First off, I already know the answer to my question: Can we use 1/4" OD copper tubing for the high pressure side of the pneumatics system. The short answer is No. No explanation, other than it’s not listed in the KOP. Fine.
Please explain though, why. The copper tubing has a working pressure rating 1195 PSI, vs. the poly tubing that’s “approved” that has a working pressure of 125 PSI. TECHNICALLY, R82.E (E. Additional pneumatic tubing, with a maximum 0.165 in. (nominal) inside diameter, functionally equivalent to that provided in the KOP,) the copper IS functionally equivalent, and superior to the KOP (IMO). 1195 PSI vs. 125 PSI. I will say that the nominal ID is slightly above that of the poly tube, but that is more to its nature of being a more rigid material rather than a flexible material.
On the surface, it seems that the copper tubing would be safer, as it can handle higher pressure.
Now for the discussion portion…
Obviously, with this year’s theme, copper tubing most definitely fits. See the picture of what I was starting with. I was planning to pipe the entire high pressure side with copper tubing.
All of the lines coming from the manifold would obviously be the poly tubing, so they had flexibility going to the shifters, cylinders etc. That’s just common sense.
I have a hard time understanding the problem with the non-movable parts not being a rigid tube.
Is it due to the fact that the connections need more care to assure proper fit?
Is it because there are more parts required? (ferrules, compression rings, etc.)
Is there concern for the copper lines being caught and pulled? The same thing can happen with poly lines, and I would think they are even more prone, since they move.
Is it that FIRST takes cost into consideration, since the copper tubing, brass fittings and tools to work with it are more costly than the poly tube?
Part does’t need to be in KOP. I don’t believe there is specific rule about it, I may be wrong. One reason I wouldn’t go for copper is weight and flexibility.
“Functionally equivalent” does not mean “can perform the same function as”. Lots of things can hold compressed air, that doesn’t mean they are “functionally equivalent” to rubber pneumatic tubing. In this case, the tubing differs in weight, size, rigidity, material… Very clearly not “functionally equivalent” parts!
In a general sense, the reason the pneumatics rules are so restricted are so that pneumatics systems are (1) for sure safe and (2) easy to inspect. If there’s only one kind of legal tubing, and it’s something that FRC knows is safe and will work, it is much easier for everyone to use and inspect it.
One thing that is never allowed are custom pneumatics parts - they cannot be cut or modified whatsoever other than as specifically allowed in the rules. Creating copper tubing for your pneumatic lines would involve teams creating their own custom pressure vessels - these obviously cannot be rated and their safety cannot be verified by inspectors. This is an unacceptable risk to allow, even if most teams are surely doing it right and the error rate is low.
All of that said, this isn’t something FIRST is going to change; no amount of arguing is going to fix this one, so in this last week of build, I really wouldn’t waste your time getting invested in a solution that’s clearly illegal and has been for season after season.
The why is that it is not listed in the allowed components for pneumatic system.
Since I am not the GDC I can only speculate as to the reason. Here goes: Pneumatic has to potential to release a lot of energy rapidly. Robots are being designed by people who are learning and don’t necessarily understand all the risks. Robots are inspected by people with varying levels of experience. I think the GDC is trying to keep the components down to a manageable level with all that in mind. They have gotten less restrictive over time. They use to limit air storage on the robot, valves to a mythical Cv number, required a component working pressure for valves that drastically limited choices. So things are improving.
Rigid tubing on a moving robot that is subject to collision forces is asking for problems. Especially copper tubing, which is a relatively soft metal. Easily fatigues with repeated bending. If the copper tubing bursts, there is probably not much risk of a lot of metal flying, but there could be a few pieces of metal.
You do realize that you can no longer buy those tanks that would fail as described in your link and that the ones in the picture are the smaller volume white tanks that are legal this year and last.
If you really want the copper or brass look, just get some tubing that’s big enough to go around the approved plastic tubing. That’s what we were planning if we did a modest amount of pneumatics. (We’re all electric this year.)
I was aware the tank could no longer be purchased but I couldn’t tell that the tank was different from the defective ones. Looking at the picture again, I can see the shorter size.
Edit: Jeez, how big did I think the compressor was?
Have you asked Q&A yet? My answer doesn’t count, but copper tubing and fittings are functionally equivalent and safe for the application. I don’t use it in FRC because it doesn’t seem to be a good application due to weight and cost.
So here is a little more fuel…
All copper tubing is not made the same. If it is not a pneumatic component, marked as such and used in accordance with manufacturer’s recommendations, it will fail under pressure. Copper tubing failing, under pressure, can cause considerable human damage.
I would be concerned when seeing copper placed over plastic tubing because of the potential sharp edges where the tubing is cut to length. Those edges could cut into the tubing and cause early failure.
A lot of craft stores sell thin copper tape (real metal not plastic) on rolls with sticky backing. Some of that wrapped around your poly tubing would give the same look.
Please don’t do this. In addition to the reliability issue that Al pointed out with sharp edges, hiding the pneumatic tubing will make robot inspection more difficult. Robot inspectors prefer to be able to read the screen-printed rating on the tube.
It may also make it more difficult for you to find leaks and troubleshoot pneumatics issues.
Please treat all pneumatic parts as sacred, including tape, paint or even covering. Don’t make your inspector’s job difficult just for decorations sake and don’t make the LRI make a tough decision.
“Functionally” they are the same thing. They both hold pressurized air, and allow air to pass through.
Is this not exactly what we do when we cut poly tubing? Are we not creating “custom pressure vessels?”
I’m not trying to get it changed. I’ve already resigned to the fact that the copper tube isn’t legal. I said that from the get go. It’s ok though, just disappointing. I was simply looking for thoughts as to why.
This I can understand. If you were to get cheap copper, that isn’t rated for air pressure, it could cause serious safety issues. And having to worry about compliance certificates for items that can support air pressure opens a whole other can of worms. I get that. However, if a team is willing to go through the extra effort to obtain the proper tubing, gather the proper certificates (I have to do this all the time for that darn CE symbol, but I digress…) wouldn’t it suffice to the LRI? Now I also understand that the LRI and the RIs are just normal people. It’s not their responsibility to know how to identify different types of copper tubing, and for that reason alone I Can understand FIRST’s rationale.
As I said before, this was just something to get thoughts about. I’m not setting out to change the world, or even the Sacred Realm of Pneumatics of FIRST. Just some opinions and how others view the whole sordid pneumatics cadre…
Now, to go listen to Clockwork Angels and think about that Headlong Flight into Week 1…
It may be possible to get copper tubing added, with all the required certificates. The cost of doing so is that it will increase the amount of training that the Inspectors must go through. The greater the workload you place on the volunteers, the more likely they will burn out. Most of the people needed to run these events are volunteers. Please try to make their jobs easier where possible.
Copper can work harden and crack if flexed enough. Your robot would have to be considered a high-vibration environment. The overall reliability of your pneumatic system is likely to be reduced if you use hard lines.
It is cool to see people thinking outside the box. A good engineer knows when to think outside the box and when to think inside the box.
