https://makezine.com/article/digital-fabrication/3d-printing-workshop/the-theta-3d-printer-4-extruders-on-a-polar-coordinate-system/
The Theta 3D Printer: 4 Extruders On A Polar Coordinate System - Make:
Nov 11, 2014 - Traditional 3D printers, as well as most CNC routers, laser cutters, and most machine tools where the programmer doesn't want to go crazy trying to
polar coordinate system