possible solution to the static problem

[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