possible solution to the static problem

[writchie]

Apparently a beaded brass drag chain is not prohibited:

http://forums.usfirst.org/showthread.php?t=12284

But a static discharge wick on the other hand is expressly prohibited:

http://forums.usfirst.org/showthread.php?t=12228

Go figure. I can't wait to see the engineering explanation for this (or has marketing taken over )

We will be installing a drag chain based on this ruling. It appears to be the only pro-active static mitigation method permitted on the field (other than dealing with van de graff generators on the Robots).

Chain has the advantage of guaranteed contact with the floor and the disadvantage that a corroded link could cause a high resistance in the discharge path. Movement should mitigate that and the charge can be passed along bead to bead, not to mention that the chains will be new.

The static wick has the advantage of guaranteed continuity but the possibility of becoming no longer in constant contact with the floor.

All in all, I think 79's chain solution is probably the best.

Unfortunately, protecting your own Robot in this manner may not protect you on the field when you contact another robot. If a large charge is allowed to build up on one robot, the discharge transient could possibly end up resetting either cRIO.

Also, it may be a good idea to insure that all power and signal leads have as great a distance from bare chassis metal (and charge generating materials) as possible. Normally, we only need to worry about short circuits. In the high ESD environment, we also have to worry about jumping the spark gap. A 10K charge can cross a 3MM gap.

BTW, it doesn't matter to 75% of the teams what solution is in place after week 6.

IMHO a quick fix that should be explored is to modify the trailers. There are only 6 trailers on the field and 6 drag chains are relatively easy to install. This is an easy fix to install, easy to test, and doesn't involve teams having to scramble to do something. It can be done during practice matches. Split the regionals, put chains on half and not on the other half and then correlate resets, chains, and humidity. If it makes things worse, it will do that for only half of the practice rounds. If it makes things better, it will do that for half of the practice rounds. (I'm ignoring the DS issues - they are a different matter).

The good news is that it looks like the cRIO is proving to be solid and the worst case result is a reset. There is probably no way to do better than that with everything floating. I'm extremely impressed by the cRIO. Great Job NI! and thank you for supporting FIRST.

[Trent B]

Originally Posted by writchie

Apparently a beaded brass drag chain is not prohibited:

http://forums.usfirst.org/showthread.php?t=12284

But a static discharge wick on the other hand is expressly prohibited:

http://forums.usfirst.org/showthread.php?t=12228

Go figure. I can't wait to see the engineering explanation for this (or has marketing taken over )

If you read a little more into it, you will notice the chain group was just using chain attached to frame. While the static discharge wick also asked about the use of bleed resistors to ground the frame. We know electrical connections to the frame are prohibited, but I think static wicks attached in a manner similar to the drag chain would be acceptable by the GDC.

[EricVanWyk]

Originally Posted by Trent B

If you read a little more into it, you will notice the chain group was just using chain attached to frame. While the static discharge wick also asked about the use of bleed resistors to ground the frame. We know electrical connections to the frame are prohibited, but I think static wicks attached in a manner similar to the drag chain would be acceptable by the GDC.

Thats how I read it.

Chain attached to frame only = good.
Static wicks attached to control electronics AND frame = bad.

Still better to ask the specific question of "Wicks attached to frame only = good?"

[writchie]

Originally Posted by EricVanWyk

Thats how I read it.

Chain attached to frame only = good.
Static wicks attached to control electronics AND frame = bad.

Still better to ask the specific question of "Wicks attached to frame only = good?"

Teenager: Dad, May I use the car?

Teenager: And may I have the $20 bill on the kitchen counter?

Dad: No and No.

Where I come from this means NO, you cannot use the car and NO, you cannot have the 20 bucks. It does not mean the $20 is yours but you can't use the car.

I am not arguing the GDC's intent. I certainlyl have no way of knowing their intent other than by the words they write. I am just pointing out that words have meaning. There is no reasonable engineering basis I can think of why a beaded chain would be allowed and a static wick prohibited just like there is no way under the rules of English to read No and No to mean No and Yes.

It's far less effort to just buy the brass chain. Anyway, the GDC seems to have determined that there are no actual static problem that a spray bottle won't solve.

[Jim E]

This is an interesting discussion.
FIRST wants feedback on how our system are performing. The Northern-Climates are expected to have a harder time due to the drop in humidity in the Winter months.

I have dabbled in ESD measurements and the verticle ESD wave occurring across the conductive (ground) playing surface(ice rink) can be pretty large too. This wave requires intense engineering to solve for electronic devices.

Please provide feedback to them, good or bad. Describe how your components are mounted in detail. Wood or Lexan. How do you isolate it from the chassis.
if they are looking for the best way to mount a CRio in space, maybe your design will be selected.

