Solenoid?

[Tom]

If price is a factor, go to your local used appliance store and ask for a clothes washer solenoid. They are dirt cheap and work well.
I know some guys here probably don't think well of them (because they are low budget) but many years ago when I first started making my own props (before I turned pro), I built 2 props using these washer solenoids. Those 2 props are in my haunt today and after 15 years, I've NEVER had one problem with them. You don't have to worry about moisture from your compressor because these solenoids were made for water.
One more thing, the cylinders in those same props are the door closers from the hardware store. Again, not one problem with them either.
But most of my other props do have the MAC valves and bimba cylinders.
Just my thoughts/experience.

[derekatronic]

Back to the original question, solenoids can be used to drive props directy. The amount of power required to actuate a solenoid goes up exponentially with the throw distance. That's why solenoids don't usually move very far. So since they're small, most people will use hobby servos to perform the same task with greater resolution. I think the only advantage of solenoids for directly driving movement is the simple control. power = actuate, no power = return.

Fun Fact: All of the facial movements in the legendary audio-animatronic Lincoln, at the 1964 World's Fair, were done with solenoids!