linear actuator release?

[man_from_brighton]

Hi folks,
I'm trying to build a release for a linear actuator to suddenly fire a weight in one direction. I have a motor attached to a long screw thread to move the weight slowly in one direction. The weight is attached to a spring and so builds up tension as it moves. Does anyone know of a sort of automated "half-nut" arrangement or similar that will spring apart allowing the weight to fly back without having to engage with the thread?
thanks.

[mklrobo]

  Hello!
I would venture a question, where permissible. Could you explain more of the
setup that you have? And if you cold make a simple "paint" pictorial, I would be more confident
in providing a resolution. Thanks..

[artbyrobot1]

I'd pull the weight down on to the spring from the sides of the weight and then have the pullers spread outward so that the weight is free to shoot out