Mark Grossmann: Robo-Cheetah & its Little Sister, the Wildcat

6 February 2014

Developed for DARPA by Boston Dynamics, the robo-cheetah’s claim to fame is its speed.  Modeled after the real-life cheetah, this robot boasts a “cat-like spine,” which “flexes and extends” with the robot’s galloping stride. And it gallops — “constantly tipping forward, falling, and regaining equilibrium with every step.”  After the development of the first prototype, in 2011, it was showcased running at speeds of up to 18 mph by March of 2012.  By September, it clocked 28.3 mph – faster than the fastest human runner in a hundred-yard dash.

Of course, with all the excitement, Robo-Cheetah still had a couple issues that needed to be ironed-out before it could go bounding across a battlefield.  It was running at high speeds, but it was only running on a treadmill.  Still, it was about ready to jump off the treadmill and onto, at least, flat ground.

It’s biggest problem was that it was still “tethered” by a power cord.  In other words, it had to be plugged into a wall socket to get the juice it needed to move.   There’s no portable power pack for this ‘bot that can store enough juice to let it run free.  Portable power supplies are a big issue in robotics and one of the biggest challenges to maximum performance.  There’s a tradeoff.  You need enough power to allow the ‘bot to operate for long stretches of time.  You, also, need a power pack that’s light-weight enough for the ‘bot to carry.  But, with a light enough pack, there’s not enough power to run the ‘bot.  And, with enough power, the pack (and ‘bot) become so heavy that, now, . . . there’s not enough power.

But, soon, there were more than these technical challenges – there were challengers.   The first competitor was MIT. The Biomimetic Robotics Lab at MIT, also under the sponsorship of DARPA, was, and is, working on its own version of the robo-cheetah.  MIT is trying to recreate the running movement of the real cheetah.  They’re more public with their work.  The MIT website shows their version of Robo-Cheetah.  Their robot can’t run as fast as the Boston Dynamics model, but MIT’s model boasts a “highly efficient leg motor, imitation tendons, and a responsive tail.”  With these improvements MIT’s Robo-Cheetah has a rhythm and movement completely different from other four-legged ‘bots.

MIT’s Robo-Cheetah, also, “will” run on a battery (but it, too, is still plugged into a wall-socket).  Unlike the other Robo-Cheetah, MIT’s uses a surprisingly simple and more effective way of regulating its leg motion – one without the usual sensors and complicated computer feedback-loops that were, and are, still a common part of robotic technology.

But what’s so important about imitating a real cheetah?  The robo-cheetah is one of a group of DARPA-funded projects of applied biorobotics.  To meet DARPA’s requirements, drones must be built to perform more like . . . wildlife.  The term “biomimetics” or “biomimicry” is used to describe the development of technology designed to imitate and replicate the activities of biological systems and organisms.   But, why imitate nature?  Well, “if you want drones that work in a particular way, and the only known example of such performance is a biological organism, you’ll either have to imitate it or forget the project altogether.”

The need for walking (rather than rolling) robots is a prime example.  The jeep took “a basic automobile and raised the center of gravity, increased the size and scale of the automotive suspension system and produced spectacular off-road performance for a machine with wheels.”  But the wheel, itself, was limited.  Human beings, horses, mules, and dogs can all travel over terrain that would be impossible for any wheeled vehicle to handle.

How do you design a ‘bot that travels over rough terrain like a mule?  Well, you design it . . . like a mule.  And Boston Dynamics “Robo-Mule” (later, renamed “BigDog”) was the first in a new line of bio-inspired “walking” robots.  But, again, why a cheetah?  Is it just a cool sounding name, or the sleek look of the moving animal? No. There’s something special about cheetahs that DARPA wants to capture in robotic performance.

Robo-cheetah is being designed to move, quite specifically, like a cheetah.  Unlike Robo-Mule (“BigDog”), Robo-Cheetah is meant to be ultra-speedy and agile, able to “chase and evade” like the actual animal.  Designers are working on getting it to run at Cheetah speed, but their ultimate ambition goes much farther than that.  They hope to design a ‘bot that can run faster than any animal on earth — as fast as 70 mph.

Robo-Cheetah will have clear military applications, including emergency and disaster response.  But DARPA has hinted at performance that might improve on nature.  At least, humans might be able to do things with Robo-Cheetah you’d never try with the real thing – including uses in “advanced agriculture and vehicular travel.”  Just think.  Riding a Robo-Cheetah!

Of course, the pressure rose with two Robo-Cheetahs in development: The speedy one by Boston Dynamics and the graceful one by MIT.  But, the race got even tighter when another competitor came out of left field — the Robo-Ostrich.  Ostrich?  What’s an ostrich got to offer in this race?  It’s a bird, and it can’t even fly.  Well, fly it can’t, but maybe it doesn’t need to because the ostrich is the fastest land animal on earth.

DARPA has funded the joint effort of MIT and the Florida Institute of Human and Machine Cognition (IHMC) in a project to develop a robot that walks and runs.  But the end result of this latest effort will be the first robotic biped in the DARPA arsenal.

Robo-Ostrich is designed not just to walk, but to run and run fast.  Although the first full prototype has yet to be designed, the working computer simulation has legs and is hitting speeds of 27 mph.  Impressive, again, because this is about the speed of the fastest human runner in a hundred yard dash.

Robo-Ostrich’s designers are only hoping for a maximum speed of 50 miles an hour – faster than the fastest ostrich clocked at 43 mph.  On the other hand, this is a bit slower than the 70 mph Boston Dynamics is hoping for Robo-Cheetah.   But there’s a whole ‘lot of hoping going on here.  Robo-Cheetah isn’t off the treadmill and Robo-Ostrich is a computer simulation.  Let’s just wait and see.

What’s the secret of Robo-Ostrich’s speed?  Two legs.  What’s so special about a two-legged robot?  Not only is a two-legged robot lighter than a robot with twice the legs, but its movements are more flexible allowing it to, among other things, “get through narrower spaces” and maneuver more easily around obstacles.  With such a flexible build, this robot, like other “be-footed” robots, is designed to negotiate rough terrain that would defy a wheeled-vehicle like a jeep.  Even on the most irregular surfaces, the finished ‘bot is expected to run (or walk) at a speed of 10 mph, more than twice as fast as a walking human being.

Well, with MIT pushing hard to the goal with both their robots, Robo-Cheetah and Robo-Ostrich, Boston Dynamics had to do something.  They announced their plan to take the lead in the race, by unleashing Robo-Cheetah from its treadmill.  They promised their Robo-Cheetah, unteathered, would hit the road in 2013.   And it did, but with a twist.

In 2013, the cordless “Wildcat” was shown galloping and running backward on flat terrain.  But, wait, what happened to Robo-Cheetah?  Why the little sister?

To speed up the development, Robo-Cheetah was . . . modified.  To get rid of its power cord and, then, off the treadmill and onto the ground, it had to lose some of its bulk and weight.   It also lost its electric motor and gained an internal combustion (gasoline powered) engine.   Even with the reductions in size and weight, it lost some of its treadmill speed — slowing from 28 to about 16 mph.

Now, it’s slower than the fastest human in a hundred yard dash. But, if its chasing you, you’d better get to safety in a hundred yards. Why?  Because the Wildcat will still be going strong and fast long after you’ve given out and fallen to the ground.

The Wildcat still only performs on flat terrain, but the plan is to, soon, have it walking on the same rough ground that its distant cousin the Robo-Mule/BigDog handles with ease.

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