Are these tanks legal?

[Daniel_LaFleur]

Originally Posted by PayneTrain

I believe Allen is an LRI at various events. In this thread he's probably the foremost authority. I think it would be super if everyone else in legality threads could either feign honest understanding or step back instead of fearmonger, but I'm not a cop and can't tell people what to do.

I do not know Allens background when it comes to Pneumatics, but I do know mine as 7 years as a manufacturing engineer with pneumatic devices.

First off -- when someone asks what the failure mode is, explaining it to them is not fearmongering.
Second -- When people state that they will not use, or will only use under specific criterion, an object due to safety reasons that is their opinion, justified or not, and again not fearmongering.

I know what the failure mode is. I have seen the failure mode UP CLOSE. When I say I'm lucky to be here, I mean it.

FIRST has chosen to make these legal, that is their choice. My decision to put a box around them is an additional safety feature that I CHOOSE to implement as a safety for the audience and to protect the volumes from "robot-to-robot interaction".

If you CHOOSE to ignore my advice, that is your choice. I hope that you never see the repercussions of that choice.

JM(NS)HO

[IronicDeadBird]

Seems sketch and unmarked to the max...
If you don't know what something is why would you put it on your robot?

[JamesCH95]

To answer OP: you need the proper documentation to prove the parts' pressure ratings to an inspector. Cut and dried IMO.

Originally Posted by trumpthero786

Hmm I can't imagine using anything BUT the plastic tanks, but you have far more experience than I do. What sorts of failures have you seen in them?

I did a hefty amount of research into this a few years ago. There were a few root causes:

-The white Clippard tanks had casting voids near their threaded fitting area, weakening a key structural area
-If the threaded fittings were over-tightened cracks could be initiated in the tank
-If tanks were subjected to rapid or extreme temperature cycles they could become prone to failure (plastic shrinks more per unit temperature than the metal fittings screwed into them, generally speaking) one team had a tank burst when pressurizing a robot
-Overly aggressive mounting solutions (like hose clamps that were tightened too much) put undue stresses in the outside of tanks, increasing the chance of failure

The black Clippard tanks have improved mold design to stop voids, molded-in push-to-connect fittings, and are a more ductile plastic. They are a vast improvement over the white Clippards that were the focus of several (many?) failures. My own un-scientific destructive testing convinced me that the black tanks are considerably more robust than the white tanks.

The penalty of failure with plastic tanks is high because (if they fail) they generally undergo brittle failure, that is to say they make shrapnel. A failure in one plastic tank might cascade to adjacent tanks. Metallic tanks (if they fail) generally undergo ductile failure; there no shrapnel, or very little shrapnel.

What are the risks of any tank failing? The plastic shrapnel is sharp and could hurt someone (wear your safety glasses near any active robot) as it gets flung around 30-100 feet. Perhaps the more traumatizing danger (IMO) is the potential for hearing damage.

Having said that, there have been few, if any, failed tanks outside of the white Clippards. There have been no failed metallic tanks that I know of.

Considering the penalty of failure when using plastic tanks our team chooses not to use them. We recognize that many teams have successfully used tanks in the past. However, having done destructive testing on both plastic and metallic tanks, we have not found the compromise in penalty of failure to be worth the weight savings.

The only argument against metallic tanks that I've heard is weight. Only using metallic tanks, we have not had an overweight robot in at least 5 years, all of which used pneumatic systems. Careful selection of metallic tanks can reduce the weight penalty associated with them, and careful pneumatic system design can reduce air usage. IIRC 558 had an aluminum tank (2 years ago?) that was lighter and easier to package than the equivalent in any plastic tank.

[gpetilli]

Originally Posted by cgmv123

It's not a rule, but the introduction to the robot manual says the burden of proof is on the team to prove the legality of any part.

That said, if I remember correctly, the illegal Clippard tanks very clearly say "Clippard" on them.

The issue with the banned white Clippard tanks was that they had threaded ports on either end and if the brass insert was over tightened, the tank could (and did) fail at the threads. I cant tell by the picture, but if it uses threaded ports, as a RI I would fail it even if it were not Clippard and was demonstrated as rated to 125 psi.

