Make Sense of the Hoberman Sphere / Circle, Linkage

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####Make Sense of the Hoberman Sphere/Circle ##### Update: New version added that makes it easy to snap the pins into the holes. I added a cut to the circular holes. This reduces the strength but helps a lot with assembling and disassembling. This move was inspired by a math teacher struggling to put things together. The Hoberman sphere is a beautiful structure (Hoberman, 1990, 1991), appealing to children and grownups alike. Mathematically, it is an extension of the traditional linkages. Taking two bars of the same length and connecting them in the middle, we get a pair of scissors, the four vertexes of which form a rectangle. Adding more and more, we get a retractable handle (or lift), a long line that never becomes a circle. However, if we bend the bar a little, say 30 degrees, the math magic happens—a retractable circle. A short analysis shows that one need 360/30 scissors pairs to make a circle. Of course, if you bend it 20 degrees, you would need 360/20=18 pairs. 3D design allows us to build Hoberman circle to help students understand and appreciate the power of mathematics and design. **The straight bar is 80mm; the bent one has two 40mm sections**. ####Steps Step One: Make a Line of Scissor Pairs Using the straight bars. It is still fun to play with it. Step Two: Make a Hoberman circle using 12 pairs of scissors (24 bars) and 36 pins. Step Three: Play around and ask questions. ####References 1. https://patentimages.storage.googleapis.com/e0/83/93/c4ddb2fa7ca5bb/US4942700.pdf 2. https://patentimages.storage.googleapis.com/9d/e1/36/24eed9959a027f/US5024031.pdf 3. https://en.wikipedia.org/wiki/Hoberman_sphere

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