Have you ever considered building some kind of underwater vehicle? It’s rather ambitious but [Dane] of Transistor-Man has designed and built a working submersible 3-phase electric thruster — and he’s released the plans online for all to share!
He decided to make this for his 3D printed canoe (another awesome project) which is possible due to his massive SCARA robot 3D printer. The thruster makes use of readily available off the shelf components, but with 3D printed cones for decreased water resistance and other manufactured parts. The housing is water-jet cut, and the poly-carbonate tube had grooves for seals made using a lathe. The amount of detail in his build logs is incredible — he’s fully modeled all parts in what looks like SolidWorks and uploaded detailed images and designs of all the parts.
The trickiest part of the build was making it water-tight. His first test was to submerge it in a water bath for 8 minutes, and once that was proven, he filled the inside with 5W-20 oil to make sure it wouldn’t leak the other way as well. One of his project goals is for this thruster to work 1 meter underwater without losing more than 10ml of the coolant (oil) per hour.