Destructive Air Tank Testing

[DonRotolo]

Originally Posted by Andy A.

All the tanks were pressurised to 120psi (regulated output of a shop compressor) then struck with an air rifle pellet to induce the failure. It turned out to be remarkably consistent and reliable (well, as reliable as my aim!)

The clear call for acton is to ban air rifles from competition!

No, seriously: Thanks for doing this. The key take-aways are that shrapnel from a tank has a lot more force than most folks believe (and can imagine!), AND that a relatively minor impact can be catastrophic.

At MAR Clifton last weekend several teams with 'exposed' tanks (black or white) were asked to add some sort of protective covering to their tanks - not to contain shrapnel but to help avoid impacts that could damage the tank.

[Tristan Lall]

Originally Posted by JamesCH95

I think we might also try to make a metal tank fail, but that's a whole other ball of wax...

If you can spare one, do it, to demonstrate the difference in failure mode.

[Andy A.]

Originally Posted by Tristan Lall

If you can spare one, do it, to demonstrate the difference in failure mode.

We've got metal tanks galore, in fact. We had meant to test one at the same time as the plastic tanks but ran out of daylight and, in any case, I'm fairly confident the air rifle we had wouldn't have caused anything more then a dinging noise at the range we were shooting at.

We're hoping to do a second round of tests in the near future and we'll include a metal tank or two while we're at it. Causing that to fail will probably require an actual firearm which, while entirely doable, is another level of complexity. We'll chew on that one.

[Max Boord]

First thank you for doing this type of testing. 1523 has always used metal tanks and are interested in seeing how they fail. For round 2 can you guys film it? I find it hard to visualize the amount of energy stored in a tiny plastic air tank causing the amount of damage documented in these cases. As for debris reduction methods:
1. a heavy sock zip tied around the tank
2. a layer of screen enclosure material wrapped around the tank (its tough and will let more air escape than bumper material)
3. electrical tape
4. a thin piece of sheet metal wrapped around the tank.
5. anything else quickly retrofitable for teams close to the weight limit and who have another event.

[JamesCH95]

Originally Posted by Max Boord

First thank you for doing this type of testing. 1523 has always used metal tanks and are interested in seeing how they fail. For round 2 can you guys film it? I find it hard to visualize the amount of energy stored in a tiny plastic air tank causing the amount of damage documented in these cases. As for debris reduction methods:
1. a heavy sock zip tied around the tank
2. a layer of screen enclosure material wrapped around the tank (its tough and will let more air escape than bumper material)
3. electrical tape
4. a thin piece of sheet metal wrapped around the tank.
5. anything else quickly retrofitable for teams close to the weight limit and who have another event.

Please send tanks!

Also, a video of the tests will be out shortly... editing is a tedious process.

[JamesCH95]

Originally Posted by AllenGregoryIV

There are plenty of competitive teams that don't use a mill, lathe, or welder (I have never had a student weld anything on team I have been on in 12 years of FRC, doesn't mean I don't think other teams should do it). We needed to use light weight tanks just as much as we needed to use aluminum axles instead of steel. There are places to save weight but buying plastic air tanks is easier. Also AndyMark sales a variety of air tanks, some of them are from Clippard and others are not.

Those are just for-instances. Don't take it too literally. Any tool used in a shop has the potential to be dangerous, and yet every team uses them because they have to use tools to make a robot. No one has to use plastic air tanks if they choose not to.

It is easy to buy a different component to save weight, so I swap out motors. An RS775+CIM-U-Lator is 1lb lighter and more powerful than a mini-cim, for example. There are lots of places to save weight. I personally could not stomach the thought of a plastic tank on my robot causing anyone harm, so I choose not to use them on any robots that my team makes.

[AllenGregoryIV]

Originally Posted by JamesCH95

Those are just for-instances. Don't take it too literally. Any tool used in a shop has the potential to be dangerous, and yet every team uses them because they have to use tools to make a robot. No one has to use plastic air tanks if they choose not to.

It is easy to buy a different component to save weight, so I swap out motors. An RS775+CIM-U-Lator is 1lb lighter and more powerful than a mini-cim, for example. There are lots of places to save weight. I personally could not stomach the thought of a plastic tank on my robot causing anyone harm, so I choose not to use them on any robots that my team makes.

And that is perfectly fine but the important part is you shouldn't necessarily assume that every team feels the way that you do, I have never used a plastic clippard tank on a robot and probably won't, I however have and will continue to use the Pneaire tanks until I see evidence that the risk is too great. Andy Baker once said something about Ice Cream and it still being good even if it wasn't your favorite flavor and that it might be someone elses favorite flavor.

[JamesCH95]

Originally Posted by AllenGregoryIV

And that is perfectly fine but the important part is you shouldn't necessarily assume that every team feels the way that you do, I have never used a plastic clippard tank on a robot and probably won't, I however have and will continue to use the Pneaire tanks until I see evidence that the risk is too great. Andy Baker once said something about Ice Cream and it still being good even if it wasn't your favorite flavor and that it might be someone elses favorite flavor.

That's fine, as long as their favorite flavor of ice cream doesn't put shrapnel in a bystander's face, or my face. When someone else's choice puts an innocent bystander (in this case refs, human players, announcers, emcees, the audience, etc) at risk, that's when I start to have a problem.

[JamesCH95]

A quickly-edited video!

https://www.youtube.com/watch?v=Oea-...ature=youtu.be

I also updated the OP with the video link.