[Al Skierkiewicz]

Originally Posted by writchie

Apparently a beaded brass drag chain is not prohibited:

We will be installing a drag chain based on this ruling. It appears to be the only pro-active static mitigation method permitted on the field (other than dealing with van de graff generators on the Robots).

Chain has the advantage of guaranteed contact with the floor and the disadvantage that a corroded link could cause a high resistance in the discharge path.

The regolith is also nonconductive. I would put it's voltage standoff rating in the tens of Kv range or better. Maybe I am missing something here, but I don't see how a drag chain could have any additional effect. When you use a drag chain over concrete, the material is conductive to some extent and likewise for carpet depending on the humidity and moisture content of the materials. The regolith is adverse to moisture absoption so it's electrical properties should not change over a weekend.

[EricVanWyk]

Originally Posted by Al Skierkiewicz

The regolith is also nonconductive. I would put it's voltage standoff rating in the tens of Kv range or better. Maybe I am missing something here, but I don't see how a drag chain could have any additional effect. When you use a drag chain over concrete, the material is conductive to some extent and likewise for carpet depending on the humidity and moisture content of the materials. The regolith is adverse to moisture absoption so it's electrical properties should not change over a weekend.

Al -

I had the exact same thoughts 24 hours ago. However, some time with the ESD gun made me revise my thinking.

Think of the regolith as an array of isolated capacitors. As you drive across the surface, you steal charge from these capacitors. Dragging the chain gives it back. If your only static source is the rover wheel / regolith interaction, this should do a good bit to improve things, especially if your chain sweeps the same area your wheels do.

If your charge imbalance comes from your ball manipulation, you won't be able to directly return the charge by this method. However, you will be able to spread the effect over the area you sweep.

Additionally, the capacitors are actually connected with very high value resistors. These will allow the charge imbalance to slowly spread over the surface.

[Al Skierkiewicz]

Erik,
Since the gun is the source, what did tests did you perform that led you to this conclusion? If the floor can be modeled as a series of capacitors, what is the other plate of the capacitor and why would a 28x38 robot frame not also be part of the capacitive equivalent circuit? I can agree with the series resistor part, but at the insulation level of fiberglass and gel coating and the material's inability to absorb moisture, the series resistance must be pretty high. i.e.>100Mohm. I have done a cursory check on electrical characteristics of this material and so far I have not found any. However, looking at the gel coating and polymer base material as likely being similar electrical properties, I am guessing the surface resistivity to be in the 10^12 ohms/cm or higher. In putting all the reports together (and in the absence of better testing) I am guessing that the static is a condition of the carpet to FRP transition rather than the robot to FRP. If this is the case, then a drag chain will not be effective until the chain contacts the carpet at the field borders. Should this be the case, then chains should be effective if applied to multiple points on the exterior dimensions of the robot, to insure charge drains off prior to a robot to field border interaction.

[pitzoid]

Originally Posted by Al Skierkiewicz

If this is the case, then a drag chain will not be effective until the chain contacts the carpet at the field borders.

Al/Eric

While the chain idea may seem counter intuitive, I've have got PMs from multiple teams saying it worked. Like Eric eludes, the FRP is like a series of capacitors connected by high value resistors. I know some of these bots are building incredible potential by being isolated, running high speed ball manipulation devices like tornado and belt drives and then being completely insulated by at least 3" due to the 6" plastic wheel. So remember that spark gap is all attributable to voltage potential and distance, even if the FRP isn't "real" conductive, a huge potential on a bot could be bleed off. Either a bot is going to build enough potential to have the spark jump from their frame to the FRP floor (which is a scary voltage thought) or they are going to have enough potential to jump from when they get near the grounded arena boundary. I wouldn't be surprised if some of the spark gaps we're getting at the arena boundaries exceed 1-2", big EMPs. You know air isn't really conductive, but I've seen alot of lightening in my time It all comes down to the triboelectric series, anything we can do to encourage the static voltage potential to transfer will help the ESD/EMP effects.

[Al Skierkiewicz]

Bob,
I understand that if the problem is regolith to carpet and a team has a chain that contacts the carpet before they hit a field border, then it may work as the discharge path is carpet to robot. In looking at Bill's Blog and the suggestion that carpets be made wet at the field borders, there seems to be mounting evidence that the floor materials are the prime fault. When we walk out and set the robot on the playing field, it then becomes the same charge as the Regolith. As robots move about, the charge builds up constantly on all robots as the interface between the FRP and carpet gets exercised. I would like to see if an experiment consisting of wire under the FRP and across the carpet to the field border might work better than water on the carpet. 3M makes a nice product that is a copper foil with a conductive adhesive that could easily be added to the field and would not likely produce any serious change in game play. The tape is available in various widths and can be purchased from Digikey.