Yes, bring documentation of where and what you purchased.

[PayneTrain]

Originally Posted by gpetilli

I cant tell by the picture, but if it uses threaded ports, as a RI I would fail it even if it were not Clippard and was demonstrated as rated to 125 psi.

Really hope we never go to an event where you are an LRI.

If a team has built a robot within explicit and objective parts of the rules (specifically 4.11 and R77 in your case) and you fail them anyway, you're doing an incalculable disservice to that team, Robot Inspectors, and FIRST. I guess you can try to call it an R9 since that rule in theory is pretty wide open, but its implementation is not to make illegal things that are explicitly legal.

I'm not a robot inspector, judge, referee, etc., but myself and my students can in fact read official FIRST documentation and we would really appreciate it if those with power to decide whether or not we are competing within the bounds of said documentation would also read it.

Of all of the absurdity that fills these digital walls, this kind of attitude stands heads and shoulders above in what not to do.

[Daniel_LaFleur]

Originally Posted by gpetilli

The issue with the banned white Clippard tanks was that they had threaded ports on either end and if the brass insert was over tightened, the tank could (and did) fail at the threads. I cant tell by the picture, but if it uses threaded ports, as a RI I would fail it even if it were not Clippard and was demonstrated as rated to 125 psi.

Yes, bring documentation of where and what you purchased.

This emphasized statement bothers me ( and this, coming from one whom is distrustful of plastic volumes).

1> Are these items allowed per the rules? Yes.
2> Does a Plastic Volume with threaded ports have an inherent risk? Yes.
3> Should an LRI automatically ban that item? No. (s)he should look at the implementation and decide if enough has been done to mitigate the safety risk and then make a judgment call.

It's the same when you are using sprockets and chain. It is in the design and implementation that makes it safe of not.

[AllenGregoryIV]

Originally Posted by gpetilli

The issue with the banned white Clippard tanks was that they had threaded ports on either end and if the brass insert was over tightened, the tank could (and did) fail at the threads. I cant tell by the picture, but if it uses threaded ports, as a RI I would fail it even if it were not Clippard and was demonstrated as rated to 125 psi.

Yes, bring documentation of where and what you purchased.

What testing have you done that proves that it is any threaded port on a polypropylene tank that can cause problems? Have you ever seen, heard of, or documented any plastic tank failures in FRC other than those by the original white Clippard tanks?

If I make a black plastic wheel and it happens to break apart and throw shrapnel when spun at 100 RPM should we ban all black plastic wheels? That would be the same thing as banning all plastic tanks. We specifically know that the Clippard tanks had manufacturing problems yet some people still hold it against every other plastic tank on the market, I will never understand this. I hope to keep everyone safe as well and individual teams should decide what is safe for them but the Robot Inspectors are there to enforce the rules as they are written. It would be easy for the GDC to ban all plastic air tanks with threaded fittings if they believed they caused a risk, they haven't; there for they are legal and should be ruled that way by all robot inspectors unless other factors are at play (tanks clearly damaged or showing cracks, etc) that lead you to believe they are unsafe.

[Lil' Lavery]

Originally Posted by AllenGregoryIV

If I make a black plastic wheel and it happens to break apart and throw shrapnel when spun at 100 RPM should we ban all black plastic wheels? That would be the same thing as banning all plastic tanks. We specifically know that the Clippard tanks had manufacturing problems yet some people still hold it against every other plastic tank on the market, I will never understand this.

Allen, if someone went out and did failure analysis of black plastic wheels and found the same failure mode was present in any plastic wheels, then a ban should absolutely be considered. Similar, if industrial regulations dictated that black plastic wheels should only be used when fully enclosed, the same would apply.

[MrBasse]

Originally Posted by JamesCH95

...The black Clippard tanks have improved mold design to stop voids, molded-in push-to-connect fittings, and are a more ductile plastic. They are a vast improvement over the white Clippards that were the focus of several (many?) failures. My own un-scientific destructive testing convinced me that the black tanks are considerably more robust than the white tanks...

