Quadruped Robots > Big Dog
BigDog, a creation of Boston Dynamics, is the poster child for quadruped robots. A large, bulky pack-bot, it is designed to go anywhere a human soldier can go, walkingh across any terrain, with four firm feet. It can walk on almost any surface, run on those same surfaces, recover from being whacked hard when standing still or running, and carry half a tonne with every step whilst it does all this.
Unsurprisingly, BigDog is a military robot, designed to aid squads of troops in the battlefield. Its three feet in length, one foot wide, two and a half feet in height, and weighs in at 240 lbs, plus equipment which can weigh up to 340 lb itself..
BigDog's legs are articulated, well, like a dog's. They absorb the shock of impact with the ground, then recycle that kinetic energy for the next step. In profile, it almost resembles two pairs of human legs, facing one another, with a large load between them.
The bot is capable of running at up to 4mph, which doesn't sound like much, until you remember that it can sustain this 4mph or something close to it, on loose sand, rock, snow, wading a stream, tangled vegetation or tarmac, and keep it up whilst transitioning between them. Slopes do slow it down, of course but it can still scrabble its way up a 35 degree incline, which is about the limit for a walking human too.
BigDog has about 50 sensors. Inertial sensors measure the attitude and acceleration of the robot itself, responding in such real-time that a researcher, squarely shoving the robot with his upper body strength, was unable to get it to tip - the robot shot out a foot and compensated long before it was in danger. Even if it does fall, the robot can pick itself up, eventually, as it is impossible for it to rest on its back.
In addition to the inertial sensors, other sensors monitor BigDog's hydraulic pressure, flow and temperature, engine speed and temperature, etc.
Joint sensors measure motion and force of the actuators working at the joints.
As a side effect, this gives BigDog a crude sense of proprioception - it knows
where its body parts are in relation to each other, at all times. Because of
this body-sense, a range of behaviours has been developed. Currently, these
include standing up, squatting down, crawling along, shifting one leg at a time,
walking like a dog, trot like a horse, for a cantering gait between walk and
run, run like a (slow) cheetah. Additionally, it can gallop with small bounds,
ideal for clearing a crevasse, although actual jumping - from one height to
another - is not yet possible.
Of course the one problem it does have, in current models, is the whine of the diesel engine, kinda lets the enemy know its coming. Sneaking up is not something BigDog has mastered, yet.