Wednesday, December 1, 2010

Rattleback twins

On Tuesday evening I saw a model of a Rattleback posted on Thingiverse. A traditional rattleback reverses direction when it's spun in a clockwise direction.

I made two models, one with the mesh reversed so it would respond to a counter-clockwise spin. Unfortunately the models were too 'tall' so they tended to tip over instead of spinning. A conventional rattleback, at lower-right, is only half as thick.

Since the model was just too thick, I used SDMove (the SD300 build software) to reduce it 45% in the Z axis and built another set. The new model, shown in red, was much more functional. But it had a flat spot due to the layers in the Z axis, so it wasn't as good as it could be.

So I built a third set using the same mesh, but oriented it to be built on its long edge. This exploited the SD300's excellent XY axis resolution to give smooth, curved contours. (FDM users employ the same strategy.)

Now I've got a left-handed and right-handed pair of rattlebacks, one which reverses clockwise and the other counterclockwise. They're still not optimized, but it's probably as good as it gets by just tweaking the mesh rather than re-contouring the source data.

I uploaded the modified meshes back to Thingiverse for the benefit of other users. Maybe someone will refine it further.

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