The heart of BigDog's power is a cylinder combustion engine which drives a hydraulic variable displacement pump. BigDog can walk at 0.7 m/s over loose rock beds and carried over 50 kg of payload. The heart of BigDog’s power is a cylinder combustion engine which drives a hydraulic variable displacement pump.  BigDog can walk at 0.7 m/s over loose rock beds and carried over 50 kg of payload