Static on the HDPE

[DanL]

Well if you don't get rid of the charge by running a ground to it, IS it the HDPE that creates the static electricity? What about doing some kind of ground-wire wire mesh type thing to be put under the hdpe? would that help it out any?

[sevisehda]

Elementary physics, the charge is on the outer surface of a insulator. The only way to remove it is by placing a conducting over the HDPE. As long as you keep your electronics away from the metal frame you should be safe. If your really that concerned you could always discharge the HDPE when you set your bot on the field.

[Al Skierkiewicz]

We are basically looking for other teams that are experiencing the static buildup. We are getting significant sparks when the robot drives from the HDPE onto the grid and occasionally the other way as well. We suspect that the static may be interfering with robot control but are still gathering data. We need to hear from teams that are having problems when they are running on a built ramp using the components listed in the FIRST docs. There is no doubt that the HDPE is charged as anyone who looks at it can tell it is attracting dust.

[Adam Y.]

IS it the HDPE that creates the static electricity?

Yes it is. Actually it is a combination of the rubber tires and the plastic on the top of the ramp.

[Josh Hambright]

we built the cheaper wooden ramp...and although we haven't run on the ramp a ton recently we have not seen this problem yet...but then again we are still finishing up the bot....

maybe placing a humidifier near the field would help by making the air less dry and more conductive to electricity.

[Solace]

it would have to be a REALLY REALLY BIG humidifier - I mean, at nationals, are they going to humidify the entire stadium?

[Josh Hambright]

it was just an idea... i mean i dont know what kind of space other people have for testing their bots but the room we use isn't very large and we could probably get away with an average sized humidifier...
but then again maybe the humidifier could have adverse effects on the robot.

[petek]

oneangrydwarf is correct that humidity would help dissipate the the charge. Which means that events in dry regions (like where winter RH is below 30%) will have more problems with this than warmer and damper areas.

Charge is built up when the robot's wheels rub against the HDPE and electrons are transfered between the materials' surfaces. Having a wood or metal support frame shouldn't make difference in the charge on the HDPE since it isn't a conductor. I think that if the wire mesh ramps were grounded they might take some of the charge off the robots though.

It's worth noting that our robots will pick up a charge on the carpet, too. I think we see more of a problem with the HDPE because, being a continuous surface, the robot makes more contact with it (than carpet) and therefore transfers more charge.

[ChrisH]

Originally posted by Solace
it would have to be a REALLY REALLY BIG humidifier - I mean, at nationals, are they going to humidify the entire stadium?

I don't think humidifying a stadium in Houston will exactly be a problem. Keeping it from raining inside will be more of an issue.

I remember a quote from somewhere "Air Conditioning - it made Dallas livable and Houston possible"

[petek]

Looks like FIRST has heard of this problem (From Team Update 16):

"In Team Update #6, FIRST allowed teams to connect their custom circuit(s) to the
programming port on the Robot Controller. Unrelated to this, there have been reports of
some static electricity discharges on the ramp / field. TEAMS SHOULD BE CAUTIONED
THAT PIN 4 OF THE PROGRAMMING PORT IS RESET. Teams that connect their
custom circuit(s) to the programming port have the ?potential? to initiate ?reset? by a static
discharge, which may result in unknown actions by your robot."

Ah the joys of ESD management.

[Dave Flowerday]

Originally posted by petek
Looks like FIRST has heard of this problem (From Team Update 16):

Yeah, they heard it from us. We told them that we found that the reset pin (pin 4) on the RC is very sensitive (we've seen our RC get into a constant reset situation from just having an unterminated serial cable connected to it - it acts like an antenna and picks up interference). I don't know if they knew this or not but after discovering this our team is really curious how many unexplained robot resets over the years were due to this very sensitive pin remaining unterminated on everyone's robot during competition...

Unfortunately they didn't answer our question at all - they just told us the same information that we had sent to them! Oh well, I guess they don't much care about the static buildup on the HDPE. Judging by the responses here, few other teams seem to be having issues with it, so I guess we're just out of luck.

FYI, we were doing more investigation of this issue tonight and found that by taking a big wire and holding it to the metal grate and then passing the other end over the HDPE will generate tons of little sparks.

I predict that there will be people getting nasty shocks while handling robots on the HDPE after the match, especially at the Chicago regional (since that's where we're located and the weather is nice and dry around here). If two robots get in a shoving match on the HDPE and start spinning their rubber wheels on it, watch out!

[petek]

Dave,

Sounds like we'll need ground straps to clip on the robots before we (or the officials) touch them! They do that with airplanes, so we're in good company.

I like the documentation that Innovation First provides on the pin 4 reset input circuitry: a black box labeled "reset circuitry". Do you know if it is pulled up or just an open logic input?

Well, I guess you could say that FIRST is presenting us with a real-world engineering problem by making the platform non-conductive. I'm sure that people in the material-handling world have to deal with this daily.

Pete

[Marc P.]

We've not experienced large discharges while moving on or about the HDPE, but we have experienced rather nasty shocks after it returns to the ground and we attempt to tweak something. I know there are some anti-static sprays around, we used to use them at school in our carpeted computer lab, so would any of them help if sprayed on the wheels or the HDPE itself? What if the HDPE were either charged or discharged between matches to match whatever the charge of the robots might be? e.g. rub it down with a silk cloth before each match, or wipe it off with a wet paper towel, or anything to at least attempt to equalize the charge? I noticed no shocks at all while handling the robot while it span it's tires on the HDPE, but that may be because we washed the HDPE shortly before, and although it was dry, it was mopped up pretty good with water.

Any thoughts?

[ChrisA]

Have a team member slide around on the HDPE and then have them touch another team member. We found that this seems to transfer some nice shocks. It's also quite a bit of fun.

[Dick Linn]

Would it be at all useful to add a piece of solder wick (braided copper wire used to remove solder - available at Radio Shack) to the chassis, connected to the metal robot frame via a 1 MegaOhm or so resistor, just to limit inrush current? That or connect a Varistor, Transorb (zener), gas tube or similar device? Afrer all, it's not the voltage, it's the current that causes the real damage.

Ask the guys that routinely service the high-voltage transmission lines from a helicopter. (Check out http://www.haverfield.com/) I don't know if they grab the 765,000 volt lines or not, but they do get ahold of some pretty high voltage lines, like in excess of 250 KV ( and I understand it smarts a bit).

Grounding and surge suppression is an art in and of itself.