If you are hiking in the woods of Waltham’s Prospect Hill Park and hear what sounds like the distant whine of an extra-loud chain saw, do not be alarmed. Head toward the noise, and you may encounter one of the world’s most sophisticated walking robots. Big Dog, a canine-like cargo-bot developed by Boston Dynamics Inc., occasionally tromps through the trees on testing missions. Two summers ago, loaded up with extra gasoline, it meandered along for almost 13 miles without stopping.
