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OOOH, I like the repulsing magnetic idea!  But that could turn into a game as well if you get a real nice bounce.  

Making it mechanically driven (chains, gears, screws, etc.) can allow for the addition of slip clutches and other limiting devices.  But that also makes it more complicated.

Some of the best versions of this I have seen are as simple as 4 hardened steel shafts, one set of linear bearings, and the lens mounted in a large UHMW block drilled out to slide on one of the sets of shafts.  The UHMW acts as the second set of bearings.  You can add shaft collars or other stop blocks to help prevent pinching.

I think the biggest issue may be the scale of this thing as well as the orientation.  If it is vertical then gravity is certainly an issue. and if i is large the steel shafts have to be bigger in diameter.  Never underestimate the ability
--
Erich Rose
Exhibit, Environmental and Industrial Design
807 The Living End
Austin, TX 78746
512-626-9930; [log in to unmask]

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