Toothbrush Torpedo STEM competition

This time of year, our team is always looking for a new, exciting way to engage students. We do the aluminum foil penny-boats, we do the spaghetti-marshmallow towers, but this year I came up with a new engineering competition…

Toothbrush torpedo races.

I’ve looked at electric toothbrushes for years wondering if we could 3D print some parts and make a competition vehicle. So I finally designed three parts…a shaft, a bearing with fins and a prop and got us started.

We cut off the brush-end and pull the body apart to put in the shaft, then after a bit of fiddling to get everything turning nicely, put the fins and the prop on and voila, a motorized torpedo.
I thought the competition would be for people to design better props and fins, but turns out it’s so heavy it sits in the water on the bottom, without enough thrust to move. So the competitive part was adding enough floatation to keep it off the bottom but keep the prop in the water without too much drag.

I coupled this with ten minutes of fluid dynamics lecture, talking about stability, center of pressure, weather-vaning, propeller design, wetted area.

Anyway, competition was fierce and fun.

I’ve put CAD files and some pretty careful directions on GrabCAD.



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