FTC- preventing ESD

[Lat Mac]

We noticed that at competitions our robot is effected by ESD. What can we do to prevent this? What are some possible causes?

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[Hibrawler]

I was on an FTC team in 2011 and though we didn't have any problems I know why this is caused and how to fix it. The friction between the floor tiles and the robot wheels cause static electricity. The easiest way to fix it is just to do a wire that is crimped into a crimp terminal which is bolted to your robot frame. As long as the wire is dragging on the flood it will keep your robot relatively grounded.

[pyroslev]

FIRST investigated the drag chain/wire concept a few years back. Apparently it creates more problems than it will solve.

http://ftcforum.usfirst.org/showthre...ull=1#post7994

Also compare the FTC robots to FRC robots. The FRC robots 'mass' (size, bumpers, larger frames, etc) allow this work where as FTC it is a great concept but the 'mass' isn't there.

What happens is all the robots drive around. The wheels are van de graff generators. With omni wheels, each roller is an additional generator. Treads also suffer being 2 large VDG generators. The charge is translated into the frame and becomes a leyden jar.

So each robot has varying charges. When robot contacts robot or field elements, discharge occurs where the charge tries to equalize. This results in a robot being locked up sometimes. Higher fidelity (intense gameplay) matches can see this happen more.

Simple solutions involve isolating your electronics from the frame. You can take your pick but simple clear coat or powdercoating works. Even electrical tape on the back of your motor controllers can take a bite out of things.

Other factors affect ESD. If the humidity is under 30%, the risk goes up. In winter, cause air is heated up mechanically water is cooked out of the air so it gets drier. Winter and snowy places also experience higher static risk. If you're fields are on tarps, that adds another factor raising the risk.

I could go on further. Bottom line is you're fighting an uphill battle in an avalanche. Best of luck and don't use the drag wire.

[CENTURION]

I'm not very knowledgeable about electronics in general, but I've always been confused as to why this is an issue.

FIRST, and others, recommend isolating your electronics with plastic sheets, but I don't see why this would help. The motor controllers, samantha, and NXT all have plastic enclosures already. So why aren't they isolated when used on their own?

Basically; how does the static actually get from the frame to the electronics? And furthermore, how does it get from the wheels (Rubber and plastic) to the frame?

Is there some big electrical concept I'm missing here?

[pyroslev]

Originally Posted by CENTURION

The motor controllers...have plastic enclosures already. So why aren't they isolated when used on their own?

How does the static actually get from the frame to the electronics?
And furthermore, how does it get from the wheels (Rubber and plastic) to the frame?

Your wheels/treads are sliding along on the tiles, the same way your socks slide along on carpet. This builds up a charge. Said charge is transferred into the frame through the metal drive shafts. The frame acts as a Leyden Jar/Baghdad Battery. The charge is not relatively high to the human touch but to electronics it is.

When your robot contacts an object with a differing charge, which can be the robot or a field element, the charge equalizes. Think about lightning. It takes the path of least resistance. Insert your electronics here.

If your electronics are mounted to the bare frame, your electronics provide a pathway for the static charge that has built up. The common path you'll see starts from frame to motor controller. The back of the motor controller has 4 metal screwheads. These when in contact with the frame are a direct line for that charge. (The Matrix Controller's screwheads are recessed almost a half inch)

Here the charge can cause the motor controller to lock up. This is not as common but it happens. If this doesn't happen, then the charge is sent to either the Samantha or the NXT. If it is the Samantha, it could lock up the Sam but it has ESD protection. This would send it down the USB cord. If the Samantha locks up, Only the power light will be on.

If the charge goes into the NXT, from the controllers or the Samantha, this can cause a lockup. The NXT has some ESD protection but it can't handle the charge your robot generates. If it fully locks up, the best the FTA can do is turn it off.

I learned all of this not from any one event or document. It's the culmination of a long learning process.

[CENTURION]

Originally Posted by pyroslev

Your wheels/treads are sliding along on the tiles, the same way your socks slide along on carpet. This builds up a charge. Said charge is transferred into the frame through the metal drive shafts. The frame acts as a Leyden Jar/Baghdad Battery. The charge is not relatively high to the human touch but to electronics it is.

Does static conduct through plastic or rubber? Because I'm pretty (Again, I fully admit that I know very little about electricity) sure those are both insulators, and almost all robot wheels are made out of those two materials.

That said, the only time we got shocked this year was when we had frame-to-frame contact with another robot, so the material in our wheels might not have even mattered. I'm just trying to understand the phenomenon here.

