From Boston Dynamics BigDog is powered by a gasoline engine that drives a hydraulic actuation system. BigDog`s legs are articulated like an animal`s, and have compliant elements that absorb shock and recycle energy from one step to the next. BigDog is the size of a large dog or small mule, measuring 1 meter long, 0.7 meters tall and 75 kg weight. So far, BigDog has trotted at 3.3 mph, climbed a 35 degree slope and carried a 120 lb load.