Usign a 2-1/2 bore, 24" stroke pneumatic cylinder.

[GeeTwo]

Originally Posted by EricH

The thing with pneumatics is that you want to use the smallest cylinder you can get away with, in general (at least in FRC).

It depends on whether you want fast or minimal air use. If you need fast, (e.g. for a launcher), you will have to use cylinders that are larger than "you can get away with". If you have enough time to do it efficiently, you want to use a minimal -sized cylinder.

If going fast, the limiting factor is how fast air can go through the 1/8" NPT ports (or perhaps smaller) on your solenoid valves at the "real" working pressure you will use. This will be much less than the 60psi on the supply side of the valve, probably more like 15 or 20 psi to optimize power through a 1/8" NPT orifice.

Edit2:
Amplification and correction: The flow rate through a 1/8" orifice with 60 psi on the supply side and up to about 20 psi on the working side is about 13 scfm. At 30 it's about 12 scfm, at 40 psi, it's about 11 scfm, at 50, about 8, and at 55 about 6. Calculating the actual rate of volume change and multiplying by the gauge pressure, fastest work gets done between 20 and 40 psig. If you want it to work fast, design so that the job is done by 40 to 50 psi.
/Edit2

Originally Posted by dradel

I was going to suggest mounting the cylinder up side down, or backward from how they are typically mounted. That way the rod won't come into play

That won't help. The rod comes into play whenever the cylinder is made shorter, no matter whether the rod or the chamber is at the fixed end.

Edit:

Originally Posted by dradel

I was referring to the rod affecting the power not the speed.

So was I. When pressurizing the return stroke, the net area that the air is pushing against does not include the rod, independently of the orientation of the cylinder.