Box2D - How to make a hollow circle

I would like to know how to make a hollow circle, with boxes and distance joint, something like this:

_{(so开发者_如何学运维urce: subirimagenes.com)}

I've tried it but I cant get a perfect circle, any idea? thanks

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Here is one route. Draw a regular n-gon. Below, the blue is a regular 16-gon. Then translate each edge outward radially, and connect each translated (red) edge to its original (blue):

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