[David Brinza]

As I've previously mentioned in a related thread, an anti-static spray coating like ACL Staticide leaves a slightly conductive film on the surface of the regolith. It's available from McMaster-Carr (7090T37) in a 1-qt spray bottle, enough to treat an entire field. This product is designed to dissipate static charge on slick, non-porous, hard surfaces. If conductive copper tape were attached between the regolith and field boundary at a few locations around the field, the charge will have a path to bleed from the robots, down a chain, across the regolith, through the field structure, and finally to earth ground.

Perhaps someone can measure the change in coefficient of friction for regolith treated with Staticide. I suspect the change in friction would be quite small. The benefits of minimizing loss of comms, DS resets, replayed matches and even damage to electronics should offset a slight change in the playing surface.

[jerry w]

Originally Posted by Al Skierkiewicz

The regolith is also nonconductive. I would put it's voltage standoff rating in the tens of Kv range or better. Maybe I am missing something here, but I don't see how a drag chain could have any additional effect. When you use a drag chain over concrete, the material is conductive to some extent and likewise for carpet depending on the humidity and moisture content of the materials. The regolith is adverse to moisture absoption so it's electrical properties should not change over a weekend.

Let's not forget surface charges. As a material collects charge of a certain polarity, that charge spreads over the surface of the material. The chain brings the opposite charge down to the surface. This allows a restoration over time. Since the buildup occurs over time as well, we have an equalizing effect. The difference in charges will never become large.

Now that the trailers are using a drag chain, I would expect to see no large buildup on the playing field. However, the practice field remains a problem. The trailers on the practice field had no chain. Also, robots on this field have a tether cable attached. If charges are allowed to build, the driver station is subject to potential damage. an arc to the tether from robot frame is likely. the driver station has only minimal esd protection.

I have not heard credible evidence about cRIO damage. So far, there is evidence of only driver stations that have failed. I have seen and heard of only damage to driver stations and analog breakout modules. Other comments, here and elsewhere, have lumped the system failure as a cRIO failure. Please understand, i think WPI did a very good job of making a cRIO based system. it is simply not as rugged as the NI equipment.

(Also, spraying the wheels may work, but is against the rules. This lubricant changes the traction of the wheel.)

jerry

[writchie]

Originally Posted by writchie

IMHO a quick fix that should be explored is to modify the trailers. There are only 6 trailers on the field and 6 drag chains are relatively easy to install. This is an easy fix to install, easy to test, and doesn't involve teams having to scramble to do something. It can be done during practice matches. Split the regionals, put chains on half and not on the other half and then correlate resets, chains, and humidity. If it makes things worse, it will do that for only half of the practice rounds. If it makes things better, it will do that for half of the practice rounds. (I'm ignoring the DS issues - they are a different matter).

Neither static wicks nor drag chains were permitted by the inspectors at the Florida regional. I suggested to them, (and probably others made similar suggestions), that they consider drag chains on the trailers since that could remain completely under their control. Our drivers saw the chains on the trailers on Saturday.

I know that Team 2383 was having reset issues on Friday that disappeared on Saturday. They would reset every time they contacted a wall. This, however, could have been electrical rather than electrostatic.

I don't know if the "Trailer Drag Chains" have been tried at other regionals but it does appear that at least they do not make matters worse on the actual playing field, at least as far as Robot resets are concerned.

[AlexD744]

Originally Posted by writchie

Neither static wicks nor drag chains were permitted by the inspectors at the Florida regional. I suggested to them, (and probably others made similar suggestions), that they consider drag chains on the trailers since that could remain completely under their control. Our drivers saw the chains on the trailers on Saturday.

I know that Team 2383 was having reset issues on Friday that disappeared on Saturday. They would reset every time they contacted a wall. This, however, could have been electrical rather than electrostatic.

I don't know if the "Trailer Drag Chains" have been tried at other regionals but it does appear that at least they do not make matters worse on the actual playing field, at least as far as Robot resets are concerned.

I thought the drag chains worked really well for static at Florida. And reset isn't difficult if you have a list and each person does a specific job. For us coach and one drivers set up robot and trailer, the other driver set up the the control board and tethered BEFORE giving the other 2 the signal to turn on the robot and set autonomous. All the while our human player was taking his moon rocks to fill our robot's hopper. it was really smooth. Another thing to check is the radio ethernet cable. The programmers have to unplug it and sometimes forget to replug it.

[pitzoid]

Originally Posted by writchie

I don't know if the "Trailer Drag Chains" have been tried at other regionals

This was tested at FIRST last week and deployed to all week three regionals, the real test will be this coming weekend when there's another "ice rink" regional. There's weren't any week 3 ice rink regionals.