Eulachon Thruster V2


I've been tweaking my thruster design, and you can click here to download the latest thruster files (Solidworks). The main improvements are that the thruster has been made a bit more streamlined, the part count has been reduced, and it's much easier to fill the body with oil now. That's not to say that there isn't room for further improvements, but I'm much happier with this updated version.

In other exciting news, a Techshop just opened up about 5 blocks from my house, so it looks like I'm going to have access to some of those fun tools that will allow me to make the more complicated parts like the prop shrouds.

Happy building,


P.S. A note on using these files. With the last thruster design, there were a lot of proposals for different uses of this design. I'm going to attempt to preempt some questions by posting these files under the same creative commons license as OpenROV:

Creative Commons License
Eulachon Thruster by Ben McCandless is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

If you have further questions, please feel free to contact me.


Update: I've added a STEP file of the assembly to the files. If you don't have SolidWorks, you should be able to import that into most CAD programs.


Nice work! I hope you could fabricate it quickly and see how it performs.



The parts were printed last night on my Uprint. The parts are currently in the tub to remove support material. I will post pictures as soon as they are finished.


That's great! I can't wait to see them!



That's fantastic!


Wow I like these I could use those on my build :) because I am using a different Hull than the Open ROV. Did you want my Shipping address and Visa Number :)

What is the max dia of Motor that will fit in this? My motors are 3mm Dia

I also am using a 5mm shaft which should not be a problem.



I think that at 35 mm diameter, your motors are a bit too wide to fit into the polycarbonate tubing that I used for this version of the thruster. You could certainly modify the design to fit it, but there's a few things that might make that a tricky process. The motor you've picked out has a cross section that's 50 percent larger than this one. which means that you'll have to adjust the flow of the water around that greater bulk, and resize most of the components. (On the plus side, you'll probably get much better torque out of the magnetic coupling, to match the much more powerful motor.) It's certainly do-able though.



The link to the files seams to be broken


I've reset the sharing and link settings - try again?


How is this going? Are things still in motion?

Looks super cool. :)


Actually, it went pretty well - though there is some room for improvement. I was able to build and test the final unit, and I've been meaning to write a post about the details. Expect another post in the next week or so.



Hi Ben,

Certainly a very interesting read!

I’ve downloaded the files in view of having them printed, before I do that are there any lessons learned that I should be aware of?

Any chance of a project update?

Best regards,





  • Smooth motor control is a must, otherwise it is difficult to control the sub.
  • The magnetic couplings are not strong enough and need to be expanded. V3 will cover this. If you are proceeding on your own, I'd suggest 2x the length of the magnets in the motor-mag-mount, and 4x for the prop-mag-mount
  • Getting the magnets into the prop-mag-mount was a bit tricky. V3 will provide for better clearance in the corners.
  • Getting air bubbles out of the oil filled thruster is tricky due to the concave down geometry of the motor-mag-mount. V3 will add air holes to help with this.
  • Sucessfully sealing the thrusters so that oil does not leak out is tricky. It turns out that oil leaks through the wires (between the strands and insulation) Future versions should use solid core wire.
  • Wiring the thrusters to the rest of the sub is also a wee bit tricky. I'll be using waterproof connectors in the next version so that everything is plug-and-play. (Something like this.)

I have a bunch of plans for updating the sub, but I have other projects that are higher priority and I'm a bit limited for time, so it might be a while. :-( As I mentioned above, I still need to write the post describing the final construction and launch of the Eulachon. I'm still waiting on some of the pictures from the launch from a friend - hopefully soon!



Hi Ben,

I hope you’re keeping well?

How has the design of V3 of the thrusters progressed? Are these available for release?

All the best,




Sorry for the long delay without a post - it's been a busy year. The latest news is that the V3 design is ready for production - or was until last week, when I found out that the magnets I was planning on using were out of production. That's probably going to slow me down quite a bit, as I have to either find OTS magnets that suit my purposes, or convince someone to make the perfect magnets.

On the other hand, I have a whole bunch of improvements in the works:

  1. Better sealing - no more wicking of oil through the wires
  2. Quick exchange - the motor pods will be plug-and-play, no need for soldering or difficult connections. Just unplug the motor pod and put a new one on.
  3. Higher stall torque - much more powerful magnetic coupling (assuming I can get the magnet situation worked out)
  4. Fewer rapid prototyped parts - if you have access to a lathe and a Makerbot Replicator 2, you should be able to make a set of these.

There are a couple of trade-offs, though.

  • The new motor pods are going to be a bit longer (off the top of my head, I think it's roughly 20 mm) than V2.
  • In the interest of reliability and ease of use, I've added a couple of more expensive components.

I actually talk about these a bit in the most recent dev call.

Hope this helps!



Hi Ben,

Thanks for the update, sounds excellent!

If possible, could I get a copy of the designs? I’ll get them put into production next year uk

All the best,