Static on the HDPE

[petek]

Wiping down the HDPE with a wet cloth could dissipate the charge on the surface - the water and the wiper (you) complete a circuit to ground (assuming the person is grounded). I'd think it might help if FIRST did that between matches. Might also improve traction since dust & stuff would get wiped off. I don't think FIRST would go for anti-static sprays, since they would leave a residue which might affect traction.

A ground strap attached to the robot which dragged on the ramp mesh would bleed the charge off the robot, again assuming the mesh is grounded. Even if the mesh isn't grounded, I don't think you'd get zapped, since you'd be standing on the mesh when you touched the robot.

Like Dick said, an art. Or magic... Which makes me wonder: we all know that electronics works because of smoke (let the smoke out and they stop working). So where does static electricity fit in? I haven't seen any smoke, but the discharges are audible. Does that mean that static electricty works on noise?

[Adam Y.]

Wiping down the HDPE with a wet cloth could dissipate the charge on the surface - the water and the wiper (you) complete a circuit to ground (assuming the person is grounded). I'd think it might help if FIRST did that between matches. Might also improve traction since dust & stuff would get wiped off. I don't think FIRST would go for anti-static sprays, since they would leave a residue which might affect traction.

That would work until the robots started driving up and down it then both the robot and the hdpe would have a charge again.

Does that mean that static electricty works on noise?

Errr what does that mean???? Im confused static electricity is totally unrelated to noise. The noise you hear is exactly what thunder is.

Afrer all, it's not the voltage, it's the current that causes the real damage.

Not true either. If you have an electronic component that is rated for 6volts and it gets 100volts from a static spark it is going to die on you.

[f22flyboy]

Quick and dirty fix:

Get a coat hangar

Before the match, discharge the HDPE by placing the hangar across the HDPE and the wire mesh.

After the match, place the hangar from the frame of your bot to the wire mesh.

This won't help static electricity built up during the match, but will minimize it and keep you from getting shocked when you pick up the bot.

Semi-related life experience:

I play volleyball. We play on a surface called sport court, which is a high density plastic. We also wear gum rubber soled shoes. As you can imagine there is quite a bit of static electricity. You get used to getting shocked by the floor every time you dive or touch a wall, but one unpleasant experience is getting your tongue shocked by water from the water fountain. It burns like heck and then your tongue goes numb for about 15 mins. So we have learned to discharge the water with a finger (or let someone else discharge it). This same lessons can be applied to robotics

[Dick Linn]

Originally posted by wysiswyg
That would work until the robots started driving up and down it then both the robot and the hdpe would have a charge again.
Errr what does that mean???? Im confused static electricity is totally unrelated to noise. The noise you hear is exactly what thunder is.
Not true either. If you have an electronic component that is rated for 6volts and it gets 100volts from a static spark it is going to die on you.

The voltage (potential) is what initiates the breakdown but it is the energy (voltage x current) or the current that melts things.

[Adam Y.]

I think your wrong though because static electricity is high voltage low low current. If it was the other way around then humans would be dropping dead left and right because it only takes 1amp to stop a human heart. Some electronics are more sensitive to sudden voltage spikes then others are.

[Josh Hambright]

i wonder if first would mind if you just grounded the ramp yourself with the coathanger idea before the match started....
as far as having a coat hanger or the solder braid coming off your robot, i would be afraid of violating one of the rules like no metal in contact with carpet or no penetrating the surface of the mesh.

Static electricity can really hurt...i used to get nasty shocks off my trampoline in the back yard when i would touch the frame of it after jumping for awhile....then there was that faulty vangergraf generator at work that numbed my arm for 2 hours....hehehe.

[Dave Flowerday]

Originally posted by oneangrydwarf
i wonder if first would mind if you just grounded the ramp yourself with the coathanger idea before the match started....

Since the HDPE is nonconductive, it is not possible to ground it. If you touch a coathanger between the grid and the HDPE you might eliminate some of the charge in the immediate vicinity of the coathanger contact with the HDPE, but you won't discharge the whole ramp. And regardless, after a little while the charge will spread itself out on the ramp anyway.

[petek]

Originally posted by wysiswyg
I think your wrong though because static electricity is high voltage low low current. If it was the other way around then humans would be dropping dead left and right because it only takes 1amp to stop a human heart. Some electronics are more sensitive to sudden voltage spikes then others are.

Current = Voltage/Resistance (Ohm's Law) Therefore, for a fixed resistance, current is proportional to voltage. Also, I believe the safe current level in humans is in the 10's of milliamps.

High voltage causes break down of materials and interference with electrical (or neural) systems. High current flow creates heat. Once an insulator is compromised (by high voltage breakdown) it may allow a continued flow of current, causing thermal damage.

However, in the case of ESD, there isn't a continuous source of charge. Once the initial charge is dissipated, current flow stops. This is why your PDA may lock up from ESD but can be reset and keep working.

[Adam Y.]

High voltage causes break down of materials and interference with electrical (or neural) systems. High current flow creates heat. Once an insulator is compromised (by high voltage breakdown) it may allow a continued flow of current, causing thermal damage.

