Three-Phase Submersible Thruster is Open Source and Awesome


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.

It’s a seriously impressive project — just take a look at the following videos!

25 thoughts on “Three-Phase Submersible Thruster is Open Source and Awesome

  1. While it is indeed a three phase motor, they usually aren’t ever called as such. It’s a BLDC motor, which all have at least three phases, but usually just get called “BLDC”. I am disappointed to see that this does not use any standardized motor frame (size), so while it is from “Part of a special order from the Shady Melon Motor Co. Ltd”, good luck finding other motors to substitute or anything of that sort in the future (although I’d like to see it handle 7kW!)

  2. surprised Im the first to say something….but arent there better choices of coolant? I get that he designed it not to leak much but leaking 10ml/hr of a ecofriendly biodegradable oil vs motor oil would be better…wouldnt it?

    1. Good question. Because i opted for a polycarb outer casing, i couldn’t use wd-40 (which would have been awesome), as it dissolves polycarb. Most of the losses are through the shaft seal under load, The benefit of mineral oil is its low viscosity, but that also equates to ‘easier to slip through the shaft seal’

    1. Hi! Yeah it is a bit noisy, the propeller needs a bit of balancing. Normally, dc trolling motors are 300-600w, this is ~5-10x the power. I think upgrading to a sinusoidal controller and stiffening up the rear cowling might reduce vibrations.

        1. R/C motors run under square wave commutation (“brushless dc”) are extremely loud. I wouldn’t be surprised if this were the dominant source of noise for this one, given how much of it is motors.

  3. ” One of his project goals is for this thruster to work 1 meter underwater without losing more than 10ml of the coolant (oil (5w20)) per hour.”

    One drop of oil can contaminate One milion drops of water………

    Perhaps tests in some tank would be more wise than test on open water when putting 10ml of oil per hour into it….

    just saying…

    besides that, pretty cool stuff…

    1. Yep!
      Thats the exact reason I’m using mineral oil, its non-toxic and still meets the lubrication requirements, so if it does leak, its not destroying the remaining aquatic life in the Charles river.

  4. Why use anything other than water? It is purely for the bearings? There need not be any exposed connections in a 3-phase motor, so conductivity of the fluid doesn’t matter. I get that grit in the system would be bad, which may be why the housing exists at all. Otherwise, just drill holes in the housing and let it fill with water. But for the sake of the bearings to keep sand out, a slightly positive pressure is probably good.

    Assuming this thruster is for a surface vessel, positive pressure is super easy… just run a tube up along the control wires to the boat. As long as the level of fluid (say, filtered water) in the tube is above the surface of the surrounding water, there’s no doubt there’s a positive pressure down in the motor housing.

    If this is for a submersible, one could use a spring-loaded syringe with two flapper valves. Pull the syringe while it’s under water before the mission to fill it up, and as long as the leakage doesn’t exceed the volume of the syringe before the mission ends, no worries. This works at any depth.

  5. I’d suggest using Dextron VI over motor oil. It’s much lower viscosity, so less losses, and it has some corrosion inhibitors. Some production 3-phase motors (Remy HVH series, used in the Chevy Volt among others) use it for internal cooling so it’s a good bet for your application.

  6. For the leak check you can either create a test cap with a quick connect in it ( we used these qd’s with a whole tapped deep enough to make a seal using an o-ring (2-012 should get you close) and use the hand pump used for testing brakes on your car. You bring the pressure up to about 10psi and submerge the housing and see if you see any bubbles. Additionally you can put it on a vacuum with the same hand pump and let it sit for a little while to see if you lose the vacuum. The other option would be to permanently add the qd to the design. Then you can hook a vacuum pump to a modified paint pot and pull the air out of the housing with the vacuum and allow the housing to back fill with oil. This will make sure that if the motor stator is not sealed then the air bubbles in the winding’s are as small as possible and giving you a more static enclosure. If the housing is oil filled and not a 1 atm enclosure then putting a diaphragm in the end cap to make the seal and opening the end cap to ambient pressure will create positive pressure in the housing if you overfill the housing thus buying you some time if there is a small leak (smaller than 10ml/hr, that is ALOT of oil leaking out). I didn’t see assemblies of the shaft seal hopefully that is the only place that is leaking oil. It would also be beneficial to print several different props and play with the pitch and shape of the blades to find the greatest output.

    It should be a fun canoe just the same.

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