Pistons only halfway up

[dtengineering]

You should also have some flow regulators that can slow the flow of air into smaller pistons.

Consider that air roughly follows the ideal gas laws of PV=nRT. P is the pressure, V is the volume and n is the number of moles of the gas. R is a constant and T, the temperature, is also roughly constant.

So as you put more moles (n) of gas into the cylinder, either the pressure or the volume must increase. Normally we extend a cylinder all the way... the pressure increases, forcing the piston outward, and allowing the volume to increase.

If, however, you put just a little bit of air into the cylinder, then as the volume increases the pressure will drop, until your piston position finds equilibrium with the applied load. (The pressure in your cylinder pushing on the piston will be balanced by the force applied to the piston.)

This sounds easy until you try to do it, and what works in your shop (at your altitude, temperature and humidity) might not work at your competition venue without some careful tweaking.

This is naturally quite a bit different from a hydraulic system as air is a compressible gas while hydraulic fluids are specifically chosen to be as incompressible as possible.

For precise, reliable positioning you may wish to consider some from of linear actuator... or perhaps using one of those lead screws that come in the KoP (longer ones are available) for something other than entertaining that team member who really, really, likes turning the lead screw up, and down... up and down...

Jason