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

[s_forbes]

Originally Posted by Chris Fultz

The 2.5" cylinder has 160% of the volume of the 2" cylinder, so it will take about 160% of the time, assuming you have the available volume of stored air.

I think this is the part to pay attention to. A 2.5" cylinder uses up 160% as much volume as a 2" cylinder of the same length, so the robot needs to store 160% more air, and it takes longer to shove all that air through the port of the cylinder.

Even though a 2" cylinder will extend faster, you can still make a 2.5" cylinder work. You just need to solve those two issues.

1. Storing more air - This is easy if you have the space, just add more tanks. You can get some really big ones if you look around.
2. Shove the air in fast enough - There are lots of tricks to increase the flow rate of air into a cylinder. Get a high flow solenoid (mcmaster 6124K511, for example). Decrease the amount of tubing between the solenoid and the cylinder - you can mount the solenoid right onto it if you use the right fittings. Add air tanks right before the solenoid so air doesn't have to go through the regulator. You can make these things flow really fast.

Interestingly, we found a use for our 2.5" bore 24" stroke cylinder this year... it had previously been sitting in our back room collecting dust. We used it to measure the flow rate of the solenoid above using our pneumatic layout. (Useful data for some other minor mechanism on the robot this year )

The cylinder in the setup below extended in 0.170 seconds (but no load other than the mass of the cylinder rod)