V5 brain ports break continually

VEX V5 Technical Support
#95

I know the sign has gotten a lot of attention but it seems like there is actually some legitimacy to it. A lot of commonly touched statues etc at Disneyland apparently have unsafe levels of lead.


Anyhow, this doesn’t really matter, I was looking at the wrong product and the antistatic that Vex recommended does not, in fact, cause cancer. And for the most part I totally agree that Prop 65 is silly :slight_smile:

Nice sensationalist rant :slight_smile:

If you want to continue this lovely conversation, why don’t you DM me so this thread doesn’t get derailed any further.

#96

This is an update on the V5 Brain port issue. One of the team that had seven of their ports died on them within two competitions had a new Brain replaced. The new Brain were upgraded to latest firmware (v1.03). Regarding DRow’s post about using anti static on the wheels, the team did put on anti static on all four wheels on their robot for today’s competition. Granted that they didn’t use the exact same anti static that VEX recommended (Heavy Duty Staticide product) but they did apply anti static spray on their robot wheels before the competition.

Anyway, today’s competition, they had one port that was connected to the lift (about two feet long wire) died on them. However, this port isn’t completely dead like the other seven ports that died on them earlier that was on different Brain. This new half dead port still recognizes the motor being plugged in but it doesn’t generate enough power to move the motor. The red light on the motor port connector kept on blinking red instead of solid red.

I have ordered Heavy Duty Staticide product and should be here by Friday. I will have the kids apply the Staticide onto all their robot wheels for next week’s competition. I will update the results after next week’s competition.

#97

@KMonkeys
Good to hear your update. Just wondering, however, are you applying the Anti-static spray product to the wheels on the robot itself, because you are not permitted to spray it on the competition tiles? Also will it work with all the standard VEX wheels, or is there a particular procedure for each of the wheels?

#98

The kids spray the anti static onto the wheels on the robot itself because there is no guarantee that the EP spay any antic static onto the field. They have informed me that certain competitions have more static than others. So to be safe, the kids are trying to avoid having dead port issues, especially during the competition.

#99

Clever!

A team in my region was having some issues with static in SS, so they attached a cut and frayed extension wire to their chassis, and they grounded the other end. I have no idea if that is legal or effective, but they were convinced it was both. Maybe some combination of these two techniques would work the best?

#100

@DRow cannot say that static is killing the ports on the V5 brains.

First, I think, they are not 100% sure what is the exact mechanism. There is always some level of static in the air this time of the year, but ports are not all dying as soon as you put the robot out on the field - there is something else that is triggering ESD events. It could be wheels or flywheels generating extra charge as they move, it could be long wires accumulating surface charge, or it could be intermittent connectivity in the ports, …

It would have been nice if V5 brains had dedicated ESD protection circuitry, but they don’t and without knowledge how exactly ports are killed it is not clear what we could do to protect them.

The second reason is that once you admit that V5 brains are inadequately protected from ESD, then the next logical question would be: what about recall? And that is hardly possible, because you either need to issue the fix (which may be too long to produce, too costly, or both) or you need to reverse V5 transaction, which is difficult, because you could refund the money but reuniting teams with cortex hardware is hard.

For example, one way to protect the ports, without redesigning V5 brains, would be to insert surge protector between V5 ports and motors. Each having TVS devices and redundant ground connections to V5 brain ground. That would take time to design and manufacture and will add to the costs.

If that is the case, issuing anti-static recommendation to teams and EPs is perfectly reasonable thing to do, because it could be implemented quickly and doesn’t tie up any additional VEX resources. It has a potential to save the season for any team that got static vulnerable V5 brain on their hands.

Before VEX issued this recommendation I was researching a way to protect V5 from the team’s side. Making your own TVS protector is both not VRC legal and would be beyond the skill set of an average team.

If static charge accumulation on the fields is reduced by the spray and TVS port protection is not possible, then the next best line of defense might be to shield the wires and tie electrical ground of the V5 brain to all metal subsystems of the robot. Protecting wires is legal.

I found several products that might be able to achieve such task:

Flexo Anti-Stat
Flexo Conductive Braided Sleeving
Flexo® Chrome Expandable Braided Sleeving

Assuming average V5 robot needs about 16" of cables, then it will cost $20-$30 to protect it, depending on the supplier.

My questions to the mentors who has experience protecting electronics from ESD are:

Do you think this will work? Do you think it is a good idea to invest into one of these products as an insurance policy to protect V5 brains?

1 Like
Two Dead Ports In 1 Day
V5 port burnout
Static Build Up Causing Motors to Burnout
#101

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.

#102

The shield is probably a good idea. I like the “TVS” insert idea too for the present V5 brain ports. Could use these:

https://www.semtech.com/products/circuit-protection/rs485/sm712

This is a good discussion on the shield issues:

http://www.ti.com/lit/an/slla292a/slla292a.pdf

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.

#103

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.

#104

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.

https://www.digikey.com/product-detail/en/littelfuse-inc/SM712-02HTG/F6450CT-ND/5019610

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.

https://www.digikey.com/product-detail/en/on-semiconductor/NUP4102XV6T1G/NUP4102XV6T1GOSCT-ND/2122070

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.

https://www.digikey.com/product-detail/en/smc-diode-solutions/SMDA15LCCTR/1655-2010-1-ND/9562577

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?

V5 Brains out of stock
#105

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.

#106

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.

#107

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

#108

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…

#109

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.

#110

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.

#111

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.

#112

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.

#113

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.

Broken V5 Ports... and How to Fix Them!
V5 Brains out of stock
#114

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.