[DonRotolo]

I suppose it is possible to calculate, but most of us just set it up and measure.

Let's just say you want to use pneumatics to lift your robot in the air, and it weighs 150 pounds. If you have 60 PSI to work with, you know anything less than a piston area of 2.5 in^2 won't do it (2.5 * 60 = 150). Of course, that ignores friction (which cannot be ignored).

OK now that you know the VOLUME of the pneumatic cylinders you need (cross-section times length), you can now start to calculate time, based on volume flow through the smallest element in the path (likely the pneumatic solenoid valve). How long will it take for xx cubic inches of air to flow at a pressure difference between source and chamber starting at 60 PSI and ending at zero (as the cylinder pressurizes, the pressure difference eventually goes to zero), of course while simultaneously calculating the volume (which goes from about zero eventually to maximum...

It gets complicated.

It also depends on how much air you have stored, and how much your compressor can supply.

Take two hypothetical 2" cylinders, each 30" long, using 60 PSI air and a solenoid valve for each. You have 8 large plastic storage tanks, fully charged. I am guessing it will take 15-40 seconds to fully retract those cylinders. Assuming you didn't run out all the air extending them....