BigDog was a rough-terrain, four-legged robot developed by Boston Dynamics in the mid-2000s, and the company describes it as “our first legged robot to leave the lab.” Built to navigate uneven ground with a sensor and control system that let it balance dynamically, BigDog established the dynamic-balancing approach that runs through the company’s later machines.
The work grew out of U.S. military interest in a robotic pack animal. DARPA funded the effort in the hope of a machine that could carry a squad’s gear across terrain too rough for wheeled or tracked vehicles, following soldiers like a trained mule. That line of research led to the Legged Squad Support System (LS3), a larger relative that could carry 400 pounds of payload and travel about 20 miles before refueling, with sensors for navigating obstacles. The gas engine that powered these robots was loud, and the military program was eventually shelved, with LS3 put into storage in 2015.
Boston Dynamics frames BigDog and LS3 as crucial milestones whose perception, control, and dynamic-balancing lessons informed its later commercial robots, including the Spot quadruped.
For a general reader, BigDog is where modern legged robotics became visibly real: shaky early videos of a four-legged machine staggering, slipping on ice, and catching itself made the idea of robots that walk like animals suddenly plausible.