# Extending or retracting a piston to the halfway

Is it possible to extend or retract a piston to the halfway by programming ?

Nope, you need a physical stop.

If you donâ€™t care about air it might be possible to retract and extend quickly and use flow limiters to hold it at halfway extended.

No, regular air cylinders (the correct term for what students call â€śpistonsâ€ť) are either fully extended or fully retracted. There is a method of connecting two air cylinders in series to create an â€śintermediateâ€ť position for a mechanism. Extend one cylinder moves the mechanism to an intermediate point, then extend the second cylinder attached to the rod-end of the first cylinder to move to a second point.

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I do have this fun video from 10 years ago. I wish I recorded more videos of it.

But a single piston that can move between 3 states.
Retracted (state A) â†’ Extended (state B) â†’ Retracted (state C)
Retracted (state A)-> Extended (state B) â†’ pause â†’ Retracted (state A)

It was an attempt at having a piston claw that could start in size without needing a dedicated flip down.

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There are three things certain in life:

1. Mentorsâ€™ dedication and patience to teach students how stuff works and properly named.

2. Studentsâ€™ desire to break out of the mould of commonly accepted solutions and do impossible.

3. Endless stream of kids coming to vex after playing minecraft and calling the pushy thing a piston.

Actually, yes. Please, tell us what you are trying to do and what extra parts you are willing to use.

If you have double acting cylinder and an extra solenoid, you can program it to vent another end of the cylinder either into the open air or into a plug, creating closed volume. Then, according to the Boyleâ€™s law, the piston will compress trapped air and stop somewhere mid-way when pressure out of the air tank and in the enclosed volume equalizes. You can regulate pressure out of the tank to tweak the intermediate position.

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An interesting (and clever) solution within the limitations of the game manual, but somewhat inexact. If we need to have an intermediate position for an industrial application, there are 3-position air cylinders available (for a price, of courseâ€¦\$200-300 for a small one): RZQ 3 Position Cylinder Standard Strokes Only

I have confidence that robotics students are smart enough to learn (and use) the actual names of mechanical devices somewhere between elementary school and graduating high schoolâ€¦itâ€™s an active choice that students make to continue using wrong terminology after learning what is proper.

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Actually I wonâ€™t use it on my robot, I just wondered if itâ€™s possible or not. Thanks for your answer.

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