FTC- preventing ESD
 

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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Re: FTC- preventing ESD
 

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.

Re: FTC- preventing ESD
 

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.

Re: FTC- preventing ESD
 

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?

Re: FTC- preventing ESD
 

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.

Re: FTC- preventing ESD
 

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.

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?

Re: FTC- preventing ESD
 

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.

Re: FTC- preventing ESD
 

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.

Re: FTC- preventing ESD
 

Agreed! Add this to the list above.

Re: FTC- preventing ESD
 

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)?

Re: FTC- preventing ESD
 

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.

Re: FTC- preventing ESD
 

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.

Re: FTC- preventing ESD
 

2003. There was a lot of moving plastic in that game and the wheels in the KOP had a lot to contribute.

Re: FTC- preventing ESD
 

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.

Re: FTC- preventing ESD
 

I have seen very little in the way of Matrix hardware here in Illinois. It would seem to be more regional than anything.

Re: FTC- preventing ESD
 

Yeah, the NXT controller locking up during competition is an odd anomaly. I use to blame static as the cause of the NXT locking up, primarily because once we sprayed anti-static spray on the floor mats the teams with the lockup problems would significantly reduce. We also thought the NXT itself was to blame, and teams this year who were having lockup problems literally replaced the NXT for NXTs that never had the lockup problem, and lo and behold the lockup would show up on the new controller the very next match.

My FTC team this year did everything that is recommended by all the "best practices" documents - mounting electronics on lexan, insulating everything, yadda yadda, and we still ran into NXT lockups this year. Our lead programmer then tried to determine if there was a place in the code where the NXT locked up the most, or if it was random. Sure enough, he found a spot where if it was GOING to lock up it DID (meaning the controller only locked up when it hit a particular piece of code - though locking up was not guaranteed, the controller only seemed to lock up at that point in the code). We use LabVIEW, so there's no "crazy" pointer manipulations or NULL references (in our code) or what have you, but the lockup was actually in setting the motor speed. The crazy part was if we just deleted that command in the code, the lockup stopped happening, and even when we added it back the lockup did not happen. However, pulling the original code out of source control and running allowed us to reproduce. LabVIEW compiler error was all we could come up with, though the VIs in the reproducing case and the non-reproducing case were perfect matches.

I then wanted to blame LabVIEW, but it wasn't limited to LabVIEW. Teams using LabVIEW and RobotC had the problem just as much (almost equally so). I almost now want to blame firmware, but I have no basis to make that claim.

I'm really hoping the EV3 solves this problem, if in fact FTC is moving to the EV3 (which blog posts seem to claim, but the same blog posts claim there will still be support for the NXT next year).

-Danny

Re: FTC- preventing ESD
 

It's coming. Just not sure on the exact date yet.

Danny:
Did your programmer document their findings in any sort of way. If they did, I'd like to take a look at them.

We had a half dozen teams or more using the Matrix out of almost 150. Aside from initial issues in getting it up and running, they didn't have any of the normal issues, Al. The only thing is with the radio on it's own power supply, FCS reads it as bad but in fact on it's own source that one battery last all day.

Re: FTC- preventing ESD
 

Unfortunately we were all mystified by what we found, and we were more in a "how do we keep this from happening to us" mode rather than a "let's document this issue" mode. Now that FTC has ended for us, I will ask my programmer to document what we found, if he is able to reproduce again.

-Danny

Re: FTC- preventing ESD
 

Thanks. I wanna try and replicate it on a show robot. Just inbox me with the information.

Re: FTC- preventing ESD
 

IMHO this is ESD on the I2C lines. They're the single weakest point in the whole system and a really bad choice (dictated by the NXT) for motor control since these lines are high impedance and have a fairly direct path to the micro. Okay so there's some protection inside the NXT but it's going to be whatever a standard called for and likely 15kV plus when it happens data corruption is likely. If there's no error checking on the I2C bus transactions (and there isn't to my knowledge) who knows what firmware "issues" are lurking about unexplored and untested.
As a side note the VEX system introduced a new motor encoder in 2012(?) which connected via I2C. This was the first I2C sensor for use with the cortex based controller and what a disaster! It took quite a few firmware revisions before these became *almost* as reliable as the old quadrature encoders that just connected to I/O ports.

I don't see this going away with EV3 because it too is I2C.

Re: FTC- preventing ESD
 

Thank you everyone for your wonderful insight. We have some specific questions to ask:

1. Why would shortening the USB cable be of benefit?
2. If rubber doesn't conduct, why do the 'normal' friction wheels generate so much static?
3. Is there a way to neutralize static as it is generated?

Re: FTC- preventing ESD
 

I don't know who mentioned to shorten the USB cable, but shortening the USB cable won't necessarily do anything about the static itself. Unless the cable is rubbing against something that is causing charge static to build up on the cable, I think this is a red herring. However, keeping the USB cable as short as possible is always a good suggestion for FTC robots anyway. I cringe when I see robots with less than 1 foot of space between the NXT and the Samantha module (even considering bends and such) and using a 6' USB cable to traverse that length.

If rubber balloons don't conduct, why do "normal" balloons generate so much static when rubbed against hair? The answer to both questions is the same. I'm sure you can use Google to answer them, but be sure to include the term "Triboelectric Series" somewhere.

The primary way to get rid of static that has built up is to provide a path to a highly positive source. Like the earth. Aside from that, there's research being done to develop materials that can do that. Anything we can do on our robots? These guys seem to have figured something out. Here's also a series of videos they have in "building a better robot" where they talk about "grounding" plastic and shields to the robot chassis. The same team also claims to wipe down their robot with their homemade anti-static mix before each match to minimize static buildup. FIRST use to recommend the use of polycarbonate between the motor controller and the chassis to act as a dielectric, but they've since taken that document down (in the last 2 months). In practice, static electricity is a big "guessing game" of how to deal with it, you pretty much just have to create products that can "deal" with it (or else, zap).

-Danny

Re: FTC- preventing ESD
 

Please note that the video has poly sheet completely surrounding the wheels. As anyone who has worked with Van de Graff generators knows, the moving of materials in close proximity to each other produces significant static buildup. In designs where this is unavoidable, a wiper/brush rubbing on the moving surface and connected to the stationary surface would drain off accumulated charge. Remember that static does not need a conductive surface in which to accumulate as Danny pointed out in the balloon example.
I inspected an FTC robot this year that used a little USB jumper with Radio Shack ferrite cores at each end to prevent any interference. They claimed it worked, I was a little skeptical as the two cores were only an inch or so from each other. Ferrite will not prevent ESD but it does serve to reduce noise currents flowing on the surface of the wire around which it is placed.
The copper tape used in the video, if the 3M product I am familiar with, has conductive beads embedded in the adhesive layer. It is very good at conducting low frequency energy and shielding. It is awful for use at HF and above, making for a very poor RF radiator. (My first hand experience making an antenna using this product.)

Re: FTC- preventing ESD
 

A great set of videos which span a great many topics besides the static discharge events. Great find Danny and as always with these types of tutorials, user benefits may vary and one needs to do the work to learn the why of what is being suggested as a best practice. Don't fall into the trap of taking another team's/expert word as truth without reading and studying the issue yourself. They may in fact be promoting a sound practice but you need to understand the why and because of it if you want to earn points in the judge room. You can credit the source and back it up with your own solid understanding of the need/issue.

Caution, they support tinning wires which goes against the advice of Al.

I'm still promoting the use of these videos by FTC teams in my area as a tool for improving robot design.