Originally Posted by pyroslev

The back of the motor controller has 4 metal screwheads. These when in contact with the frame are a direct line for that charge. (The Matrix Controller's screwheads are recessed almost a half inch)

DUH! I didn't realize those screwheads could be an electrical path into the controller. That solves my "How does the charge get into the electronics" problem.

Is there any chance that the static charge could also be carried through the motor leads into the controller?

[Al Skierkiewicz]

Guys,
A drag chain does nothing but make the team feel good that they have solved a problem. This goes back to an automotive accessory that was sold in the fifties that attached to the bumper to reduce static in the AM radio. On most FTC robots, ESD events would be visible and harmful if they were the problem. The NXT and EVO are tested and designed to prevent issues from ESD. Most of the other components are also designed to minimize issues from static discharge. The majority of issues on FTC robots are due to just a few minor electrical problems that could be easily fixed with a better electrical design.
1. Loose USB cables to the Samantha cause noise and therefore data corruption. Simple fix is to secure the cables near both the controller and the Samantha so that they don't move during operation.
2. Teams have decided to tin the wires they use in FTC robots. This is one of the worse things you can do. The screw terminals are designed for stranded, bare copper wire.
3. The size of the wire used to feed the motor controller should be #16 or #18. Using a smaller gauge wire causes significant losses. This is more of a problem for teams using multiple motors on a single controller.
4. Daisy chaining the power on motor controllers and then feeding the Samantha at the end of the chain drops the supply voltage to the Samantha. Use power distribution by splicing power wires or by using a Power Lock distribution device if you use these connectors. Again use #16 or #18 wire.
5. Keep wiring short. While the Samantha is a low current device, the motor and controllers are not. The currents they require can cause significant voltage losses when used with long or small gauge wire.

[pyroslev]

Originally Posted by CENTURION

Is there any chance that the static charge could also be carried through the motor leads into the controller?

It wouldn't surprise me. I just know most the time when I touch a robot that's locked up, I get shocked or I did anyway. In one situation, I got shocked on three sides of my arm reaching into a robot that was all heavy metal.

And while all the components in the standard FTC robot have some sort of ESD protection, sometimes the sheer amount generated overwhelms the systems. Even the Samantha's ESD protection isn't perfect.

Al, you're right. I keep notes on all of the issues I see at events. 95% of them are electrical in nature. The remaining 5% are split between coding and lockups. I would add the infamous Tamiya Connector should be swapped for Anderson PowerPoles the first opportunity.

[Al Skierkiewicz]

Originally Posted by pyroslev

I would add the infamous Tamiya Connector should be swapped for Anderson PowerPoles the first opportunity.

Agreed! Add this to the list above.

[CENTURION]

Thanks for all the info Al!

I'm still wondering about the NXT lockup then. Could that be caused by jostling and bumping on the field (Connectors wiggling loose)?

[Al Skierkiewicz]

Evan,
That seems to be the case in most lockups according to the CSAs. It also depends on the batteries you use for the NXT. If you are using the standard single cell battery pack, the terminals sometimes need to be realigned. In the heat of battle, they become deformed and do not hold a tight connection in motion. It is similar for the rechargeable packs but they don't seem to be as critical. Remember that there is always other issues in the way you write your code as well. I am not an expert in this part so take this with a grain of salt. If your program is waiting for input from a sensor that has become disconnected or is intermittent, then you may experience unpredictable results. In that case, the software is running but it is merely waiting for an expected input that never comes.

[fox46]

I remember our robot in Stack Attack (2002? I think) used to discharge in a visible arc as it crested the ramp and part of our frame came close and contacted the steel mesh on the ramp. We never had any issues with electronics back then due to ESD. Although it was a different control system, I would expect the CRIO is more robust than the ones used back then.

[pyroslev]

Originally Posted by Al Skierkiewicz

It also depends on the batteries you use for the NXT.
Remember that there is always other issues in the way you write your code as well.

I'd not considered the battery issues before but that would explain one or two issues I've had this season with some teams.

RobotC compiler is FAR from perfect. A veteran team was having their brick lockup every time they were practicing their autonomous. Turned out at least 1 or 2 serious errors slipped past the compiler.

Based on the number times I've been shocked diagnosing a locked up robot, ESD plays a factor. Funnier thing is teams using the Matrix kit have not seen a lockup. I'm not sure if it's due to that or just not enough teams using it, wear and tear or another factor. It's something I'm going to be keeping an eye on.