V5 brain ports break continually

Any solution would not be as low cost as these tiles, But I for one would gladly re-invest if it meant that we no longer had to deal with this issue.

But it would require having enough product to sell to all the EP’s and we know how well product launches from this company generally go…

The rubber tiles wouldn’t involve a global resister shortage that has impacted the electronics. Would probably be an easier solution than solving the worldwide backlog for electronic components.

I would also gladly replace our tiles, which are due for replacement anyways.

It’s all conjecture right now, we don’t have any idea what is happening. VEX will though, I would assume, soon, since parts can be analyzed by the manufacturer to see what failure mode was induced. But, with info coming from all different angles, it could be all sorts of things. If it is ESD, I would expect it to get worse as we get into the cold/dry season, let’s see.

I have gotten 1-2 ports to not run motors on a first-time startup, but they worked after restarting the V5 Brain. Other than that, I have never personally broken a V5 Brain port, even after following instructions on splicing cables correctly for custom-made cables. On another note, as a suggestion, If you have any spare time, I think it may be useful to open up your V5 brain and look for any deformities in the chip. Also, regardless if defomed or not, you can still post a picture of the chip’s front and back and see if anyone else can notice a deformity, such as soldering over or across multiple wires.

Having seen the inside of a dead V5 motor, I sincerely doubt the vast majority of cases of V5 issues will come with any obvious visible damage. Testing with a multimeter/oscilloscope would probably be the only solution in such cases.

Plus, most people probably won’t be willing to take apart their precious V5 hardware.

According to many posters the motors connected to the dead ports still have red status lights but do not communicate with the brain, which suggests that they still have power while RS-485 is dead. I would expect power line connected to eFuse to have more capacitance (filter caps) and much better chance to survive ESD than the low-capacitance data lines.

I dug deeper into RS-485 driver SN65HVD1782 datasheet and it states that when in active HI state the damage may occur with as little as 30V voltage on the inputs and, also, page 21 recommends installing SMBJ43CA TVS diodes to protect input lines, which I don’t see on V5’s pcb.

Bi-directional SMBJ43CA and SMBJ43CD devices could be bought for as little as $0.11 in large quantities or for $0.44 for non-volume orders. This would be similar to the cost of SM712 ($0.87) to protect 2 channels on one RS-485 port.

https://www.digikey.com/products/en/circuit-protection/tvs-diodes/144?FV=1b14006b%2Cffe00090&quantity=0&ColumnSort=1000011&page=1&stock=1&k=SMBJ43&pageSize=100&pkeyword=SMBJ43

There is one local team that has already blown 10 ports on their V5. All with cap flipper motor (on the end of DR4B) connected with a long pre-made cable. Apparently their robot and/or their practice field has something special that makes ESD strikes worse.

I bought several SM712 earlier today and will try to make a line inserts to see if they could be effective to protect their ports before they RMA their V5 brain.

Maybe, I was wondering if after an ESD event they started to fault as power got drawn, so could never really boot up. But, we have no schematics and I have no V5 hardware, so it’s just discussion.

I like the insert idea, especially if they are prone to issues on their field. Would help understand it. But, I would imagine VEX already knows what it is and maybe working on it since all they would need to do is send some chips to the manufacturer to get decapped and they will tell them pretty quickly what killed it. Wondering how many units are having the issue at this point? Probably low from a % standpoint in that academic is a big part of their sales and I would imagine academic may not see this issue since they aren’t on the foam fields. Also interesting that this wasn’t seen in beta, but that was during the more humid summer months so if it is ESD, that may have had no trigger.

Yep. Vex quality right here, had the same problem. Best to just get a new wire or something.

I have my theory about the most likely sequence of events that lead to this, but I would rather not share it, because I don’t know what really happened.

Statistically this type of issues often occurs due to the lack of communication between parties involved in the product development. Datasheet for RS-485 driver states that:

Whoever made decision not to add TVS devices to V5 brains apparently assumed that it is consumer grade equipment that is not exposed to industrial level hazards.

However, there was plenty of anecdotal evidence that ESD is quite frequent phenomenon on the VRC fields.

https://vexforum.com/t/esd-my-thoughts/23332/1


https://vexforum.com/t/static-electricity-ruining-brains/38143/1

Even if Cortex IME unreliability, long suspected to be caused by ESD, was never resolved and mostly forgotten, ESD was brought up again between January and April earlier this year while discussing VexNet resets. VEX engineers might have concluded that VexNet resets were due to the bad competition ports abused by the students, but the ESD theory was still front and center for weeks on various online platforms.

https://vexforum.com/t/field-control-a-technical-analysis/25651/1

Back then @Paul Copioli said that they have an ESD gun in the lab.

Did anyone try to fire it at a realistic V5 robot as it was driving around the field interacting with the game objects?

Was there enough time to make another revision to V5’s PCB that would include ESD protection (that could cost as little as $2 per V5 brain)?

In any case, rather than finding whom to blame, it is more important to see what could be done now to avoid killing even more V5 ports.

Anti-static spray is a very good first step to address the highest risk environments - on the competition fields but, I feel, another line of defense would be warranted. We will try to run some experiments locally to test effectiveness of various protection methods on a few robots that are already partially damaged and need to be RMA’d anyways.

One piece of data that would be nice to have would be to know if the same RS485 transceivers are used the motors?

Interesting to know if ESD is affecting motor ports, is it killing motors? The motor should be acting the same in either case of failure, brain or motor, transceivers.

Again, just conjecture, but interesting speculative conversations.

They appear to be the same, as seen in my V5 pictures thread. Will try to get a better quality picture.

Indeed they are the same. I will be deep-diving into the circuitry of the motors, complete with high resolution images, soon (after finals).

They should rename their robot “St. Elmos Fire”

Just had port 8 die on my brain… sigh
900mm stock cable, no visible damage to the cable or either port. Cable was not zip tied at all and was really loose (didn’t ever get snagged). Motor was barely ever used, and was not being used at all when port died (was in active braking move though, but was not binding up against anything).

Edit: And now the motor on port 6 has randomly reversed itself!? A reboot fixed the issue, for now, but what the heck?

In my opinion, anti-static spray is a mistake. It gums up the fields and doesn’t even do that good of a job at reducing static for extended periods of time. The correct solution is to electrically ground the fields. Since the Virginia State Championship switched to electrically grounded fields mid-event two years ago, there have not been any issues at that event or any other events that I know of that electrically ground their fields.

-Mike

I agree. I’m just scratching my head that anyone would consider anything different. This works like a champ and has zero impact on robot performance. This is fundamentally the correct way to eliminate static since potential voltage can accumulate on ungrounded surfaces.

how did they do that?

I think with cords like this:

With a cord similar to this one (the green wire is attached to the perimeter via ring terminal where the monitor attaches). This particular cord also serves as a monitor extension cord.
VEXGroundingCord.jpg

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If I have time today I’ll find a photo of the grounding wire they use, which is located on the back of the monitor where the Pis sit.

I’ll find a photo for it.

The only issues with static and disconnects in VA, conveniently came at the tournament that doesn’t use standard equipment.