4 balls together tip on one ball when rotatedOn my replicator I print with exterior support, layer 0.2. The top ball has a support structure that must be removed and should allow to print this without support, but you will need a printer that is better calibrated than mine.As with my thing http://www.thingiverse.com/thing:38459 and http://www.thingiverse.com/thing:37177, tipping is caused by friction, so use sand paper on the bottom three balls where they connect with the table to have the tetrahedron tip faster.Normally tipping goes to one of the three base balls you start with, and not to the top ball. So this does not show a full tipping behavior. I'll test a bit with different masses to see if different behavior can be achieved. Paint the balls in different colors to see to which ball it tips.The balls have a shell of 0.8 as my nozzle is 0.4, use the openscad with the scad file to change the shell thickness if you have different nozzle.While trying to find a good name for this thing, I found you can buy it as Tetra Tops, see google image search for some configurations. I actually saw this myself for the first time in a science activity for young children. Just glue with superglue 4 marbles in this configuration, and you will have the tipping effect. A really nice toy and easy to make. But if you have a printer, you can as well print it big!