Gonna need people's help here, I'm brand new to 3d modeling and have no printer to work with, so it's all trial and error. The theory goes that if you print either of these two items, place them in a bottle of water, top it off and close the cap, then squeeze it will act as a proper Cartesian Diver (or Devil)

http://en.wikipedia.org/wiki/Cartesian_diver

I don't have the facilities yet to test this design, I'm hoping that the way i modeled it it should spin when you squeeze and release a couple times... if not... well back to the drawing board..

It was modeled in wings and if anyone wants a copy of the .wings file (or whatever wings3d can export to) just ask!

Print Bobbie 1 or 2, (remember to scale so it can fit inside a plastic (read: squeezable) water bottle,

Fill the bottle almost all the way, put Bobbie in, top it off, cap it and squeeze. the air bubble inside the Bobbie should be compressed and therefore sink to the bottom, then when you let go it will rise back to the top..

please report back on if this works or not, (and if it spins at all) Bobbie 1 should work, but if it's too buoyant then print Bobbie 2.. thanks!