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OT: Any EE, ME, Chem.E, Comp Sci guys out there

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David_RU

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Nov 29, 2006
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So this post will probably take the OT nature of out of season football posts to a new level. I'm involved with my daughters FIRST FTC robotics team. This is very similar to what many high school robotics teams compete in - its the same organization but the robots we build are smaller and open to younger kids (12 - 18)

See https://www.firstinspires.org/robotics/ftc for a bit more info on the program if you're interested.

The team is having an issue with their robot that is out of my area of expertise. Our drivebase uses mecanum wheels (the rotating wheels that contact the floor are nylon core with a urethane rubber coating). The floor of the playing field is composed of those interlocked foam tiles. One of the natural effects of mecanum wheels is that they tend to build up charges due to how they operate (probably triboelectric effect). You end up with a charged robot where you'll have two outcomes.

The first is a major issue for us. The robot builds a charge, bumps into something during gameplay of the opposite charge and discharges. This causes the phone\computer to freeze up ending the match for our robot. A hard reset of the robot fixes the issue after the match. This does not happen every match but it happens often enough and at "random" intervals. The other outcome is funnier, they pick the robot up to take it off the field and get a little static zap and we all go haha. I guess there is a third outcome as well...no shock to the kids and the robot works flawlessly.

Anyway, we've been working with some of our sponsors on solutions but have not come up with anything concrete yet to fix the problem. We've added some ferrite chokes, tried to insulate the phone as best as possible, connected the drivebase to other components with wires in an attempt to spread the charge over the entire robot. Wiped the robot down with static spray or dryer sheets...nothing has really worked so far.

An unfortunate rule of competition is that the robot can not be grounded to the field.

My question for anybody that read this far is: Help! We're working with some engineers from one of our sponsors but they're mostly at a loss as they dig into the problem with us. If anybody has suggestions or wants more information, let me know and we can get in touch off of the board.

The kids built a really nice robot that just qualified for the regional tournament out in Scranton in a few weeks and we're hoping we can come up with a solution before then.

thanks in advance.
 
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RU4Real

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If the wheels on the playing surface are the source of the static potential, can you isolate the wheels, electrically, from the rest of the robot? I'm assuming all the gearing, shafts, etc., are somewhat conductive. What if you introduced a non-conductive gear assembly or axles into the mix?
 
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David_RU

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RU4Real said:
If the wheels on the playing surface are the source of the static potential, can you isolate the wheels, electrically, from the rest of the robot? I'm assuming all the gearing, shafts, etc., are somewhat conductive. What if you introduced a non-conductive gear assembly or axles into the mix?
Click to expand...

Thank you, I'll bring this up to the team. Some of the EEs that we are working with suggested something opposite of that - get everything connected to spread the charge and then isolate the electronics with insulators and ferrite chokes.
 
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RU4Real

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Jul 25, 2001
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David_RU said:
Thank you, I'll bring this up to the team. Some of the EEs that we are working with suggested something opposite of that - get everything connected to spread the charge and then isolate the electronics with insulators and ferrite chokes.
Click to expand...

That would protect the electronics from any potential developed in the chassis, but wouldn't necessarily protect anyone who picked the thing up from getting zapped.

Here's a crazy idea - get your EE gurus to design a charge storage circuit. Basically, short electrical ground into the anode of a big capacitor. Then wire the cathode into some kind of probe out the front of the robot. It will discharge into its opponent on contact.

That might be against the rules... lol
 
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RW90

RW90

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Feb 2, 2002
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David, being the software development mentor on my son's high school team, I can tell you firsthand that FIRST inspection rules require the robot's ground be isolated from chassis by 3 Kohms or more. I've often observed an ESD discharge touching our robot, so I don't think that's out of the ordinary, especially with all the aluminum tubing in the frame and chassis.

Stoopid question, but are you certain it was an ESD discharge and not a software bug that froze the robot? Do the test logs actually show any correlation in battery voltage about the time the robot ceases? Working more on the software development side I've seen my share of bugs in the code that could potentially stop the robot also, so I wouldn't rule that out either.

If you haven't checked already, a good source of information are the Chief Delphi message boards. You can often find many answers and advice if you have the time search through all the threads. Best of luck this season (being as we're extended family, lol), maybe we'll run into each other as we're competing at Hatboro-Horsham this weekend and then Montgomery later this month.
 
