This actually makes a lot of sense. All the ports that I’ve had blown are with longer cables. I’ll look into some sleeving , thank you.
The shield is probably a good idea. I like the “TVS” insert idea too for the present V5 brain ports. Could use these:
This is a good discussion on the shield issues:
Or Vex could use these in the future in place of the present RS485 drivers:
Of course, it’s all speculation, at this point, they may have already done that, don’t know.
From an EP point of view - if you are going to use anti-static products on your robot, please notify the EP and Head Referee. Use the product correctly. Products that leave residue on the fields are likely to be be forbidden. So good idea to test on your field tiles before damaging your host tiles.
As for other functional electrostatic mitigation technologies, please post to the Official Q&A before bring such solutions to competition.
I’ve taken some more internal pictures of the V5 brain and the RS-485 drivers are SN65HVD1782. SN65HVD178x datasheet says that it is rated up to 70v for transient voltage pulse and up to 16kV for ESD, but it says nothing about maximum current or power dissipation in the event of ESD.
SM712 chip, that you have recommended, is rated at 19A current pulse and 600W power dissipation for ESD of up to 30kV. SM712 datasheet says that it has bi-directional asymmetric TVS diodes (+12/-7v) specifically designed for RS-485. However, it is a bit pricey at $0.87 per port for 2 channel device.
The cheapest TVS alternative for non-volume buying seem to be 4-channel TVS array NUP4102XV6T1G for about $0.24 per port. But it is rated only at 3A, 75W, and 16kV.
Another alternative is SMDA15LCC 4-channel TVS array which offers 300W of power dissipation for an ESD event at a cost of $0.30 per port. SMAxxLCC datasheet says it was designed for RS-422 which is electrically similar to RS-485, but it says nothing about peak current and voltage rating for ESD protection.
SMDA15LCC seems like the best balanced solution in terms of cost per protection, but lack of max voltage rating for ESD protection bothers me.
Does anyone know if SMDA15LCC would be an acceptable option or SM712 is the only good choice?
I found the e-fuse FET part in your new pictures interesting. It only has 2kV protection and I assume there is one for each port? It’s all conjecture, maybe they protected it some other way, but I am starting to vote for it getting blown only because the present 485 driver has as least some fair ESD protection.
I’d like to know why after years of combating issues with ESD with the last generation why:
A. V5 wasn’t designed with this in mind and then thoroughly tested.
B. The Field tiles get changed.
Would a different material in the floor tile make a difference? Like rubber tiles that you find in weight rooms instead of the playroom foam tiles that we currently use.
Or would the rubber tiles make no difference and we’d experience the same issue?
The harder rubber interlocking tiles are over twice as costly as the foam, without finding custom blue and red ones somehow: https://www.uline.com/BL_2023/Rubber-Gym-Tiles
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.
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.
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.
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”