# [2009-04-01] POV-Ray oloid two-disc roller

Oloids give me a serious nerdgasm. I have this long-standing plan to get one 3D-printed. But first, I needed a good quality 3D-model, which I couldn't find anywhere on line. And the shape is actually pretty difficult to sculpt in all the 3D modelling packages I've tried (SketchUp, Blender). I finally decided generating the model by hand was too much work, and started to look for a utility that would take a set of points in 3-space and produce a 3D model of their convex hull. Such a utility is qhull, which works like a charm from the command line. The 3D points (512 along the circumference of each of two orthogonal circles) were calculated in Google Spreadsheet, then cut-and-pasted into Notepad to generate a text file which was piped to qhull at the Windows Vista shell command line as:

type oloid_points.txt | qconvex m TO 'oloid_hull.txt'

The resulting Mathematica-style mesh was readily converted to a POV-Ray mesh using the Notepad search and replace function. All you have to do is replace the word "Polygon" with the word "triangle," strike out a few commas, and interchange some curly and angle brackets. The resulting includable mesh file is here. The model has radii of 1 POV-Ray unit, but of course it can be scaled to any size you like. The distance between the circle centers is the square root of 2, which results in an oloid that has a constant center of gravity when rolling.

Thanks to Sam and Thomas Ettinger for converting this mesh to a printable .STL file.

last modified 2009-04-10