At this year's International Robot Exhibition, Masahiko Yamaguchi demonstrated a smallish robot--maybe a foot high or so--that is able to ride a fixed-gear bike, like a 2011 version of the opening scene from The Muppet Movie (and there's a Muppet movie coming out this year, too! Sorry sorry. Back to robots.) What's especially impressive is that the robot is capable of biking just like a human--it moves and brakes solely through the strength of its own adorable little body.
According to DigInfo, this is essentially an off-the-shelf robot, outfitted with a Tamagawa Seiki-made gyroscope to help the little guy keep his balance. A control board in his backpack processes the signals from the remote control, calculating how sharply the 'bot can turn the handlebars while maintaining its balance.
It uses a fixed-gear bike not out of trendiness but for a more simple reason: the robot would have a tough time managing a freewheel, which allows the back wheel to spin even if the robot stops pedaling. Also, a fixed-gear allows the robot to brake simply by slowing or applying reverse pressure to the pedals. He stops the same way you and I do: by taking his feet off the pedals and balancing on his toes. Perhaps the world's most failsafe electric brakes are a bit too complex for this minimalist robot cyclist.