Leg Mounted Beer Bottles for Underwater Propulsion

Sitting on the beach, finishing off a beer one day, [Rulof] realized that if he put a motor in the beer bottle with a propeller at the bottle’s mouth, he could attach the result to his leg and use it to propel himself through the water. Even without the added bonus of the beautiful Mediterranean waters through which he propels himself, this is one hack we all wish we’d thought of.

These particular beer bottles were aluminum, making cutting them open to put the motor inside easy to do using his angle grinder. And [Rulof] made good use of that grinder because not only did he use it to round out parts of the motor mounting bracket and to cut a piston housing, he also used the grinder to cut up some old sneakers on which he mounted the bottles.

You might wonder where the pistons come into play. He didn’t actually use the whole pistons but just a part of their housing and the shaft that extends out of them. That’s because where the shaft emerges from the housing has a water tight seal. And as you can see from the video below, the seal works well in the shallow waters in which he swims.

The batteries for powering the motor go in a separate watertight PVC cylinder mounted on his upper body, with watertight seals for the wiring going from the battery cylinder to the bottled motors. But how to make a watertight on-off switch? For that [Rulof] put a reed switch inside the battery housing. The reed switch energizes a relay, and the relay electrically connects the motor to the batteries. He made sure to mount the reed switch near the PVC cylinder’s wall. To close the reed switch he brings a magnet outside the cylinder to near where the reed switch is inside the cylinder. To open the reed switch again he moves the magnet away. So the reed switch remains inside the watertight cylinder while the switch is opened and closed using a magnet field from the magnet outside the cylinder.

[Rulof] isn’t the only electric fish in the sea. There’s also this fin propelled robofish that can communicate with others of its kind using Sonar. And then there’s jet propulsion, sucking water in one intake and expelling it out the other as does this ROV.

35 thoughts on “Leg Mounted Beer Bottles for Underwater Propulsion

  1. Even easier: leave the bottles capped with the beer in them, shake well, strap them on as shown, and poke a little hole in each cap after getting in the water. Use the money saved by not buying all that electrical stuff to buy more beer to drink (and to recharge the rocket motors).

  2. I don’t get why the beer bottle/cans were used at all. I think the intention was to keep the motors dry (which you’d probably want in salt water) but I seriously doubt they do that at all. They probably do a good job of making it difficult to fix the vinyl tubing coupler when it breaks. And it will break. Those wire “pins” will make certain of that as they cut into the tubing already weakened by the hole they pass through.

    A more bulletproof approach would be to use small, submersible aquarium pumps (aka power heads) intended for salt water. Those have totally sealed stators and rotors and I’d imagine comparable thrust.

  3. If thrust could somehow be increased, this could result in Iron Man – like underwater manoeuvrability. The on-off switch would not be enough anymore, though – I’m afraid one would turn into a twin-headed blender trying not to blend itself! Let’s fire off a tip towards Colin Furze and buy some popcorn.

  4. I have two questions. I think this is a great hack, but…. for the size of that motors? I think rc motors can get a lot more revs 18k revs or more, and that only do 4k… and are smaller a lot let smaller! The blades are really small i think he could use ones with double size would improve a lot its power.

    Why cutting the sneakers?
    And why not bigger blades/other more efficiently motors?

    1. It’s a hack.
      Open beer. Look at water. Get crazy idea.
      Open toolbox. Grab parts that won’t be missed. Cut sneakers.
      Cut bottles. Put together. Jump into water.
      Smile because it worked!
      Buy new sneakers. ;)
      .
      Try it again with better parts from boat store and RC shop.
      Or…
      Do something else that is fun.
      I personally think there is MacGyver envy here! :O

    2. I’m pretty sure that 18K rpm would destroy the propeller. And if it doesn’t, you’d get cavitation at those speeds.
      If you want more propulsion you’ll need bigger fan, and more torque.

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