I really liked growe41's Atom Marble Spinner and remade it in OpenSCAD for better marble grip. You can change marble diameter and most other dimensions in customizer. Included STLs are for 15-15.5mm and for >15.5mm marbles. Of course You can use any suitable spherical objects as weights.

Used these caps.

Update 2017-06-27: You can now resize the orbits and control the atom positions in Customizer.