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Originally Posted by KenWittlief
I think you missed part of the description.
you include a clutch or locking mechanism on the joint, so once the arm is in the proper location, the clutch locks, holding the arm rigid. Unless you add enough weight to the end of the arm to overpower the clutch, its not going to move
and with this approach you dont try to control the pressure in the cylinder, or to apply pressure to both ends - you use the cylinder in the normal configuration, with the little flow restrictors to slow down their movement.
The clutch is in the feedback loop, not the valves. Once the arm has moved to the right position (up or down) the clutch locks and holds it against the pnuematic pressure, and against any added weight to the end of the arm.
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I have tried this and it works! There are nifty off the shelf cylinders with pneumatic cluthes built in for exactly this application but they are of course not FIRST legal.
It might still be nifty to use a closed center valve in addition to a locking mechanism. By pulsing it on and off at different duty cycles, you could move at different speeds. Another strategy is to use more than one valve to control a cylinder. Each valve has it's flow restricted to a different extent.