This is basically the same thing as the one by RichMac without spacers and resized. I ported the files over to AlibreCAD, and resized it all for a 3mm shaft. I also made the rotors use hex insets, so 3mm locknuts provide the torque. This may not provide useful amounts of power, but it sure is effective in just making it spin. No spacers needed, just three or four 623 bearings two or four 3mm locknuts, and at least 35mm of 3mm socket cap screw - but that short and nothing sticks out. 50mm+ recommended. http://www.youtube.com/watch?v=K5l5G1aihk I had a smaller vacuum too so now it fits on a 28mm wide hose.I'm still working out if this provides usable torque or if the spacer design of the original is needed. Adding a way to get power out is needed to test that... Also still working on the screw threads in AlibreCAD after all my re-sizing. Print 2x rotors, 1x stator, 1 each housing. Press a 623 bearing in each housing and the center stator. Press locknuts into both rotors. Push the axle through the front stator housing. Thread a rotor as far down as it will go without scraping when rotated. Slide center stator in place (wide side away from the stator housing), then screw the next rotor on similarly to the first. Slide/screw the top housing in place and test that it can freely rotate. Spin by hand and you should feel some air come out. Attach to vacuum and annoy any cats that happen to be around.