Physicists have solved a key problem of robotic locomotion by revising the usual rules of interaction between simple component parts. In cycling through a sequence of shapes, an odd wheel propels itself up steep and bumpy terrain. In a physics lab in Amsterdam, there’s a wheel that can spontaneously roll uphill by wiggling. This “odd wheel” looks simple: just six small motors linked together by plastic arms and rubber bands to form a ring about 6 inches in diameter. When the motors are powered on, it starts writhing, executing complicated squashing and stretching motions and occasionally flinging itself into the...