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RU4Real

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RUScrew85 said:
Meh. 220, 221, whatever it takes.
Click to expand...

 
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Knight Shift

Knight Shift

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May 19, 2011
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David_RU said:
So this post will probably take the OT nature of out of season football posts to a new level. I'm involved with my daughters FIRST FTC robotics team. This is very similar to what many high school robotics teams compete in - its the same organization but the robots we build are smaller and open to younger kids (12 - 18)

See https://www.firstinspires.org/robotics/ftc for a bit more info on the program if you're interested.

The team is having an issue with their robot that is out of my area of expertise. Our drivebase uses mecanum wheels (the rotating wheels that contact the floor are nylon core with a urethane rubber coating). The floor of the playing field is composed of those interlocked foam tiles. One of the natural effects of mecanum wheels is that they tend to build up charges due to how they operate (probably triboelectric effect). You end up with a charged robot where you'll have two outcomes.

The first is a major issue for us. The robot builds a charge, bumps into something during gameplay of the opposite charge and discharges. This causes the phone\computer to freeze up ending the match for our robot. A hard reset of the robot fixes the issue after the match. This does not happen every match but it happens often enough and at "random" intervals. The other outcome is funnier, they pick the robot up to take it off the field and get a little static zap and we all go haha. I guess there is a third outcome as well...no shock to the kids and the robot works flawlessly.

Anyway, we've been working with some of our sponsors on solutions but have not come up with anything concrete yet to fix the problem. We've added some ferrite chokes, tried to insulate the phone as best as possible, connected the drivebase to other components with wires in an attempt to spread the charge over the entire robot. Wiped the robot down with static spray or dryer sheets...nothing has really worked so far.

An unfortunate rule of competition is that the robot can not be grounded to the field.

My question for anybody that read this far is: Help! We're working with some engineers from one of our sponsors but they're mostly at a loss as they dig into the problem with us. If anybody has suggestions or wants more information, let me know and we can get in touch off of the board.

The kids built a really nice robot that just qualified for the regional tournament out in Scranton in a few weeks and we're hoping we can come up with a solution before then.

thanks in advance.
Click to expand...
Interesting problem. Not sure if this thread proposes an actual fix:
https://www.vexforum.com/index.php/8920-possible-problem-with-robotc-3-54/p3#p83671

There is a post about static electricity in the winter months. When I was a process engineer in a plant that made a fiber product, we would have wicked problems with the fiber getting stuck to metal equipment. We designed a solution that dispersed a high humidity in the problem area and that solved the problem. My materials/chemical engineering suggestion is to put a vaporizer on board the robot and direct the vapor at the wheels. Yeah, that won't work.
 
D

David_RU

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@RW90 im pretty sure you won’t see us - we are FTC not FRC. Our state level events are done for the year now. I’m pretty sure your team is FRC. Our rules explicitly state that we can’t ground the robot to the field and there aren’t any measurements taken of grounds on the robot during inspection.

We’ve considered software issues. That’s one of the first things we saw in our research. Early in the build process we had some long timeout issues because our programmer made some errors but I’m pretty sure his code is solid.

We’ve done some testing with a static meter. Pretty neat device one of our EE friends loaned us. Point it at the surface and it reads the charge.

My hope was that I’d post this and somebody on the board would say that they ran into an issue like this at work and here is the $12 fix.

The Vexboard threads were something we ran across. Neat info there but no real solutions unfortunately. Maybe a materials engineer can point me to a non conductive coating we can put on the wheels to minimize the effect.

@Knight Shift Im a chemist and our entire facility is class 1 div 1, static is not my friend. Humidity was the first thing that came to my mind also lol.

Ah well, at least some people had nice diversions and humor in here. Thanks everyone!
 
e5fdny

e5fdny

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mildone said:
See, I actually think it's the "bad" posts that make us the best board out there. :D
Click to expand...
The thing with that is our “bad” (which are really good, smart and sharp) ones like a Dennis Miller monologue go right over the heads of some of our visitors.

And some of our regulars too. :stuck_out_tongue_winking_eye:

So I guess we’re both right.
 
