The models were created in Moray for Windows ( http://www.stmuc.com/moray/medown.html ). The attached zipfile contains the plugin I wrote to export primitives from Moray directly to OpenSCAD (see readme in zipfile for instructions).
This impeller housing was designed to work with a 35.5 mm diameter motor having a 4 mm diameter shaft, and mounting holes about 25.4 mm apart (M3). It was built around a scaled version of the impeller here: http://www.thingiverse.com/thing:34563/#comments.
The motor I used came out of a cheap 18 V electric drill.
.mdl files were created in Moray For Windows ( http://www.stmuc.com/moray/medown.html ). The zipfile contains the export plugin to OpenSCAD which was used to compile STL files from the Moray scenegraph.
Note - Moray exports primitives, not meshes. Excellent for doing CSG :D