I'll take this opportunity to remind teams that push-to-connect fittings have a lifespan. The barbs are designed to grab a hose one or two times. They are typically rated for ten cycles without failure. Anything beyond that and hose retention is a gamble that you have to determine the risks and rewards of. Since the fitting is molded in, so is the hose barb. I won't even get started on the o-rings that are non-serviceable...

[hwu24110]

If you can't see, it is threaded inside. However, I don't think I can find the receipts/documentation for what it is since I found it lying around in some bins. I think we're just going to use metal tanks.

[ToddF]

Originally Posted by MrBasse

I'll take this opportunity to remind teams that push-to-connect fittings have a lifespan. The barbs are designed to grab a hose one or two times. They are typically rated for ten cycles without failure. Anything beyond that and hose retention is a gamble that you have to determine the risks and rewards of.

This is news to me. We use SMC one touch fittings. I'm unable to find any such limitations on connection cycles. Can you point me to your reference?

[Tristan Lall]

Originally Posted by ToddF

This is news to me. We use SMC one touch fittings. I'm unable to find any such limitations on connection cycles. Can you point me to your reference?

I'm not sure of such a reference, but there are definitely many kinds of available push-in fittings, with different performance. I think it would be difficult to generalize. (Some are very tight and dig into the tubing, others are more easily releasable.)

The type of tubing (material and dimension) also matters—most styles are operable with polyurethane tubing, but there could well be non-obvious exceptions.

[MrBasse]

Originally Posted by ToddF

This is news to me. We use SMC one touch fittings. I'm unable to find any such limitations on connection cycles. Can you point me to your reference?

I worked for Parker Hannifin for several years designing products in their brass fittings division and we utilized a large group of their PTC fitting line in our product. I'd have to dig to find it if I still can, but the rating used to be on the product catalog main page. When you insert the tubing, the proper method is to insert fully and they'll tug to seat the barbs. This deform the barbs a little bit. After being done a few times the barbs no long hold a perfect shape. The metal that makes up the barb itself is only a few thousands thick and won't hold shape for long when being deformed back and forth. I'll see if I can find the spec and get back to you.

The orings just get torn up if your tubing isn't cut properly...

[Al Skierkiewicz]

Having been involved at ground zero I can tell you that not all failures were at the port, not all were due to voids and not all were due to overtightening the hardware. There were a lot of issues. One of the most catastrophic I investigated was on a robot where the team had used metal hose clamps to mount the tanks. The inside of the clamp hardware produced stress on the side of the tank and that was where the failure occurred. Think about the Pillsbury dinner roll package when you press on a seam. This team had severely distorted the outside of the tanks. Inspectors have to make the decision to allow or not allow certain devices on robots in the interest of safety to students and volunteers. Why would anyone put an undocumented part on their robot. If you can't determine where they came from and what the actual part number is, then neither can we.
Please don't use metal hose clamps when ty-wraps work as well.

[JamesCH95]

Originally Posted by Al Skierkiewicz

Having been involved at ground zero I can tell you that not all failures were at the port, not all were due to voids and not all were due to overtightening the hardware. There were a lot of issues. One of the most catastrophic I investigated was on a robot where the team had used metal hose clamps to mount the tanks. The inside of the clamp hardware produced stress on the side of the tank and that was where the failure occurred. Think about the Pillsbury dinner roll package when you press on a seam. This team had severely distorted the outside of the tanks. Inspectors have to make the decision to allow or not allow certain devices on robots in the interest of safety to students and volunteers. Why would anyone put an undocumented part on their robot. If you can't determine where they came from and what the actual part number is, then neither can we.
Please don't use metal hose clamps when ty-wraps work as well.

Not too dive off into the weeds too far... but I recall years (2010?) where zip-ties were specifically prohibited from being used to mount storage tanks. That practice does appear to be legal this year. What do you recall of past years' rules, Al?

Zip-ties aside, there are many options with which to secure air storage tanks (I like vibration damping loop clamps): http://www.mcmaster.com/#pipe-routing-clamps/=115wm73