Here's a circuit which implements what you want. You need a change-over pushbutton. I designed it for another Ibler a few months back, but its so useful for many projects, I just keep posting it ;-) As shown, you need a couple of relays, and couple of limit switches. The changeover push button is at the bottom right of the diagram. Arrange it, so that in the normally closed position, the load is lowered. Press the button, up it goes, until it hits the limit switch, then its stops, up. Release, down, likewise. Steve
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Thanks, I'm not sure if this will fit exactly the concept i had in mind but its likely to find its way into some part of this project.
What is "miniature" to you ?
And what is "auto"? (ie, would a spring-loaded solenoid suffice?)
Yes, I was immediately thinking of the solenoid too.
I was looking for a device that has actuates around 5-12in so, miniature may not have been the best description. Its for a kinetic sculpture idea and what I'm looking for is to have an actuator that moves when power is applied lifting a mass of a few pounds and when power is cut it fall/slides back down to its starting position.
The problem here is your requirement to "backdrive" - ie fall back to the original position, especially under control. The off the shelf actuators tend to be "locking" - they stay put when you take power off. If you changed the spec to "press the button it goes up, release the button it goes down" the answer is considerably simpler.
Ya "press the button it goes up, release the button it goes down" might work, if i went that route what were you thinking? I'd been thinking if you had a small electric motor with a small gear that is a free wheel, then have a rod lifted when the motor spins the gear and when powers cut the free wheel would let the rod fall back into into original position. I'm not sure where I might get a small free wheel that could be attached to a 9 or 12 V motor though.
Not sure about the auto retracting part, but this place has a pretty huge selection of 12v actuators. You might have to search thru it a bit. Good luck.
a spring-loaded solenoid
Electric car aerial?