A Japanese roboticist that goes by the handle Dr. Guero, famous for programming his hobby robot to ride a miniature bicycle and walk on stilts, has managed to get his robot to balance on a tightrope. His Primer-V4 robot is based on the Kondo KHR-3HV hobby kit (which can be purchased for around US$1,800), but features a few modifications that give it the ability to inch its way along a steel wire just over an eighth of an inch (4 mm) thick.
The following video shows Dr. Guero's robot as it slides its way along the wire, making minute adjustments to its balance by waving its arms. On his website, Dr. Guero explains that the robot's arms move in different directions based on signals from its inclination sensor. He had to modify the feet by adding grooves to help catch the wire – which seems like a fair modification given that human performers will use their toes to do the same thing. He also replaced the standard arms with ones that have fewer servos and parts to provide better balance.
Dr. Guero (aka Masahiko Yamaguchi) has worked at some prestigious labs, including Japan's National Institute of Advanced Industrial Science and Technology, Boston Dynamics, and Osaka University. His nickname, chosen by his wife, comes from the long-running comic and animated television show Dragon Ball Z, whose Dr. Gero is an evil scientist behind the Red Ribbon Androids. You can watch the tightrope trick below, and check out his earlier projects on his website.
Source: Dr. Guero's website (Japanese)