My proposed final project is a macro-scale artificial flagellum.
Above is a rendering of an actual flagellum, which is basically just a molecular string that gets spun really fast. I want to make a flagellum that can power something larger, like a small boat. Unfortunately, spinning a cable-like structure won't work. But we can make a flexible, long fin that behaves similarly when spun.
When the fin is stationary, it should have a particular curve along its length, but no twist. When in motion, it should become a spiral, essentially corkscrewing through the water. It was really hard to model this shape correctly. Here's one of my failures.
My idea is to create a small pod that contains a motor and affix one (or two) of these fins to it.
This pod could then be affixed to some sort of watercraft. Below I've modeled it attached to the bottom of a long canoe. It would be hooked up to a battery and some sort of controller that could vary the rotational speed.
This seemed like kind of a neat idea, and it would certainly be fun to ride around in this canoe. But it seems a little unambitiious. So I'm also considering adding fins to the pod, and turning it into an autonomous water vehicle. The fins could stabilize the counter-rotation of the spinning flagellum, and allow the contraption to zip around like a new kind of fish.