Mitigating static buildup & discharge

Technical Electrical
#1

Hi All!

We’ve been noticing static electricity discharges from our robot whenever we’ve been driving for long enough, and a metal part touches a metal field element.

Based on experiments the static seems to be building up while driving around. Sitting still and cycling the intake/shooter doesn’t accumulate charge.

We’re driving on 6" colson wheels, on carpet that should be remarkably similar to field carpet. 4 NEO drivetrain through WCP flipped gearboxes, versablock mounting system…

The real issue, other than the surprise electroshock therapy: sometimes the discharge appears strong enough that our radio briefly stops communicating. Not a full reset or reboot on the radio, just disconnects from the roboRIO and our PI vision processors for about 15 seconds, then reconnects. We’ve done this at super low speeds, or by just barely grazing a metal robot part against another piece of metal - based on this I’m entirely convinced it is indeed the audible and visible static discharge, not some mechanical jostling of loose wires.

Frame to battery impedance is effectively infinite (beyond what any meter we have can read).

We’re considering dragging a fabric grounding strap on the ground, and putting ferrite beads on all wires leading to the radio.

Anyone dealt with something similar before? I saw lots of 2009 posts about it, but not a ton of “here’s the silver bullet fix!” Any other root causes or mitigations folks can think up?

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#2

This doesn’t surprise me, especially during winter when the humidity is low. We saw the same thing often while using Vex mecanums (plastic frame) instead of the Andymark mecanums (metal frame reaching very close to the carpet). I suspect we’ll see it again this year with our 6" Colson drive base. The grounding strap is a good idea and seemed to work for us at the time. I’ll need to remember to add one to this year’s machine.

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#3

Sweet, this is a great vote of confidence. If you don’t mind, how do you usually construct yours? Our running idea was to use conductive fabric tape wrapped around a piece of something heavy, then dragged under the center of the robot. Hopefully the “fabric” portion prevents any inspection woes about “no metal engaging the carpet”.

#4

In several previous seasons, EagleForce as it hatched a small section of number 25 chain, no more than 5 links, to the frame of the robot. It is love to hang down and just touched the carpet. This seems to remedy the static discharge issue. It also generates a lot of funny looks and questions from inspectors and referees.

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#5

Try wiping dryer sheets borrowed from your laundry room on the outer surfaces of your wheels. It leaves a static disapative coating that is very, very mildly conductive, allowing the static charge to bleed away. The product used in electronic manufacturing facilities is Staticide. I have seen it sold on Amazon but it tends to be in larger quantities so hobbyists use the dryer sheets.

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#6

I used leftover material from my foil hat. :wink:

They were a short chunk of stranded wire that barely reached the carpet. The last inch was stripped and fanned out a bit. Not fancy, but kept the charge from building up.

I need to try that dryer sheet idea now.

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#7

In 2009, many teams sprouted grounding straps of various lengths. It helped some–considering that the robot wheels were Van de Graaff generators!

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#8

It may be necessary to reapply the dryer sheets periodically.

The dragging chain is a good idea as long as the RI and LRI are ok with them

#9

The way dryer sheets work is by applying a coating to help the fibers in the fabric retain a small amount of moisture. Enough to prevent a static charge from building up when everything is being rubbed against each other in the dryer. It’s the same thing with other anti-static products, the coating isn’t actually conductive in itself. So for metals and plastics it won’t do much.

Really it’s all about humidity. In places where sensitive electronics are handled the humidity is controlled to reduce static build up. The most effective way to reduce static buildup on your bot is to mop the floors and spray your carpet with a light mist of water.

In terms of mechanisms I’ve seen some affect from applying aluminium tape to plastic surfaces just to help spread the charges over a larger area