Boston Dynamics founder Marc Raibert calls his company's efforts to deliver a legged reconnaissance robot "basic research." After seeing the mechanized Cheetah in action (see video below), you can see that it is anything but basic. Even though tethered to a treadmill and in the early stages of development, the Cheetah can run nearly 30 kilometers per hour (kph). It may not be able to catch a real cheetah—which can run upward of 120 kph, faster than any other land animal—but Boston Dynamics does plan eventually to deliver a version that can move at a speed of about 80 kph.

When watching Cheetah in action (see video below), notice the flexing and un-flexing of the robot's metallic spine. This is where it really begins to mimic an actual animal and deliver on the promise of speed.

"The spine contributes to the stride length, which is how far the robot travels during one whole cycle of the leg motion," Raibert explains. "The legs only have so much reach themselves, and the spine contributes to the leg motion by increasing the reach and the stride length. The fact that the robot uses a running gait—which means there is a flight phase with all legs off the ground—also contributes to the speed, because the robot can move forward without requiring further motion of the legs. Running fast also requires light-weight legs, with as little mass as possible at the feet, so the forces needed to reverse the motions of the legs is reduced."

A control computer provides stability for Cheetah, adjusting the placement of each foot—how far forward they touch the ground with respect to the hips and body—on each step. "There is also a lot of detailed adjustment and coordination of the back with the legs to keep it stable," says Raibert, adding that his company's Cheetah research is being funded by the Defense Advanced Research Projects Agency (DARPA). "The robot control system, which runs on the onboard computer, measures the pitch attitude of the robot—nose up/nose down—and the height of the robot body above the ground and the forward speed to provide the stability. We did a lot of algorithm development to create the control system that stabilizes the Cheetah robot at these running speeds."

Cheetah uses some concepts from BigDog, a pack-mule inspired bot Boston Dynamics created a few years ago, and other earlier robots they developed. The company's other legged robots are designed to carry heavy loads for troops (the Legged Squad Support System (LS3), a more advanced version of BigDog), squeeze into small spaces where soldiers can't fit (the LittleDog, which resembles, well, a little dog) or trudge through mud and sand (the insect-like RHex).

Although it may be years before any of these bots join their human counterparts in combat, these legged automatons all share a similar goal in keeping troops out of harm's way as much as possible.