Even Joke Torpedoes Are Pretty Hard To Get Right

It’s rare that makers get involved in out-and-out munition production. It’s dangerous, and usually frowned upon by local authorities. That said, it can be fun to experiment around, and [Ivan] does just that, attempting to launch a 3D-printed torpedo from a kayak. The build may have been done as a marketing exercise, but it raises some interesting questions about naval engineering.

The first revision consists of a 3D-printed hull, containing a rubber-band powered propeller. A soda bottle filled with compressed air is then used as a warhead, fitted with a contact fuse to release its charge on impact. Unfortunately, initial tests were underwhelming, with the rubber band mechanism failing to provide any real forward propulsion.

A trip back to the drawing board was due, and the design was revived with a brushless motor powerplant instead. This allowed the torpedo to trawl, albeit slowly, through the water. It also proved that the compressed air “warhead” could successfully discharge, albeit with less of a bang, more of a whimper.

The build, while undertaken for the sake of fun, does highlight some of the engineering challenges inherent in building a working torpedo. There were issues with buoyancy, as well as providing the torpedo with enough power to move quickly in the water. On top of this, the matter of guidance is also an important one. We’d love to know how the Hackaday commentariat would go about solving these issues when undertaking their own build – let us know down below. We’ve seen others tackle similar builds before, too. Video after the break.

7 thoughts on “Even Joke Torpedoes Are Pretty Hard To Get Right

  1. Good build, but underpowered. Soda bottles can be pressurized “safely” to 10 bar, as many water rocket sources can confirm. As a fake warhead or as engine power, its severely unused.
    Directional control was also missing (thus the torpedo goes back to the shooter), an arduino, servos and a compass would solve this.
    In any project there is a balance between the quality of the build and the features. This project lacks features.

    1. Think the goal was to do this as cheaply as possible. ‘Features’ add complexity and expense. I’m no expert on war and weapons, but I’m pretty sure, originally, torpedoes were launch, and mostly traveled in a straight line to the target, exploded on impact.

      I like the compressed gas in a PET bottle though, and could probably get good range, and speed. A simple valve would adjust your preference and performance. Instead of a separate bottle for a warhead, just release the remaining gas from the one(s) used for propulsion. Doesn’t look like it would be a problem fitting 2-3 bottles in there. Maybe design a more streamline body, make it cut through the water efficiently.

  2. A friend of mine in the 1980’s made a duck torpedo that used two tiny water-rated microphones pointed forwards and two backwards. The rear-facing ones sampled the sound of the prop and subtracted that from the front-facing ones, which were hooked up to differentially signal the sound of ducks paddling their feet in the water. It was not fast (he didn’t want to mow ducks down) but it did home in on the nearest duck. It was entirely analog, using op amps for the differential signaling and the inversion of the signal. He had a lot of trouble with op amps of the time not being fast enough, and played a bit with moving the rear-facing ones way back near the end to help offset the signal delay.

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