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CERU00

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I deal with ESD issues daily... problem with isolation is that there is a field component. Without having a proper ground you really need to minimize the triboelectric effect. Remember the triboelectric effect is generated when two different materials make contact and separate. Maybe look at the triboelectric series and identify materials that are close to the floor foam. Is it possible to coat the wheel with some form of it. That should help reduce the magnitude if the charge buildup. Making the wheels out of dissipative version of plastics like uhmwpe or delrin would also help if you could dissipate the charge enough. If you had enough power you could mount an ionizing blower across the contact points. It wouldnt stop the charge buildup but it might be dissiapted enough to prevent the large discharges. Finally build a Faraday cage and put the phone in it...
 
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David_RU

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Nov 29, 2006
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CERU00 said:
I deal with ESD issues daily... problem with isolation is that there is a field component. Without having a proper ground you really need to minimize the triboelectric effect. Remember the triboelectric effect is generated when two different materials make contact and separate. Maybe look at the triboelectric series and identify materials that are close to the floor foam. Is it possible to coat the wheel with some form of it. That should help reduce the magnitude if the charge buildup. Making the wheels out of dissipative version of plastics like uhmwpe or delrin would also help if you could dissipate the charge enough. If you had enough power you could mount an ionizing blower across the contact points. It wouldnt stop the charge buildup but it might be dissiapted enough to prevent the large discharges. Finally build a Faraday cage and put the phone in it...
Click to expand...

Do you mind if I email you off the board to discuss some things?
 
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David_RU

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I know everyone is dying for an update. We are 99% sure that we solved the issue. A neighbor of one of the team members parents is a pretty successful EE. He asked if he could see the robot. He looked, traced some wires, pulled out a high end multimeter and started taking down some numbers. It wasn't a perfect test but the best path for a static charge in our robot went directly through our phone because of how everything was bonded and tied together.

He had us isolate the control system (the phone and one other piece of hardware) and tie them to a floating ground and ceramic capacitor. In essence, the capacitor takes the hit and slowly bleeds out the charge to the ground, saving the phone.

Thanks again to everyone that offered tips and suggestions.
 
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e5fdny

e5fdny

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David_RU said:
The Libyans are pretty upset with us over the whole plutonium mix up. I meet with them later at Twin Pines, I anticipate being able to smooth things over.
Click to expand...
As long as you got your jiggawatts who cares, right? :stuck_out_tongue_winking_eye:
 
iReC89

iReC89

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Good luck at regionals! Our rookie FTC team had a rough but productive year. Their mecanum issue was that the x-drive configuration tore up the foam. Bot 2.0 did much better and they are still working getting ready for next year. They really only started around mid November so it is pretty amazing to me that they got on the field at all.

Will be at Hatboro too RW90 - good luck - looking forward to it. I'm a little concerned about the wind and all of those small trailers heading to PA Friday.
 
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GoodOl'Rutgers

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Here's another search result...

https://ftcforum.usfirst.org/forum/ftc-technology/5131-electro-static-discharge-mitigation

Based on our observations over the past year, the risk that a large ESD event can disrupt a robot is relatively low. However ESD is a regular, naturally occurring phenomena and there are steps that teams can take to help reduce this risk even further:

Static Dissipation
  • When Teams arrive at the Field, a member of the drive team should touch the metal frame of their robot to the metal frame of the Field perimeter prior to placing the Robot on the Field.
  • Doing this should help dissipate any charge buildup that occurs off of the Field.
Robot Construction/Wiring
  • Mounting the electronic components of the robot onto non-conductive substrates (such asa sheet of dry plywood, a piece of PVC Type A, or even a polycarbonate sheet) and using non-conductive fasteners (such as zip ties or nylon bolts and nuts) can help reduce the likelihood that an ESD event will disrupt the robot operation.
  • Using shorter runs of cables and wires, and keeping the cables and wires off of the frame of the robot (for example, by routing them through PVC Type A pipes or some other non-conductive conduit) can help.
  • Covering or cladding the exterior parts of a robot with a non-conductive material reduces the risk that metal parts of the robot will touch a metallic object on the field and cause an ESD event. Wooden bumpers, cloth/tape and other non-conductive coatings can help.
 
