karlhorton wrote:It's not quite stable like this - the open inner cube faces leave some flex, I guess.
Ah Karl, how right you are! I've corrected the note I wrote on the Geomag Wiki to read:
This is actually a relatively stable construction when using classic Geomag rods. This is because the direction that the inner cuboctahedron 'wants' to collapse is prevented by the minimum angular limit of the classic Geomag rods.To experience for myself just how unstable the inner rhombicuboctahedron could be without those last six square panels I decided to build a rhombicuboctahedron from the Geomag Kids rods and panels. And I would build it without the attached cubes, for simplicity and clarity, and to avoid the help that the Geomag minimum angular limit gave. I was expecting that the instability should be magnified because of the the larger dimensions of the Geomag Kids rods.
So first I built the rhombicuboctahedron, only inserting square panels in locations adjacent to triangular faces. As I was building it, it was clear that it was unstable, and wanted to collapse. When I adjusted the faces and gently sat the completed construction on one of its unpanelled square faces, it held together enough to stand on its own. However, when I put it on a triangular face, the thing collapsed into a shape similar to a tetrahedron!
--> I updated my
post on the Geomag Wikia with the new pix and info.