Yes, yes, the CAD I'm using is :cough: Javascript. OpenJSCAD is like OpenSCAD but with a good language. Added code to make the disks (will generate STLs for printing or DXF for cutting, and I can make it do SVG as well if needed). I probably want to move the STGC track to reflective rather than trasmissive. We need the transmissive (slots) for the analog reading because it increases the bandwidth. But the STGC reading is just on / off, not analog, so reflective should work, and avoids the need to have a light source on one side and a sensor on the other.

https://github.com/JamesNewton/HybridDiskEncoder/blob/master/stgc_wheel.jscad