A Sh*t-Powered Robot

No, not Mitt Romney.  Scientific American:

The vision of robots capable of plugging themselves into the natural world of living organisms has begun taking shape in several labs around the world, and even NASA has shown renewed interest in powering space robots with microbes. But one British lab has already been building on the work of robotics pioneers to create small "EcoBots" that extract energy from microbial fuel cells since 2002.
"Robots that eat biological fuels could find enough fuel almost anywhere," said John Greenman, a microbiologist at the Bristol Robotics Laboratory, a joint venture between the University of the West of England and the University of Bristol. "There is organic matter anywhere on Earth — leaves and soil in the forest, or even human waste such as urine and feces."
The first EcoBot (created in 2003) was powered by E. coli bacteria feeding on refined sugar. Then "EcoBot-II" (2005) harnessed sludge microbes to break down dead flies, prawn shells and rotten apples. Finally, "EcoBot-III" (2010) showed how a "digesting" robot could also dump its leftover waste, so that its microbes wouldn't be poisoned by their own filth and could keep powering the robot.

I'm pretty proud of that Romney joke.  Anyway, I could power a pretty big robot, and a large-scale dairy could power a freaking army.