Im confused isn't that what I have been saying???

[Al Skierkiewicz]

Dick,
We have tried anchor lines to no real avail. The helicopter crews actually attach a wire to the helicopter frame and then to the high line they are working on. The lineman then have a protective suit that is also "grounded to the helo frame. They found that although the lineman were not receiving any shocks they were disturbed by the hair standing up on their arms. Unlike our problem, these lines are real electricity not static and they are at such high potential they can arc across 14 ft.

[Marc P.]

Originally posted by wysiswyg
I think your wrong though because static electricity is high voltage low low current. If it was the other way around then humans would be dropping dead left and right because it only takes 1amp to stop a human heart. Some electronics are more sensitive to sudden voltage spikes then others are.

Humans are an interesting scenario- we don't die from static shocks because humans have a resistance value of between 100-300k, so not much happens with high voltage but low current. Think aluminum chasis though, what's the resistance of that? Considerably less. Similarly, what's the resistance of the electrical pathways leading to the control systems? Still considerably less. Static discharges on this level are not harmful to humans, but can be killer to any integrated circuit because of the low resistances (if resistance was any higher on IC's, they wouldn't be able to do their job).

[Al Skierkiewicz]

OK,
There is a lot of misinformation taking place here. 3-4 mA (that is milliamp) applied across the heart muscle will cause the heart to stop beating. (It actually adapts, thinking that the brain has stopped sending little pulses and has now switched to the bigger pulses. The heart is a muscle controlled by electrical impulses from the brain.) This 3-4 mA is critical and the reason that ground fault interrupters are tested and must react at 3-4 mA.
Most reports of electrical shock do not result in death simply because the circuit through the body that causes the shock does not cause current to flow through the heart.
As to static electricity, the voltage and current at the point of entry are dissipated by the body's tissues and a great deal flows on the surface. The shock causes localized pain, a muscle contraction and in rare cases a small pin point burn at the point of entry. In the ultimate static electricity strike, i.e. lightning, the bolt carries current in the millions of amps. Should you receive a direct hit, which is rare, the heat generated by the current flow cause significant tissue damage which usually results in death.
Now to the static problems with electronics, The spikes are not only causing false triggers, but the ringing associated with large voltage spikes also causes spurious data to be entered into digital circuits. In some cases the the protection devices that are engineered into the circuit cannot react quickly enough to limit the voltage and the resultant spike punches through the internal materials causing permanent damage to the device.

[Katie Reynolds]

Static Electrcity

- Katie

[Dick Linn]

Yes, Al, there is a lot of misinformation floating around. First, getting zapped by the HDPE sheet is an Electrostatic Discharge event. In our case, it is a small one. Another example of this is lightning. They differ in magnitude and in the damage they can cause, but otherwise similar. For a basic discussion on ESD, see http://www.midwestesd.org/aboutesd.html


This link (http://www.static-sol.com/61340-5-1/.../WhatisESD.htm) says "If two objects that have different voltages approach each other closely enough, charge may pass from one object to the other in a fast electrostatic discharge. While this only lasts a microsecond or less, the peak discharge current can be several Amps and the peak power can be in the kiloWatt range!" The high voltage means that even a relatively small current can generate enough power to cause damage. From what I can tell, Electro Static Discharge (ESD) waveforms are normally shown as a graph of CURRENT vs. time. As far as I can see, voltage in and of itself does nothing except initiate the event. Electrons must flow to do any harm. I suspected that it had something to do with the P-N junction and the electron depletion region - this link may shed a little light: http://cnx.rice.edu/content/m1031/latest/

In terms of protecting the 'bot, I would think a 1 MegaOhm resistor in series with a conductive string or wire (we have some conductive string from some packaging or conveyor system) might limit the inrush enough. Put one on each corner of the 'bot, and grab this first before you handle it when it comes off the ramp.

If you want a very fast device to fashion a surge suppressor, I would suggest using a zener diode or Transorb (a specially adapted zener), possibly backed up with a varistor (slower but higher current handling) if there is real energy (bust open a PC surge suppressor outlet strip and use 'em) . A resistor/capacitor arrangement might also do the trick. I've seen all of these used in the 20+ years that I've worked in the electronics industry.

As to the effect of electricity on humans, the table in this link may or may not be accurate, but gives you an indication of some of the effects of various current levels on humans: http://www.prl.res.in/~bobra/EARTH/html1/chapt3.htm

FYI, I've been zapped by 120 VAC a number of times and also by engine ignition coils in the 20,000 + volt range (not to mention electric cattle fences) . None was pleasant. I seem to recall that the body resistance was was approximately 7K Ohms, but that of course would depend on what parts touched, wet/dry hands, etc. At any rate, don't try this at home!

THIS IS A VERY SERIOUS ISSUE!!!!!

almost everytime I picked up the bot off of the HDPE at SLR, I got a nice discharge into my body. Several times over the weekend, we believe we were zapped and killed because of static.