I have been toying around with a few ideas for better pneumatic systems for a VEX U bot for a while now and it only just now occurred to me to ask if they were even legal. I did some searching but I can’t really find any info saying one thing or the other so I thought I’d ask. In VEX U would using other compressed gasses such as Nitrogen or Co2 be legal? It would be using completely different gas tanks than the standard vex ones (probably standard compressed gas tanks you’d get from a welding supplier) so I don’t know what the legality of those tanks are.
The reason I want to do this is because using other gasses in a different form factor allows for faaar higher pressures to be stored meaning they would last much longer in matches and weigh less than just using a greater number of normal tanks. You could also just buy a bunch and have them all refilled before a competition day at a local gas supplier (or even bring an H cylinder if possible to refill on site).
The other option I was thinking of would be to use paintball tanks, they wouldn’t be as high pressure but I’d be able to fill them up by hand with a pump rather than the much more complicated alternatives for Nitrogen or Co2. Would these be legal to use as well?
It’s an interesting idea that I’d like to explore a little more but I just want to make sure it is legal to do so before I spend any more time on it. If anyone knows if that is something we could do or not, that would fantastic!
On a side note (which is pretty inline with the original question), are we allowed to use larger / different form factor pneumatic cylinders in VEX U or are we limited to the standard 2in throw VEX ones?
You are allowed any commercially available custom pneumatics. I’m not quite sure on the other gas legality, though I haven’t seen anything prohibiting it.
I don’t know everything about how pneumatics work, but legally you are only allowed 100 psi. Would using a different gas change the number of actuations that you could get out of the system? Would it affect the strength of the piston in any way?
The answer to both of these is “no”. But you guys are in college now…please quit calling air cylinders “pistons” I wouldn’t hire an electrician who calls circuit breakers “flippy switches” so why would a mechanical engineer ever call an air cylinder a “piston”? Please learn the proper terminology for your industry as a matter of professionalism.
would you explain the terminology then? What is a piston if not the vex air cylinders?
why is it called an air cylinder? that seems more confusing as the reservoirs are also cylinders of air.
I’m not a mechanical engineer and will likely never need to know this for any job I get, but I am always willing to learn if someone is willing to explain.
Well, the “piston” is a small moving component inside the air cylinder. It would be analogous with the “armature” as a small moving component inside a motor…it’s part of the actuator, but not a name for the actuator itself (outside of the VEX community, or the Minecraft game).
Reservoirs, although often cylindrical in shape, are usually called “air tanks,” and never called “cylinders of air”. In the fluid power industry, we use the terms “air (or pneumatic) cylinder” or “hydraulic cylinder” to describe the two major types of fluid-power actuators. There are some significant differences in the plumbing of hydraulic and pneumatic systems; therefore, we want to know the type of cylinder being used, either pneumatic or hydraulic.
I think this is a bit far, although, I understand your point.
I find myself calling them “Double Actions” or “Single Actions” when working with my team. I think every team develops their own lingo- and I don’t necessarily think that is a bad thing. Sure, there are professional circumstance where it would be wrong to say “piston.”
When my team first started, we didn’t know the name of the nut driver, and we called them “Blue thingys,” and it became an inside joke. Even now, with a collegiate team, I still call them that sometimes.
Yes standard nitrogen tanks you’d get from a welding supplier would be a little over 2000psi but would be regulated down to a lower pressure. Assuming I had a way to regulate it down to 100psi and lock it there, this method would technically follow all pneumatic guidelines in the rules correct? Either way, thank you for providing some clarification on this, I have a lot more ideas to run through now!
Also to make a note on this, yes, I do understand the correct terminology for this, however in this instance, calling everything by it’s grammatically correct name would just be overly confusing when I am just asking a question. If you go to any welding or gas supplier, they are simply called gas cylinders or tanks (sometimes even bottles), hence the name H cylinder for the huge ones and the vast majority of people call them that. Nobody calls them reservoirs in that field so to avoid any confusion, I was just using the most logically understandable terms in this setting. If I were in a professional environment, surrounded by other mechanical engineers who also understand all of the correct terminology, yes, I would use it.
