Lucerne Valley, CaliforniaThe moment of truth for the COBRA robot had arrived.

The wind whipped. The sun blazed. Scree slipped under the feet of the young engineering students from Northeastern University, who were perched carefully on a steep, rocky slope in a desolate patch of California desert.

They activated a program, and the robot snapped into a hexagon shape. Balanced on one flat side and covered in a black sheath, it looked like a skinny tire. Then, suddenly, the bot went careening downhill, bouncing off rocks so fast it launched momentarily into the air—but staying upright and stable through it all.

The tumbling robot was one of seven different machines conceived, designed, and built over the previous 18 months at universities across the