Can I use pneumatic cylinder as gas spring

Is it possible to use double acting pneumatic cylinder as gas spring? If it is, what requirements do we have to meet?

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That’s kind of a tricky one.

First, the simplest way you’d rig that would be to run one single tube from port to port, ideally with a flow regulator somewhere in the line. Really simple, and really effective.

The problem is that this then becomes a pneumatic device. You see, that flow regulator will tend to have pressure build up–even briefly–on one side whenever the cylinder moves. So you have a pneumatic device that is NOT in the pneumatic system, and CAN’T be vented with the main release valve. Without the flow regulator, you’ve got less of a chance of that… but still not great. R79 isn’t your friend for this particular setup. Neither is R86.

Here’s the relevant blue box, from R77, emphasis mine:
The following devices are not considered pneumatic devices and are not subject to pneumatic rules (though they must satisfy all other rules):
a. a device that creates a vacuum
b. closed-loop COTS pneumatic (gas) shocks
c. air-filled (pneumatic) wheels
d. pneumatic devices not used as part of a pneumatic system (i.e. used in a way that does not allow them to contain pressurized air)

There’s a couple of ways to do this legally. The first is to use a COTS gas shock rather than making your own. The second would be to use a spring return cylinder with its own pressure regulator, dialing it down to an appropriately-low pressure (likely pre-solenoid). You might also be able to rig a double-acting cylinder that way–you’d need to set it up to resist whichever direction the load is trying to go, and apply low pressure. Results aren’t guaranteed, though. And the third way would be to figure out another alternative. Of course, that third way will depend somewhat on what you’re thinking of doing…

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Yes the key is in Eric’s points a and d.

If you want a compression spring extend the cylinder and plug the retract port. If you want an extension spring collapse the cylinder and plug the extension port.

That way it will create a vacuum as it works and it won’t contain pressure.

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It’s perfectly possible to use a pneumatic cylinder as a gas spring! The cylinder highlighted below was plumbed to a tee between our pneumatic storage tank and the solenoid valves. That way, whenever the robot had pressure, the cylinder tried to push the climber arms up. The winch held the arms down against that force.

The advantages of an air cylinder (without a valve) instead of a gas spring in this application were:

  • It’s slightly lighter (if you already have a pneumatic system)
  • When working in the pit, with the pressure exhausted, the climber arm doesn’t keep trying to pop up when we mess with the winch. This was the main reason we did it.

The downsides were:

  • the air cylinder was bigger in diameter compared to a gas spring because of the lower pressure inside (60psi instead of 1000+ psi). That didn’t really matter to us.
  • The mechanism became less failure tolerant, since extending the arms depended on having a working pneumatic system at the end of the match.

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Gas springs can be had for very cheap from Amazon (~$15-20), if you’re worried about breaking rules with a particular pneumatic cylinder setup.

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Huh. It never occurred to me to plumb cylinders directly to storage without any controls.

Not that I’m saying we’d use it, but I do enjoy having options. Thanks!

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NP. Why add the weight of valves if you don’t need them?

Another advantage I forgot (because it didn’t really matter in our case) was that you can add one of those little inline regulators to vary the force, if you need something really precise.

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The problem is that my team is located in Turkey.

image
You should be able to find them in Turkey we’re from Brazil and we used one this season, we bought it in a general hardware store, this one is used for kitchen cabinets, if you need a bigger one they’re used in some cars trunk door

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