The Defense Advanced Research Projects Agency continues work on its Cheetah robot, which this week broke its own land speed record of 18 mph.

The Defense Advanced Research Projects Agency (DARPA) and Boston Dynamics have unleashed a legged robot that's even faster than Olympic champion Usain Bolt.

The Cheetah recently broke its own land speed record of 18 mph, running a 20-meter split at 28.3 mph, faster than the world record for a human set in 2009 when Usain Bolt reached a peak speed of 27.78 mph.

But that accomplishment comes with a caveat, DARPA admitted in a news release. The robot had a slight advantage over Bolt, since Cheetah ran on a treadmill which provided the equivalent of a 28.3 mph tail wind. Still, most of the machine's power was used to swing and lift its legs fast enough to achieve its quick pace, not to propel itself forward, the agency said.

Under development in the Maximum Mobility and Manipulation (M3) program by Boston Dynamics, the animalistic robot is based on the world's fastest mammal. Like a real-life cheetah and other swift land runners, it's built to be able to navigate difficult terrain that cyborgs riding on wheels or tracks can't.

"The most difficult terrain demands the use of legs, as legs can step over both high obstacles and deep ditches," DARPA said. "But coordinating the swing and lift of mechanical legs is more difficult than making wheels turn or tracks roll, and previous legged robots have been slow compared to wheeled or tracked ones."

DARPA's goal is to create legged robots that don't sacrifice speed for mobility on rough terrain.

"Modeling the robot after a cheetah is evocative and inspiring, but our goal is not to copy nature," DARPA program manager Gill Pratt said in a statement. Instead, the agency is attempting to understand and engineer robots to duplicate certain core capabilities of living organisms, like efficient locomotion, manipulation of objects, and the ability to adapt to environments, Pratt said.

One day, the agency hopes to let Cheetah loose in the natural and man-made environments where defense personnel operate, allowing the robot to contribute to emergency response, humanitarian assistance, and other missions.

DARPA plans to test a prototype in the field next year, pulling Cheetah off of its current treadmill regimen and running it through natural terrain.

Powered by an off-board hydraulic pump, the robot has increased its speed since DARPA last released results in March, thanks to improved control algorithms and a more powerful pump.

"The robot has a ways to go before it can come close to matching the speeds of its living and breathing cheetah kin (the Cincinnati Zoo's cheetah, Sarah, was recently clocked at 61 mph), but that really isn't the point," DARPA said in its release.

For an up-close look at the Cheetah robot gaining speed on a treadmill, check out DARPA's video below.