The Hunt for Mini October




Introduction: The Hunt for Mini October

The title of this instructable is freely inspired by the 1990 movie "The Hunt for Red October".The film is based on Tom Clancy's 1984 bestselling novel of the same name.

The story is set during the late Cold War era and involves a rogue Soviet naval captain who wishes to defect to the United States with his officers and the Soviet Navy's newest and most advanced nuclear missile submarine.

It was built with a revolutionary stealth propulsion system called a "caterpillar drive", which is described as a pump-jet system in the book. In the film however, it is shown as being a magnetohydrodynamic drive.

A magnetohydrodynamic drive or MHD propulsion is a method for propelling vessels using only electric and magnetic fields with no moving parts: it exploits the Lorentz's Force. The voltage applied to the electrodes produces an electric current (due to ions) between them. The ions are moving in a magnetic field B and because of this they are pushed in the direction shown by F generating a thrust in the opposite direction. The net thrust is indeed generated by the balance between positive and negative ions moving in opposite directions: when you pass an electric current through a solution, ions (charged particles) migrate towards the electrode of the opposite charge. This will lead to an (at least here) unwanted side effect: the electrolysis (see note).

The aim of this instructable is to create the most advanced, stealth and terrific pocket MHD drive ever.


In a salt solution (NaCl) the dominant species of ions are sodium (Na+) and chloride (Cl-), because only a tiny amount of water (H2O) is ionised (to H+ and OH-) at pH 7, and that's why pure water is very difficult to electrolyse.

The electrolysis of salt water can proceed in several different ways, depending on the nature of the electrodes, and the concentration of the sodium chloride.

With inert electrodes (silver, platinum, glassy carbon), you will produce hydrogen gas at the cathode, and either chlorine gas (concentrated NaCl) or oxygen gas (dilute NaCl) at the anode. But copper electrodes are far from inert. Instead of producing either of these gases at the anode, the most likely anode reaction is erosion (gradual dissolving) of the copper anode (going into solution as Cu2+ or CuCl2-). Another chemicals is obtained during the process, sodium hydroxide (NaOH). On top of this chlorine and sodium hydroxide react when they come into contact with each other. So... the electrochemical part is pretty complicated, if you want to know more i suggest you to google for papers about "seawater electrolysys" with "copper electrodes"...

Step 1: Materials Needed

To build this MHD drive you need:

  • the ready-to-print STL files
  • two magnets 40x20x5mm N52 grade (Part number F40205-N52-1)
  • 3mm diameter x 0.45mm thickness copper tube
  • tube cutter
  • 9V battery and battery holder
  • cyanoacrylate glue
  • soldering iron
  • wires

I got all my hardware on Amazon, but i think you could easily find everything somewhere else as well...

Step 2: Assembly the MHD Drive

To assembly the device follow these steps:

  • download the zip containing the STL files and 3d print the needed components (I had mine 3d printed from a friend because I don't have a 3d printer ehm ehm... ^^)
  • cut the copper tubes to a lenght of 40 mm
  • solder the power wires to the copper tubes, keeping the junctions as small and flat as possible. I added two male pin terminal, but it's not mandatory. The 3d printed frame has some recess built into it to accommodate the junctions anyway
  • carefully insert the tubes and the magnets in the main frame. Be very careful with the magnets: they can cause cuts and blood blisters if handled incorrectly. Read the warning sheet BEFORE handling them!
  • replace the connectors of the battery with female pins if you added the male pin terminals as well
  • glue the noses in place using the cyanoacrilate glue
  • glue the fins in place using the cyanoacrilate glue

Ready to test!

Step 3: Test the MHD Drive

To test the device and checking if it is indeed emitting a jet of water you will need:

  • a transparent container filled with salt water (2 tablespoon of salt per liter of tap water will do the job)
  • a syringe and some cake decoration color

Connect the battery pack to the device, check that the switch is OFF. Sink the device in the bowl, wait for the surface to settle and switch it ON. Pick some coloring agent with the syringe and slowly inject it right in front of the MHD drive opening... you should notice that it will get sucked into the device and expelled on the other side. If it doesn't happen... just try the other opening :)

I've done it! You just created your first magnetohydrodimamic propulsion system!

Step 4: Safety Notes

As I mentioned before, working with strong magnets is fun but you must always be aware of the risks as well. i suggest to read all the safety advice here if you decide to replicate this experiment, and to do this even BEFORE you order your brand new magnets.

The device require also to use electrical power AND salt water. A potentially dangerous combination. While you are pretty safe using a 9V battery, you could possibly think about increasing the voltage to increase the performances of the MHD drive... well, don't do this unless you are expert in dealing with high voltages and electrocution risks.

It is the responsibility of the user of this circuit to be familiar with all applicable safety practices regarding its construction, testing, and use.
Wear safety glasses and use all appropriate safety equipment when working with tools and materials. Always follow safe shop practices and obey safety rules. This device is recommended for users familiar with electronic theory and construction practices.

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    4 Discussions


    3 years ago

    Cool engine! Efficiency is really low (probably a few % achievable with practically available magnets and reasonable current - quite good research is here: ) - but still very interesting


    Reply 3 years ago

    Thank you the_3d6! :) And thanks for the link, it's a very in deep analysis.


    3 years ago

    That's neat! :)


    Reply 3 years ago

    Thank you Swansong! Just add water they used to say... (?) :)