I made this adding a 2212 motor and 3a esc as that's what I had laying around, used the recommended rubber bearing with 3mm stainless shaft, used silicone to seal the bearing in place, and then plenty of grease when putting the shaft in. I don't know how others attached the impeller but what I did was drill a little hole in the shaft and glued in a small pin through the impeller. Boat works well for me. Kids will be sure to enjoy this too.
Printed on one of the cheapest printers I could buy too.