Lego-Powered Sub Built In A Water Jug

Submarines are universally considered cool, but bring several challenges to the RC modeller that aren’t there with land and air builds. Water ingress can ruin your project, and there’s always the possibility of it sinking to the bottom, never to return. That didn’t phase [Brick Experiment Channel], however, and thus a Lego sub was born. (Video embedded below the break.)

The sub uses a water jug as a hull. The video steps through the process of sealing the hull itself, before dealing with sealing the rotating propeller shafts. A large syringe is used as a ballast tank, with Lego motors used to actuate the tank and provide propulsion and steering. An existing RC submarine is cannabilized for parts, providing the necessary radio control hardware.

In testing, the sub performs admirably, with a few final tweaks necessary to improve the performance of the propellers. It’s not winning any races anytime soon, but it’s a functional underwater explorer that we’d love to take down the lake ourselves sometime.

We’ve seen Lego subs built before, even including missiles.

[Thanks to RodrigoTorVal for the tip!]

16 thoughts on “Lego-Powered Sub Built In A Water Jug

  1. interesting project, although I have mixed feeling about a sub being gutted for it’s part to control the jug.
    It seems to work fine and the syringe ballast tank is a great idea, cool project!
    The handle of the jug seems to be very practical.

    1. Yeah, I get it from a cost standpoint, but I would have liked to see it done with some more mature RC gear.

      Also somewhat surprised to see that it’s so water tight with just the friction and plumbers tape.

  2. Very clever build. In one of my recent projects, I used hot melt to seal water to wood and tubing for a watering manifold and it is not as good as epoxy. It works well enough to let it be for now, but if I ever re-do it, I will use 24 hour epoxy to seal everything up. The other thing, in the holes for the props, you may also want to try gluing something like pill bottles on the inside and filling them with thick grease, and running the shaft through that along with your o ring solution. I really enjoyed the build. How much range do you get out of that little subs remote?

  3. Very nice project ! Congratulations ! I would suggest using a magnetic drive (as in the sealless water pumps used in washing machines) to drive de propeller; in that way you can be almost 100 % sure the hull will be leakproof.

    Best regards,

    A/P Daniel F. Larrosa
    Montevideo – Uruguay

  4. At the surface you should be buoyant with your syringe mostly filled with water.
    As you go down you will need to displace the water with air in the syringe to get buoyancy at depth. You may have noticed that you could make the sub go down but not back up (without string).

    Ask any scuba diver.

    1. The water displacement of the container remains the same volume as before assuming the container doesn’t deform from the water pressure. The total weight of the sub is reduced by the amount of water removed from the syringe.
      A syringe actually has 2 compartments – one side you didn’t consider is the open end side of the piston filled with air from the container.
      I worry more about the container not designed to handle any great pressure and may rupture before the water is deep enough to cause a retrieval problem.

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