Static electricity: quantitative measurement & prevention

VEX V5 Technical Support
1

There are many threads on static issues: complaints, notes on static spray, anti static tiles, dead motors, dead brain ports, ESD brain protection, and so on.

What I have NOT seen (and if there’s a thread please point me to it) is an actual measurement of the static levels involved, where they are actually generated from, how they build up w/o discharging, and building practices to prevent all of the above.

I’ve sent a few PM back and forth with a member here regarding these issues. They pointed out that arm/clamp/lift/mechanism motors tend to die much more often than chassis/wheel motors.

I don’t have enough exposure to say one way or the other… I think that my experience is similar. So, what say you all? Are motor/brain port failures heavily biased towards NON-chassis instances?

Also, I found a static meter on Amazon. Has anyone actually taken readings on bots? I would be very interested to see some hard data.

Finally, I recently read that some of the static was allowed to build by drive wheels generating it and the drive axles being isolated from the frame via the plastic flat bearings. I have made my teams put a metal shaft locker between the motor and the 1x2/1x3 it’s mounted to. A. this is a good place for a locker and B. This allows the shaft to be electrically conductive, through the locker, into the chassis.

If this is accurate, that isolated motors are susceptible, then most lifts (that use flat bearings) would be in that group. I would like to see a lift, with and without grounding, be measured via a static meter.

Maybe, with some careful analysis and specific build practices, we can put an end to dead electronics.

Let the discussion begin!

2

something I talked with @turbodog about was the potential to now legally be able to use copper (or other highly conductive metal) “string” to ground parts of the robot together.
https://www.robotevents.com/VRC/2021-2022/QA/861

You could very easily link parts of a lift or other robot appendages together with this “string” so that static would travel through it instead of the cables. This is, of course, based on my very limited understanding that the cause of ESD damage to the brain is when static electricity causes a surge to run from one part of the robot to another, taking the cable as the path of least resistance. So offering an even better path for the electricity to flow could drastically reduce the issue, if this is indeed how it works.

3

You could use graphite… it’s allowable as a dry lubricant and will conduct enough to link parts together.

But I really want to know which locations motors/ports are failing in and if anyone’s actually used a charge meter.

4

Who would like to take one for the team and possibly(likely) damage expensive, difficult to acquire equipment, and in high demand. I really do think that it could be a very fun experiment and the data would be interesting at the least and useful in preventing electronics failures at best.

5

I don’t think it would come to that. You could run around for 30 seconds and measure the static charge. Then ground the lift and try again.

6

That’s a great idea! I think it could be an excellent experiment to put several DIY Electroscopes onto the robot and stop at regular intervals to take the readings.

electroscope

I am pretty sure that you can build them from the supplies available at the local hobby store: i.e. golden leaf foil or tinsels, copper wire or brass tube, small glass bottles with cork or other insulating plug.

diy-electroscope

They could even be put on competition robots as perfectly VRC legal decorations.

7

I’ve got a bin full of bad motor boards that I’ve been meaning to test with (the ports still work but they don’t spin the motors). From my experience, 5mm ferrite cores clipped within a few inches on the brain end of the cable are very effective at reducing ESD damage on boards. I have only ever had one port die when using them in the last three years and that was on the absolute worst field I have ever seen in terms of static (significantly worse than 2013 nationals). In that time I have fried at lest four motors and over a dozen ports from static when I wasn’t using ferrite cores.

I have done some very unscientific testing which involved shocking myself repeatedly. I found that when I gave myself a static charge and then grounded myself through a V5 cable that had a ferrite core clipped on the end, I never felt a shock, but I also no longer had a static charge (didn’t get sapped when touching ground afterwards directly). I also tested the cable with no ferrite core, which shocked me every time. I repeated the experiment several times with the same results. I am led to believe that the ferrite cores help dissipate most of the ESD into heat, since it is technically a high frequency signal which they are designed to block.

I personally think they fall under R18 point F:

Commercially available items used solely for bundling or wrapping of 2-wire, 3-wire, 4-wire, or V5
Smart Cables, and pneumatic tubing are allowed. These items must solely be used for the purposes
of cable protection, organization, or management. This includes but is not limited to electrical tape,
cable carrier, cable track, etc. It is up to inspectors to determine whether a component is serving a
function beyond protecting and managing cables.

I would argue they protect cables from ESD. They do not require any modification to the wires and can be removed quickly and easily if needed (although I have never had to remove them at a tournament).

8

interesting take, I like this idea. I would agree with you that they could very well fall under cable protection, but whether the gdc would is beyond me.

9

I can’t see the argument for cable protection standing unless the static was damaging the cables themselves.

Note the word “solely” in the rules.

We aren’t replacing bad cables when things fail.

10

I think it’s in a bit of a grey area. One way to use them they might be slightly less grey is if you used a larger ferrite core and put two cables in it, since that would then be bundling.

If they don’t fall under R18, they should still fall under R13 as non-functional decoration since they do not serve any functions that significantly effect robot performance during a match. I’ve never had a port die during a match since from my experience that level of ESD usually only happens when someone touches the robot.

R13

Decorations are allowed. Teams may add non-functional decorations, provided that they do not affect Robot performance in any significant way or affect the outcome of the Match. These decorations must be in the spirit of the competition. Inspectors will have final say in what is considered “non-functional”. Unless otherwise specified below, non-functional decorations are governed by all standard Robot rules.

