Expanding Polygon Linkages


As part of 6.S080 Mechanical Invention through Computation, I had to make an expanding polygon linkages based on the geometry explained in lecture. I picked a very simple octagon, because I wanted to try looking at the stress patterns using photoelasticity — which is a way to visualize stress patterns in a transparent material using polarized light.

It’s actually pretty easy to do at home, because most computers have a polarizing filter on their screens, and 3D glasses for movies now mostly use polarizing lenses. So you put the transparent material in front of  a white computer screen, through on some 3D glasses, and you can see the stress patterns!

Unfortunately my camera didn’t pick them up as well as my eyes, and the overlapping parts make it complicated, but you can definitely start to see them appear. I put a bar across the middle to lock the linkage at one point.

I also experimented with leaving some joints out. Then you get the interesting effect of allowing one side to move independently of the other, which is pretty cool.




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