Humanity, it seems, escaped the "Terminator" apocalypse: Atlas, the 330-lb. (150 kilograms) robot developed by Boston Dynamics, tripped again — this time during a test at the Florida Institute for Human and Machine Cognition in Pensacola.

But Atlas was never intended for combat. The humanlike robot is a research tool for experiments like the Defense Advanced Research Projects Agency's (DARPA) Robotics Challenge, to be held later this month. The competition "is something like a stock car race, where the teams all use the same vehicle to really test out their skills and approaches," said Marc Raibert, Boston Dynamics' founder and chief technology officer (CTO).

And like any good stock car, Atlas has racked up its share of dings. In October, there were reports that the androidbroke an "ankle"after a fall in Hong Kong. Raibert doubts it was actually damaged, but he does admit that Atlas trips all the time, despite its array of cameras, lidar and force sensors. "That is just part of everyday life developing advanced robots," he said. [Humanoid Robots to Flying Cars: 10 Coolest DARPA Projects]

So, why build humanlike robots? Why not just stick to tracked and flying machines?

Roboticists offered a few explanations.

"We have designed our buildings around the human morphology, and we have designed our tools to be used by human hands," said Daniel Theobald, CTO of Vecna Technologies, a robotics company based in Cambridge, Mass. So a robot that can just as easily use a hammer as it could use a drill is "the ultimate tool changer."

However, that answer may overstate the maneuverability of androids in a human environment. Atlas, for example, cannot sit in an office cubicle or navigate a narrow passage. The explanation also assumes that hands and feet must go together.

Vecna's own Battlefield Extraction-Assist Robot (BEAR) has powerful arms and dexterous three-fingered hands— but no legs. Instead, company engineers have experimented with wheels, treads and tracked actuators that allow the BEAR to climb stairs. The advantage of this design is that it's more stable, Theobald said.

A different explanation offered by Raibert is that wheels require roads, whereas legs can cover all but the roughest terrain. And Atlas, in particular, is being used by DARPA to test robotics solutions for disaster-recovery missions. But why couldn't a legless Atlas just hover over the rubble of a collapsed building?

In the end, there's an element of vanity in this android business, said Rajesh Rao, a computer science and engineering professor at the University of Washington. "We would like to fashion robotic creatures after ourselves," he said.

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