building an energy conserving pneumatic system

[Rafael2215]

Hi,
We were wondering whether it is possible to build a pneumatic system that conserves the air it's using, meaning that after the first pressurization of the tanks, made by the compressor, there will be no need for any more pressurizations for the remainder of the match, that is you start the compressor only once at the begginnig of the match and stop it when the pressure in the tanks reaches 115 psi (this being achieved by having the same volume of air leaving the piston at one end entering the piston at the other end simultaneously).
If it is possible, can anyone shed some light about how to build such a system?

Thanks,
Team 2215

[martin417]

What you are describing is perpetual motion, and it is against the law (physical law that is). If you have a very small amount of work you want to to during the match, the initial fill might last, but you can't go forever.

[JamesCH95]

Use the smallest stroke and bore pistons you can get away with, actuate your pistons at the lowest possible pressure, and if you don't need a huge amount of force to return your pistons consider a second circuit at an even lower pressure to return them, or use spring-return pistons. Also, use tons of leak-check (soapy water) to make sure your system has as few leaks as possible! It is nearly impossible to have a system that's completely leak-free, however.

[Al Skierkiewicz]

Does not the regulator vent to maintain low side pressure?

[MrForbes]

Originally Posted by Rafael2215

If it is possible, can anyone shed some light about how to build such a system?

It's easy, just make it so that the pneumatic system needs to do no work. That means, don't put any cylinders in it. Then it will maintain pressure.

But if you want the system to move something on the robot, then the air pressure in the storage tanks will drop, and you'll need to refill them with the compressor.

What pneumatics does is use a motor (the compressor) to do work remotely (the cylinder) by using air flow.

If you don't let the air out of the other end of the cylinder then there will be no pressure difference in the cylinder, so the piston won't be able to exert any force.

[Tom Line]

Originally Posted by Al Skierkiewicz

Does not the regulator vent to maintain low side pressure?

Al's channeling Yoda

The only type of pneumatic system that doesn't use air would be along the lines of using the air as a spring - such as a pneumatic shock. You would have to use a motor to then wind a load back against the air.

You can't get something for nothing. It's thermodynamics.

[dtengineering]

While physics prevents you from getting more energy out of a system than you put into it, there are ways that you can conserve the energy in a pressurized system by extracting that energy more efficiently.

One example is the double (or triple) expansion steam engine http://en.wikipedia.org/wiki/Steam_e...ansion_engines where the exhaust from the high pressure cylinder is used to feed a lower pressure cylinder. I wouldn't recommend this for an FRC robot's pneumatic system, but it is interesting to know about from a themodynamics standpoint.

Jason

P.S. While I was looking for a good link to explain multiple expansion engines, I stumbled upon this site: http://www.animatedengines.com/index.shtml where someone has taken a lot of time to show off how a number of different engines (including several variations of Stirling Cycle engines) work.

[JamesCH95]

Annoying answers aside, you can get about 12 shots of a 3/4" diameter, 5"stroke piston before the storage tanks drop below 60psi, starting at 120. So if you need pneumatics to perform a one-time action like lift an arm up, you might not need the compressor.

Edit: for example, to improve efficiency on our kicker mechanism, only 2 of the four pistons are charged to return the kicker, while four are charged to deploy it, reducing air consumption per shot by 25%. We might even dial it down to 1 return piston if that turns out to be adequate.

[MrForbes]

Originally Posted by Rafael2215

(this being achieved by having the same volume of air leaving the piston at one end entering the piston at the other end simultaneously)

I think the "annoying answers" were to this part of the question.