We haven't seen much of Boston Dynamic's four-legged self-balancing Big Dog robot since it was last spotted hurling cinder blocks in a lab. And that's maybe because the company's robotic geniuses have been hard at work building a smaller more agile version called Spot that weighs just 160 pounds so it can safely operate both indoors and out.

Powered by an electric motor that keeps a series of hydraulic actuators moving, Spot also features built-in sensors allowing it to automatically navigate difficult terrain. And because Spot is significantly smaller and lighter than Big Dog, it's able to jog along at an impressive pace. It doesn't look like it would be able to carry as much gear and equipment as Big Dog, which is why the quadruped was originally built. But that's probably because Boston Dynamics has built it for different purposes, like search and rescue or scouting, instead of just back-breaking labor.