In my opinion, it is better to use the terminology of piston. Although it isn’t the proper name, most people (including those who are not engineers) will understand what you are talking about. Some judges that are volunteers might not understand what a “Single acting air cylinder” is, but others might. It is just more universal to use the word piston. Should students be taught to know and use the proper terminology? Yes. Is it usually easier to say piston rather than air cylinder? Yes. Should students (college or not) be expected to always use the proper terminology? No, but they should use it most of the time. This is my opinion on this, I am in no way against using the proper terminology, I (and some other people) believe that it is easier to say piston rather than air cylinder.
So that leaves propane tanks out, since their pressure ranges from 140-175 PSI (depending on the temp outside the tank). And the use of “tank” is correct, that is the industry standard term. (Ya’ll can now say 'Propane and propane accessories" in your best Hank Hill voice)
I’m still confused on this. Why would you use nitrogen over air on the robot. You could have the 2000 psi tank that you could use to refuel during matches, but you wouldn’t be able to have the 2000psi tank on the robot during matches. I’m not understanding what the benefit would be.
Not sure what the point is of this tangent on terminology when the actual questions that OP put forth are unanswered…
So the rules don’t say anything about “regulating” the pressure to a specific value, and that’s intentional.
Let’s look at VUR13 a:
So, the rules state that the maximum pressure any pneumatic device is charged to is 100psi. If you have a tank running at a higher pressure which is then regulated down to 100psi, then the pneumatic system is still illegal because it is charged beyond 100psi. With this established, let’s look at your original questions:
The maximum pressure allowed on the robot is 100psi, so this is not legal.
Paintball tanks themselves are not illegal, however it is not legal to use their expanded range of pressures beyond 100psi so the added weight over a standard plastic/aluminum reservoir is likely not a good trade off.
This question can be answered pretty comprehensively by VUR13.
Now, this question I am unsure of the answer for. While I am unsure of what exact benefits could be derived from using these gasses over simple compressed air at 100psi, you could ask a question on the official Q&A if you still want an answer.
In certain closed and/or critical pneumatic systems (also automotive racing folks often fill their tires with pure nitrogen), we sometimes use pure nitrogen for the benefits of cleanliness and corrosion/oxidation prevention, because pure nitrogen is completely dry and contains no oxygen. It doesn’t provide any performance benefit. Breathing air is about 78% nitrogen, and both air and nitrogen (real gases) behave almost identical to ideal gasses (as used by the ideal gas laws) when used at typical pressures and temperatures.
one other benefit that I do not think was mentioned is the fact that N2 gas molecules are larger than oxygen molecules and are used in tires not only to prevent corrosion, but to prevent leaking and to maintain pressure. MTB shocks also use nitrogen to fill their reservoirs for the same reasons. I guess nitrogen could potentially be used to minimize air loss between matches but the effects would be negligible and would only really be apparent in long-term air storage. I suggest possibly testing and recording your results?
I apologise for any mistakes, I did not research further into the uses of different gasses.
Yep. On the scale of vex, a well tuned air system will have no problem leeking. I would leave the bot over the weekend and I would come back and the bot would still have over 90 psi. When you can fill up the bot with air 5 minutes before a match, this is no concern.
One other consideration against, you may end up with facilities where tournaments are held that might be VERY skeptical about bringing in a large nitrogen or CO2 tank that you’d use to refill from. At the very least, I expect that you’d be laying a lot of groundwork ahead of time with EPs to make sure there’d be no problem; and then what do you do if they say no?
How much does a 6000 psi nitrogen tank weight?
Storage Cylinder 6,000 PSI - August Industries Inc.
This 6,000 PSI storage cylinder will allow the user to bank air at 6,000 PSI which is ideal when your needs are 4500 PSI. This storage cylinder weighs 195 pounds empty and is 55 inches tall.
I doubt anyone would bring a full size tank if they utilized compressed nitrogen. You can get much smaller (like 18” tall) and easier to handle tanks that could store a years worth of gas for VEX purposes.
Of course this is basically moot because there’s no point to using nitrogen.
I will also say that there would need to be safety considerations regarding the high pressure tanks themselves and how they are handled if a team chooses to use them to fill their robot. If mishandled they can very easily become missiles…
Honestly it would take a lot of convincing for me to allow a team to use one of these to fill up their robot at an event.
