Big Dog

BigDog was developed with funding from the U.S. Defense Advanced Research Projects Agency (DARPA) as a robotic transport platform designed to accompany infantry across rough and uneven terrain. Its original powerplant was a 15-horsepower, two-stroke, single-cylinder gasoline engine, spinning at 9,000 RPM to drive a hydraulic pump. The resulting hydraulic pressure powered sixteen actuators—four on each leg—giving the machine its remarkably smooth and dynamic gait. The distinctive, high-pitched mechanical roar heard in early footage came largely from its two-stroke engine. Later iterations became considerably quieter as the powertrain was upgraded. BigDog was equipped with contact sensors in its feet for balance and posture control, while a laser gyroscope and stereo vision system allowed it to perceive the terrain and compensate for changes in ground inclination. But the machine had one critical flaw. Its acoustic signature proved difficult to conceal in a battlefield environment. Its engine noise could potentially give away the position of friendly forces to the enemy, making stealth and tactical deployment difficult. Development of BigDog was eventually discontinued, and its intended role was passed on to its quieter successor, Spot.