Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4922371.

An experiment in designing prints for moving parts. This torpedo has enough room to thread several rubber bands through the back, which then allow the part to be wound up and released. Can fly up to 6 feet before slowing down and drifting.

• Thread 1-4 rubber bands (depending on size) through the lower half so the ends protrude from its top.
• Design and add a washer / glossy "bushing" to the top of the lower half and thread the ends of the rubber bands through it.
• Using the included pin, lock the ends of the bands onto the upper half of the torpedo to finish assembly
  • (NOTE: you'll need to adjust the model to fit some sort of high-gloss washer between the halves to allow them to spin freely against each other).
• Once assembled, twist the lower fins in the direction that their ends point towards. Place underwater and release!

Original .Blend file is included to allow you to modify the lower half to fit your own style of friction-reducing washer. I just used a glossy metal cap from an old lamp stand.

Future improvements:

• Locking/Firing mechanism. I plan to add some way for the upper and lower halves to key into each other once wound up to act as a trigger mechanism.