How cool is this! Here we have a hybridized robot, which uses a small four-stroke engine made by Subaru/Robin powering an automobile alternator which in-turn offers up the power for the robot. A small 12-volt battery pack smooths out the voltage to the motors. The alternator reportedly puts out at least 25 amps, which is more than enough to power a small outdoor robot such as this one. For those keeping track of such things, this robot is an example of a series hybrid, like the proposed Chevy Volt and various trains. Unlike a parallel hybrid, such as the Toyota Prius, the engine has no mechanical connection to the wheels and is therefore not capable of providing any direct power to the wheels. Which approach is better is a topic in and of itself, and the reason the serial approach was chosen for this robot is for simplicity.
[Source: Hack A Day]