[ToddF]

Originally Posted by JamesCH95

When someone else's choice puts an innocent bystander (in this case refs, human players, announcers, emcees, the audience, etc) at risk, that's when I start to have a problem.

That's why the uncalled G28 penalties are so upsetting. The risk with these tanks isn't that they will fail under normal circumstances. It's that they will fail when damaged by another robot. This is NEVER supposed to happen. It is against the rules to deliberately touch another robot inside their frame perimeter. If the tanks are mounted inside a robot's frame perimeter, they should be completely safe. Unfortunately, the style of game this year has resulted in a lot of people just shrugging their shoulders and accepting repeated G28 violations has "just part of the game", or "accidental, not deliberate".

I contend that these G28 violations are just as accidental as when a drunk driver gets behind the wheel and "accidentally" kills someone. When they get behind the wheel, the drunk driver assumes responsibility for the results of that action. Similarly, a team who drives a robot around the field with appendages hanging over their bumpers should be FULLY ACCOUNTABLE for the penalties which result. I knew we were heading down a slippery slope when the game design committee legitimized bad behavior by changing the rules to allow robots to extend outside the field. Rather than penalizing teams creating a safety hazard, they made it acceptable for teams to drive around with their appendages hanging out. This has led to the current culture of defenders choosing to extend their appendages, ram them into other robots, and cause damage, then saying "Whoops. It was an accident."

As we see from these tests, not enforcing the rules can have serious consequences. It's not just the air tanks that are a possible hazard. The batteries we use are just plastic boxes that contain acid. There are wires in the robot that when shorted together can cause fires. There are SAFETY reasons why G28 exists. Teams should be living in desperate fear of touching another robot inside their perimeters, and the penalties this would incur. This year, starting with the rule change allowing robots to extend outside the field, we've been more and more accepting of safety violations. I, for one, think this is a bad thing.

[Siri]

Originally Posted by ToddF

That's why the uncalled G28 penalties are so upsetting. The risk with these tanks isn't that they will fail under normal circumstances. It's that they will fail when damaged by another robot. This is NEVER supposed to happen. It is against the rules to deliberately touch another robot inside their frame perimeter. If the tanks are mounted inside a robot's frame perimeter, they should be completely safe.

I'll abstain for the debate about how I'd like to see G28 called, but just as a note, your statement is not the rule: I've seen an entirely non-trivial number of alliance partners damage each other's robots. Moreover, legal bumper-bumper contact pushes many a robot into the side of low goal, the bars of which can you a number on many robots. Essentially, for teams to withstand expected legal damage, they still need to have their tanks relatively* well protected. Just something to remember.

*I do not know what that means specifically, which is why I'm reading this thread. Thanks 95!

[JamesCH95]

I agree with everything you said Todd.

Though plastic air tanks are different than the battery and an electrical in that they have a much safer alternative, and a tank failure is arguably more dangerous than a fire or a battery rupture.

A ruptured battery will fizzle and spew acid all over the field, and then be contained with a spill kit. An electrical fire with burn a robot(s) and/or the field, and then get put out with a fire extinguisher. An exploding tank sends shrapnel flying.

Like I said, I agree that robots violating G28 could cause tank failures, and that's not okay. But, just like laws that discourage negative actions, laws do not prevent them, nor do laws prevent accidents. As the FIRST community we have a choice to try a multitude of fixes, or choose an intrinsically safe solution.

As an aside, in our second QF match at GSDE we were hit with a G28 technical foul when our bumper rode up on top of another robot's bumper. No contact inside either bumper zone, certainly no contact of any consequence. It's tough to ride that fine line in calling technical fouls...

[AllenGregoryIV]

Originally Posted by JamesCH95

That's fine, as long as their favorite flavor of ice cream doesn't put shrapnel in a bystander's face, or my face. When someone else's choice puts an innocent bystander (in this case refs, human players, announcers, emcees, the audience, etc) at risk, that's when I start to have a problem.

True, I didn't elaborate on the example nearly far enough. We all like ice cream, and about 4 years ago a few people started buying Company A's no fat vanilla ice cream. They could eat a lot of ice cream and not deal with the negative calories. Company B who had been selling us ice cream for a long time decided to also make a no fat vanilla ice cream. The problem is Company B's no fat vanilla ice cream has manufacturing problems that were quickly discovered and Company B has offered to replace all there no fat vanilla with there full fat vanilla free of charge to anyone that has bought it. Some teams never switched to company B's no fat vanilla they have been going out and buying Company A's ice cream the whole time, and it has never had any problems. Company B has just recently released a no fat chocolate ice cream. The chocolate ice cream so far seems to be pretty good it doesn't seem to have the manufacturing issues that plagued company B's vanilla ice cream. Lately people have been suggesting a ban on all no fat ice cream or at least on all vanilla no fat ice cream when really only one type of vanilla no fat ice cream has been shown to have issues.

[BBray_T1296]

I remember Clippard responding to the explosions last year by stating that when fittings were ***Properly*** installed, they were unable to get the tanks to burst as high as 600PSI

Properly being with correct teflon taping, and not overtightened until cracking

[Oblarg]

Originally Posted by BBray_T1296

I remember Clippard responding to the explosions last year by stating that when fittings were ***Properly*** installed, they were unable to get the tanks to burst as high as 600PSI

Properly being with correct teflon taping, and not overtightened until cracking

I'm absolutely certain that plastic tanks can be used in a manner which is entirely safe. But this is a high-school competition, not a professional engineering work environment, and I have serious reservations about hardware with such a dangerous failure mode in this context.