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by Patrick_B Jul 19, 2015
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What is the function to the larger body section?

It was originally designed to house a spring-loaded gear assembly instead of a rubber band, but I could never get it to work.

It would be pretty easy to redesign that section to look nicer, but I haven't taken the time to go back and update this model.

Ah I think I understand. I was trying to print this project because it looks neat and I want to see it in person. That one part doesn't want to print on my machine and it sounds like its not a needed part if I follow. Thank you.

Well, it's still required - I just meant that it should really be redesigned and made smaller. The front-end of the large section holds the hook-part that the rubber band attaches to.

Ah I get you. Its a cool project, Thanks for sharing it. Hopefully I'll get a chance to build and play with it some. I'd like to see about trying a counter rotating prop in something like this.

why not add some wings to the body to stabilize it

Yep, more and bigger wings/fins would help resist the twisting, and get more thrust out of the propeller. There are definitely a lot of improvements that can be made to this project, I just haven't found the time to come back and tweak it.

Great project! Love the execution I've made a few before as a kid and later when I worked for a toy company. Yours looks very Pro! I have a couple of suggestions to improve performance.
I found that mid wings keep it from counter rotating, you can also bend the trailing edges of the fins to induce a roll in the opposite direction (simpler).
I also noticed the curvature of the propeller is backwards, the high point of the curve of the blades cross section should point forward and the gentle edge of the blade is the leading edge and the more pointed edge the trailing edge. Very easy thing to miss, I've done it before on my RC planes and wondered why they were so slow :) By flipping it around you should see a gain of 20-30% in thrust. You can also make the blades thinner for better efficiency. There are several ROV blades on thingiverse that you can see what I'm talking about.
Again, very impressive work! hope to print one out for my nephew.

Hey Isobot, thanks for the warm comment!

I vaguely remember mirroring the propeller so that the torque was in the direction to tighten the shaft-screws, instead of undoing them. I think that's why the blades are curved wrong - I should have left the blades alone and just flipped the cone to the other side to maintain the proper blade curvature. Rookie mistake, great catch!

Yeah, I think putting the fins in the middle, and adding another propeller to the back would be a better design. I should really make some updates to this project - it needs a few tweaks to make that a possibility. I also thought about making a special double-shaft part that lets you add a second torpedo shaft to the design, so you could have side-by-side torpedos attached in the middle like an H. Then you could have two front-facing propellers with opposing spin directions so they each offset the other's torque.

We'll see if I ever find the time to revisit this project, but I think it definitely deserves an upgrade. =)

You can reduce the rolling moment of the rear section if you make the fins larger and add a second pair on the mid housing. This will also increase the range, since the prop will turn more times before the rubber band goes slack. Real nice work.

This is a fun design. @Makerbot This would probably make for a good featured build. Thoughtful and inspiring.

This is exactly what my submarine model is lacking :D thank you! Although now I have to design launch tubes...;)

Cool! I'm glad you like it. You might need a pretty big submarine to launch these things out of - they're pretty big. I uploaded some photos that give a better sense of scale.

Still, no reason it can't be scaled down and modified to work as a smaller torpedo.

Best of luck with the submarine!
-- Patrick