A Möbius Gear

Wait -- a toothed gear that has only one side? Is that even possible? Aaron Hoover, a robotics student at Berkeley, says that it is:

[...] I convinced myself that this mechanism is indeed possible and that with right tools, a functional prototype could be built. (The entire mechanism essentially boils down to an oddly configured set of planetary gears. One can think of the black portion in the image as the ring with a fixed zero input velocity. A single blue gear is a planet, and the white strip is the sun. Output can be taken either from the sun or the planets (with no regard for practicality!). In practice, however, it’s easiest to actuate the Möbius strip (the white portion). So, using a combination of the Scene Language for Dynamic Environments (SLIDE), developed here at Berkeley, Tcl, Python, and Solidworks, I was able to create models of the constituent components. The base was fabricated on a Stratasys fused deposition (FDM) machine and took approximately 86 hrs. to finish. The “spur” gears were molded in silicone rubber using a two-part mold printed on a 3D Systems wax deposition machine (ThermoJet). And the central Möbius strip was also molded using molds printed on the 3DS machine. The Möbius strip was molded as a single linear strip then twisted and the ends were rejoined in a “guiding” mold and additional rubber was poured into that mold to bond the two ends together and form a single continuous ring. The end result is a functional prototype, but rotating the middle ring without having the blue gears pop out is a little tricky.

http://robotics.eecs.berkeley.edu/~ahoover/Moebius.html via Make