

VEX has been really good about replacing defective keys in the past, but I don’t know how long they will continue to do this.

We have a way to test individual keys using a couple of laptops, and once we know they have failed we contact VEX. (I think Eli knows my name now)

Yes and you could repair some of them but that would definitely be something for the experienced technical person.

We only started tracking failure modes this year, I wonder if VEX has done so and would be willing to release that info?

In my experience, I have had a lot of faulty keys, but they’ve always been faulty from the start of use. For example, it might disconnect every so often, and I didn’t replace it because it was still early in the season and having connectivity wasn’t a high priority for me, since I just wanted to connect for a while to see if what I just built would run.

However, when I got a good key, it lasted. For example, the one I have on my robot and controller right now are the same keys I’ve had since my first competition all the way back in August. I programmed for quite a while with the key, and have my robot on a lot and practice with it a lot. This key has been abused quite a bit.

I don’t want to make myself seem like a careless person, and I take care of my stuff the best I can. Sometimes, accidents happen, and I drop my controller. It has been dropped around 2 or 3 times since August and everything still works fine with the connectivity. I have never had connection problems in any of my matches in the past competitions I’ve been in this year, which if I recall, is 3.