In order to be “non-functional,” any guards, decals, or other decorations must be backed by legal
materials that provide the same functionality. For example, if your Robot has a giant decal that prevents Scoring Objects from falling out of the Robot, the decal must be backed by VEX material that would also prevent the Scoring Objects from falling out.

a. Anodizing and painting of parts is considered a legal nonfunctional decoration.
b. Small cameras are permitted as non-functional decorations, provided that any transmitting functions or wireless communications are disabled. Unusually large cameras being used as ballast are not permitted.
c. VEX electronics may not be used as non-functional decorations.
d. Decorations that visually mimic field elements, or could otherwise interfere with an opponent’s Vision Sensor, are considered functional and are not permitted. This includes lights, such as the VEX Flashlight. The Inspector and Head Referee will make the final decision on whether a given decoration or mechanism violates this rule.
e. Internal power sources (e.g. for a small blinking light) are permitted, provided that no other rules are violated and this source only provides power to the non-functional decoration (e.g. does not directly or indirectly influence any functional portions of the Robot).
f. Decorations which provide feedback to the Robot (e.g. by influencing legal sensors) would be considered “functional”, and are not permitted.
g. Decorations which provide visual feedback to Drive Team Members (e.g. decorative lighting) are permitted, provided that they do not violate any other rules and serve no other function (e.g. structural support).

11

If I were inspecting bots, the ferrite core would be kicked out.

That said… and this really goes to the core of my reason for posting… one could argue that the cores are protecting the wire if the static charge is entering the wire from the chassis. If so, then the core is protecting the wire against unsafe and out of spec voltages.

But you would need to show, or have it be common knowledge, the source of the static charge, hence my posting.

12

Amazon has a nice static meter for around $215. Anyone want to go in?

13

legality aside, is there any real excuse the gdc has for these not to be legal? it’s an 8 dollar product that seems to have the potential (I say potential because I think further testing is needed to confirm that they really do significantly help the issue, but @Bob132 's experiments sound very promising) to save hundreds of dollars of equipment.

Ideally, adequate esd protection would have been built in to the system to begin with, but it wasn’t. Legalizing anti-static spray and making anti-static tiles were good moves to help reduce the problem, and they show that the issue is at least acknowledged. These, coupled by using any sort of 3rd party solution you’d like is a way to mitigate the issue during practice, but currently there is almost nothing a team can legally do apart from grounding parts of their robot together in competition, where the integrity of ports can make or break a match. I think a q&a on the legality of these could be a great opportunity for the gdc to firmly legalize a form of ESD protection legal in competition in a way that’s easily accessible to everyone.

I’d like to perform some further testing though, which might be difficult to do quantitatively considering it sounds like they don’t actually prevent the buildup of charge, they just prevent the adverse effects of it surging through the cables.

14

Reason for not legal??? Not that I can think of. They are cheap and easily available.

You can run plastic cable sheathing to protect wiring against random foreseeable damage during a match. Maybe the snap on cores could be viewed in the same way, but really a ruling by the powers that be is needed. And it might be a fluke…

Edit:

Maybe classify as ‘general electronics protection’ from competition/driving damage.

And also, I’ve got a static meter on order from Amazon.

15

In that situation they can be removed from all the wires in just a couple minutes and the robot can be re-inspected. Even if teams can only use them during practice, they are still very useful.

Yeah my understanding is that ferrite cores do not prevent static buildup, just dampen the discharge.

If you are planning on using that static meter to perform some more scientific testing (i.e., well documented with lots of pictures), I’d be happy to send you some motor boards and discuss the test procedures.

16

That seems to be the case. I know that several FTC teams have started to use them after the immense static issues at the 2018 Detroit World Championships which caused 11115 to lose due to static-related disconnect issues (in one match LAN Bros disconnected immediately after autonomous and sat there like a dead duck in the water). As a matter of fact, the winning alliance’s robots switched to ferrite cables as soon as they saw how much static was on the Ford Fields.

Now as to why they aren’t legal in VRC, that’s beyond me. Perhaps the GDC thinks that the static issue isn’t as big as we’ve chalked it up to be, or perhaps VEX is creating their own solution to the problem…

17

I’m going to do pretty much what’s been detailed so far.

  1. Get some baseline readings on the field itself to get familiar with the meter.
  2. Drive a bare chassis around, take some readings.
  3. Drive a 4bar bot around, take readings.
  4. Use ground strap on 4bar, take readings.

In short, try to capture enough data till a pattern appears. Our field has the old ‘static-producing’ tiles. It HAS been sprayed with anti-static spray though. But I figure I can still get some data/results to appear.

To note… the fields themselves might need grounding. Ours is on a wooden platform and wood is a decent insulator, especially with the “plastic” wheels that the casters have (we can roll the field around).

18

I think most fields at tournaments are not grounded. Theoretically having a grounded wall could increase ESD when contacting the perimeter, but I could also see it helping to discharge the mats around the edges.

Would you be interested in testing the effectiveness of ferrite cores? If you aren’t then I’ll try to do it when I can find time. I would probably end up using the DIY method for measuring static @technik3k linked instead of buying my own meter. I also might fire up the old Van De Graaff to get more consistent ESD for testing.

19

Don’t know right now. Can’t see how to test the core using the meter. Looks like the meter’s shipping from China so it will be a week or two before I get it.

20

A few of the practice fields at WPI weren’t even anti-static tiles, and I would get shocked every time I touched the bot. Also, at Weston, we ended up blowing a port because of their practice field, which were also not anti-static tiles. This resulted in us losing a few matches cause we couldn’t figure out why our code wasn’t running our ring mech at all.