Static electricity blowing out V5 3-wire Expanders

Hi all,

My team has had 3 of the 3-wire expanders gone bad, likely blown out by static electricity, all during the past 2 months of cold weather in Texas. The v5 ports on these bad expanders flash red when connected to the brain.
2 of them were on a lift that is electrically isolated from the chassis. After those 2, we moved the 3rd to the chassis, connected to a solenoid and a potentiometer from the lift, and we just had it blown out again this last weekend. Funny that we haven’t had any brain port blown out yet (knock on wood).

Has anyone had static problems with the 3-wire expanders? Any potential solution to this?
The tournaments we went to didn’t have any anti-static tile or sprayed tile. So, it is kinda outside of our control.

Static is caused by “floating metal”. Make sure that all metal on your robot is grounded in the future. The V5 brain has notoriously bad ESD protection.
You can’t really fix this without violating competition rules. If you can find a way to replace a 3 wire expander, you can use it for practice.

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I haven’t had specific experience with the 3 wire expander, but my general approach towards static on non-sprayed fields is:

  1. Coat your wheels in anti-static spray, this is allowed under R8C
  2. Have a short metal string hanging off your robot so it touches the field, this is allowed under R8E

My theory to static buildup is that the VEX wheels and foam tiles creates a Van de Graff generator with the metal chassis acting as the ‘sphere’.

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I have a question. Our robot used to build up a ton of static because there was a polycarbonate ramp that drug on the ground this blew out one of our ports and at the end of each match whoever picked up the robot would get shocked. We fixed this by lifting the ramp of of the ground and ever since we haven’t had any issues. But we don’t have aby sort of grounding wire should we consider adding ones as s Preventative measure?

On your 2nd suggestion, this post seems to indicate it is counter-productive with non-sprayed tiles:

We do have small metal wires to bridge the isolated parts after we blew the 1st 2 expanders. So, the robot is one big Van de Graff.

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That’s weird, I’ve used the grounding wire on non-sprayed fields before and it helped us not get shocked by the robot.

Here's an idea for an experiment to test this out:

(Full disclaimer: I take no responsibility for damages to your robot)

The experiment will test the effectiveness of the grounding wire by comparing the relative distance needed to discharge.

Control group: robot without grounding wire
Test group: robot with grounding wire

Drive the robot around the field for a set amount of time
Start recording with a camera in slow motion mode, then see how close you can get a wire attached onto the field perimeter to the robot without a spark forming. You can roughly gauge the distance by replaying the video. Run this a few times to get some data samples to rule out outliers.

Analysis:
Distance for test group > Distance for control group:
-Grounding wire helps

Distance for test group = Distance for control group:
-Grounding wire doesn’t do anything

Distance for test group < Distance for control group:
-Grounding wire is counterproductive

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You really need to search and read my thread on static. I bought a static meter and performed several experiments with it.

The short version of all that is:

  1. anti static spray, not tons of it, just a light misting
  2. metal shaft lock collars for all motors… and have the lock collar touch the chassis… help prevent the electricity from traveling from clamp/etc through the shaft, into the motor, through the wire, into the brain.
  3. anti static spray
  4. try not to drag anything plastic across the field
  5. anti static spray
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@turbodog First of all, appreciate your sharing the detailed experiments. They were super insightful and helpful.
Secondly, I did read your thread on static, which I had linked in a reply above to Amadeus about grounding being counter-productive on non-sprayed tiles. Is it correct that this is counter-productive?

As I mentioned in original post, we cannot control the fact that our local tournaments do not have anti-static tiles or sprayed tiles. I suppose we can try applying anti-static spray on the wheels.

I’d say the verdict is not 100% for dragging a ground wire or not.

My gut feeling, and most of my data, says it works. But we did get some weird readings on a NEVER-sprayed field.

Short version… static spray on field & wheels, metal shaft lockers between motor and the AL/FE plate it’s mounted to, be careful dragging plastic.

And do NOT grab the bot by motor, wires, or brain. Grab the chassis first.

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I am scared, very scared

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