The famous expanding and contracting ball toy that also makes excellent structural support for whatever sparse scaffolding you need. Basically, if you can design it as a geometric solid, you can probably make a collapsible version with this. In a pinch, also doubles as a jack or a reacher-grabber claw.I was looking to build a NautilusX model http://en.wikipedia.org/wiki/Nautilus-X and realized that Thingiverse didn't even have a Hoberman sphere library. It uses one-way snaps might be useful for other projects too.I'm not nearly clever enough to invent the Hoberman sphere. Thanks to Charles Hoberman for the original concept and helpfully detailed drawings.Print out lots of copies of the plate. Join those copies together. The arms snap together so no need for glue or bolts or anything silly like that. Make sure you have the arms facing the right way, because they don't unsnap together very easily (see picture). Join three or more arms together with the rings so that they can all rotate independently on different axes.If you're making an icosahedron (the simplest "sphere"), you'll need 30 plates. Any more then that and you will probably need to adjust arm lengths, and the positions of the pins.Until I get enough arms printed to start seriously assembling, this will be a work in progress.