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David_RU

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In case anybody that posted some help\jokes for the team was curious, we competed in the East Super Regional out in Scranton from Friday - Sunday. Our team won 7 matches out of 9 and advanced to the World event in Detroit in late April.

In the state tournament we had 4 static events in our 5 matches. At the regional we knocked that down to only 1 with the changes that we made. We're going to disassemble the robot and coat the aluminium frame with a non-conductive anti-static coating.

Thanks again everyone for trying to help us out.
 
Knight Shift

Knight Shift

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David_RU said:
In case anybody that posted some help\jokes for the team was curious, we competed in the East Super Regional out in Scranton from Friday - Sunday. Our team won 7 matches out of 9 and advanced to the World event in Detroit in late April.

In the state tournament we had 4 static events in our 5 matches. At the regional we knocked that down to only 1 with the changes that we made. We're going to disassemble the robot and coat the aluminium frame with a non-conductive anti-static coating.

Thanks again everyone for trying to help us out.
Click to expand...
What is the coating?
 
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David_RU

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Knight Shift said:
What is the coating?
Click to expand...

Techspray 1756-8S is a colorless licron crystal ESD-Safe coating that comes in an 8 oz aerosol. The versatile spray provides exceptional adhesion to metals, plastics, and other surfaces,

Techspray 1756-8S Features:
  • Series: 1756
  • Product Type: Licron Crystal ESD Safe Coating
  • Material Compatibility: Metal, Plastic, Glass
  • Physical Form: Liquid
  • Container Type: Aerosol
  • Container Capacity: 8oz
  • Grade: ESD Grade
  • Chemical Composition: 2-Propanol, 1-Butanol, Polymer, Proprietary, Nitromethane, Methanol, Propane, N-Butane
  • Application Method: Spray
  • Odor: Alcohol
  • Storage Conditions: Dry, Cool, Well-Ventilated Area, Away from Direct Sunlight, Away from Food and Drink, Eliminate All Ignition Sources
  • Flash Point: 53.1°F
  • Maximum Operating Temperature: +302°F
  • Color: Colorless
  • Primary Color: Colorless
  • Applications: ESD Environment, Janitorial
  • Package Quantity: 12CA
Techspray 1756-8S Specifications:
  • Rugged static dissipative coating
  • Surface Resistivity of 10^6 To 10^9 ohms
  • Non-ozone depleting
  • Operating temperature range up to 302°F (155°C)
  • Humidity independent
  • Superior adhesion to variety of surfaces: glass, plastic, etc
 
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Knight Shift

Knight Shift

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David_RU said:
Techspray 1756-8S is a colorless licron crystal ESD-Safe coating that comes in an 8 oz aerosol. The versatile spray provides exceptional adhesion to metals, plastics, and other surfaces,

Techspray 1756-8S Features:
  • Series: 1756
  • Product Type: Licron Crystal ESD Safe Coating
  • Material Compatibility: Metal, Plastic, Glass
  • Physical Form: Liquid
  • Container Type: Aerosol
  • Container Capacity: 8oz
  • Grade: ESD Grade
  • Chemical Composition: 2-Propanol, 1-Butanol, Polymer, Proprietary, Nitromethane, Methanol, Propane, N-Butane
  • Application Method: Spray
  • Odor: Alcohol
  • Storage Conditions: Dry, Cool, Well-Ventilated Area, Away from Direct Sunlight, Away from Food and Drink, Eliminate All Ignition Sources
  • Flash Point: 53.1°F
  • Maximum Operating Temperature: +302°F
  • Color: Colorless
  • Primary Color: Colorless
  • Applications: ESD Environment, Janitorial
  • Package Quantity: 12CA
Techspray 1756-8S Specifications:
  • Rugged static dissipative coating
  • Surface Resistivity of 10^6 To 10^9 ohms
  • Non-ozone depleting
  • Operating temperature range up to 302°F (155°C)
  • Humidity independent
  • Superior adhesion to variety of surfaces: glass, plastic, etc
Click to expand...
Interesting. Thanks. Guessing that the alcohols are providing OH groups that help with the anti-static effect. I think I posted above that when I worked in manufacturing plant down South, we would have terrible static problems in the winter, and we addressed the issue by creating a locally humid atmosphere.
 
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