In 2008, the Robot Hall of Fame inducted the Raibert Hopper, a one-legged robot that Marc Raibert used for experiments on dynamic balance. The Hopper showed that robots, like humans, could rely on motion for stability and suggested that robots might someday display the same agility as humans.
Big Dog demonstrates why the Hopper's achievements were so important. Built for the Defense Advanced Research Projects Agency in 2005 by Boston Dynamics, a firm co-founded by Raibert, Big Dog is a dynamically stable quadruped robot. Envisioned as a robotic pack mule for soldiers, it can traverse difficult terrain, climb a 35-degree incline and run at 4 miles an hour while carrying 340 pounds.
Millions of people have gawked at YouTube videos of Big Dog, showing the machine getting kicked sideways, yet somehow keeping its feet. Big Dog may not have the grace of an animal – yet – but its gait looks more like that of a dog or a goat than it does the stereotypical, plodding robot.
The success of the program led DARPA and Boston Dynamics to develop a larger, more robust version called the Legged Squad Support System, or LS3.
Raibert, speaking at the induction of Big Dog into the Robot Hall of Fame, declared Big Dog "is my favorite robot child." The project re-focused his company on robotics, he noted, and got researchers out of pristine labs and into the rocks, mud and dirt of the field. But most of all, Big Dog represented "light at the end of the tunnel." He explained:
"After years of doing pure research, where all we were trying to do is make progress getting robots to be a little bit better, to do the next trick, there was a time in the development of Big Dog when we realized – Holy cow, this thing could actually work. You could really take a dynamic, actively balanced legged robot out into the world and it could do useful, practical applications. And that's a very exciting thing."