TeTWalker, the shape-shifting tetrahedral walker under development by NASA, is back in the news (see the previous story TETWalker: Shape-Shifting Robot Swarm). A next-generation prototype successfully navigated the terrain around Meteor Crater in Arizona.
The simplest version of the device (the one that conquered Meteor Crater) is a single tetrahedron walker. For those who do not recall, a tetrahedron is a geometric solid with four plane triangular faces. The robot really is a shape-shifter; its struts can telescope and retract, thereby pushing the nodes out or pulling them back in. Various combinations of this trick lead to a unique way of walking. One of the project designers, Professor Pamela Clark, refers to it as a "drunken sailor walk" because it is so irregular.
The advantage of this sort of walk is that it can be the ideal way for a robot to negotiate highly irregular terrain, like the surface of Mars. A 12 tetrahedron version is currently under development; as the number of tetrahedrons increases, the motion of the robot really starts to flow nicely in an amoeba-like fashion - see the very cool video below). It can even scale chimney-like structures like a human climber.