Static Discharge Disables Robot

[Team2456]

We have been having a problem where our robot will discharge static electricity onto any nearby metal objects after a bit of driving on carpet. I've been thinking about hanging a wire mesh off of the bottom of the robot to discharge static electricity into the field.

Anybody else having this problem? And if so, anybody found a solution?

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Colin Warren
Team Captain/Electrical Lead/Programming Lead
Team 2456 - Marin Robotics

[Al Skierkiewicz]

Colin,
You can try but this method has little effect since there is no real path for the static to travel. This is usually a problem during build in the north. It goes away as air warms and the humidity of spring moves in.

[kevin.li.rit]

Originally Posted by Team2456

We have been having a problem where our robot will discharge static electricity onto any nearby metal objects after a bit of driving on carpet. I've been thinking about hanging a wire mesh off of the bottom of the robot to discharge static electricity into the field.

Anybody else having this problem? And if so, anybody found a solution?

-----------
Colin Warren
Team Captain/Electrical Lead/Programming Lead
Team 2456 - Marin Robotics

How is this actually disabling your robot?

[Nirvash]

Something similar happened when I was driving our bot down to be crated up, and when the frame got near a metal door frame there was a arc of static and the robot when into disabled mode. I was able to switch it right back to enabled and I did not notice anything wrong with it. All of our electronics are off the frame.

[Natesbug73]

We had this happen last year, it literally would give a jolting shock to anyone touching it after driving on carpet, and would arc to the lockers in the hallway if we got too close. What we discovered was that if we ran a small ground strap from the compressor to the frame, it went away.

[pfreivald]

Uh........ If your electronics are not grounded to your frame -- which you will be required to demonstrate if you wish to pass inspection -- then static discharge to/from your frame should do exactly diddly squat to your control system.

[Team#2057-Vegas]

we had ours arc to a locker.. we plan to let something hang a little. most every team will have a problem just from the friction.

"just remember to touch the bottom of your foot to the robot before touching it" is our rule to the team.. it grounds it all

[Alan Anderson]

Originally Posted by pfreivald

Uh........ If your electronics are not grounded to your frame -- which you will be required to demonstrate if you wish to pass inspection -- then static discharge to/from your frame should do exactly diddly squat to your control system.

Remember the first week of Lunacy? Before the metal bar in front of the fueling stations was insulated, robots would regularly reset when they came into contact with it and static-zapped themselves.

A brief pulse of extremely high current through the robot frame induces currents in every nearby wire. Unexpected voltages on control or power wires are quite capable of disrupting the control system. There's no way I can think of for an ESD event to just disable the robot, though. It would have to be a full reset of the cRIO, taking 20 seconds or so before it could be reenabled.

[pfreivald]

Originally Posted by Alan Anderson

Remember the first week of Lunacy? Before the metal bar in front of the fueling stations was insulated, robots would regularly reset when they came into contact with it and static-zapped themselves.

I wasn't aware of that. We had put aluminum tape on much of our robot specifically to control static.

Originally Posted by Alan Anderson

A brief pulse of extremely high current through the robot frame induces currents in every nearby wire.

Quite true, of course -- but I'm surprised that the robots are picking up enough static to generate extremely high current. One would think that the CRio, tank of a system that it is purported to be, would be sufficiently shielded from induced emf from static discharge.

...I think I learn something every time I log in here...

[billbo911]

For this exact reason, we have added a drag chain to our robots for the last three years. We simply attach a short piece of #35 chain to the bottom of the frame and let it drag on the ground (no pun intended).

We always get funny looks and comments from inspectors on our "broken drive chain". With a quick explanation, everyone is happy and satisfied.

The best part is when it actually prevents a match from starting until you explain it to the Ref. who is holding up the match.

We also have the benefit of not getting zapped our selves when we touch the robot.

[crake]

Originally Posted by pfreivald

One would think that the CRio, tank of a system that it is purported to be, would be sufficiently shielded from induced emf from static discharge.

It is... up to a point. We're not talking about "walking across the carpet and touch a doorknob ZAP" type of event here. Under the right conditions, these robots can build up a large charge at a HUGE voltage (20kV? 30kV? higher?), and if the electronics is not properly grounded then not only are you looking at a possible reset, you could also destroy the radio and/or camera.

Edited: to clarify charge vs. voltage.

[crake]

Which reminds me - everyone is using properly grounded work stations with wrist and shoe straps when handling the bare-board electronics. Right? No? Then at least grounding oneself by touching a grounded frame? Please?

Think of working on the inside of a computer - you wouldn't want to dive in without discharging yourself. Your robot electronics (especially bare-board components) aren't much different.

[pfreivald]

Well, a balloon rubbed on your head can be 5 to 10 kV, too, but the amount of charge stored on the balloon is sufficiently small to render it quite harmless... That comment wasn't a criticism so much as a statement of "huh."

I'm wondering what we're doing differently that we never get zaps from our robot, in spite of building during the driest time of the year and without having special tricks to keep from getting shocked... ...because I'd really rather it not happen to our robots during a game!

[Alan Anderson]

Originally Posted by pfreivald

I'm wondering what we're doing differently that we never get zaps from our robot, in spite of building during the driest time of the year and without having special tricks to keep from getting shocked... ...because I'd really rather it not happen to our robots during a game!

I'm pretty sure the biggest contributor to the difference is wheel material. We never get zapped from the practice robot wearing metal wheels, but we always get zapped, sometimes repeatedly, from the Lunacy 'bot and its hard plastic wheels.

[pfreivald]

We've run mecanum the last couple of years, so that might have something to do with it as well -- metal wheels and rollers that spin across the floor might help.