An ingenious "unfolding structure" that uses engineered, interlocking pieces that allow it to expand and contract. Invented by Chuck Hoberman who has degrees in art and mechanical engineering. Featured on The Discovery Channel's "Invention."
The unique link system is based on a mathematical principle that allows a structure to expand while keeping its shape. It is an icosidodecahedron, which means that it is a geometric solid consisting of 20 triangles and 12 pentagons. Or you can look at it as a collection of six great circles, approximated by polygons.
The Hoberman sphere expands and contracts with its hubs moving in straight lines radiating from the center. Each point of intersection reinforces the structure. If you fully expand the sphere and rest it on a pentagonal face, it will hold its shape. If you turn it slightly so that it's resting on a hub, it will quickly close.
Exhibit-size spheres have been displayed at the Museum of Modern Art in New York and can be seen in science museums throughout the United States and Europe. The largest Hoberman sphere in existence is in the atrium of the Liberty Science Center in Jersey City, NJ. It is 18 feet in diameter (when fully expanded), made of aluminum and stainless steel, and weighs 700 pounds.
A child I know recently received one of these incredible toys as a birthday gift, the boy had a hard time keeping it away from the adults at the party!
The engineer in me noticed this structure could be useful as a platform for the construction of a DysonSphere
I have one of the toys myself. When people (adults!) play with it for the first time it's hard to keep them from unfolding it, putting it on their head, and walking around like some sort of astronaut.