Of course just like nature, the smaller you go, the less power you need for fuel.

See EcoBot 2 a robot capable of powering itself, by ingesting biomaterial from its environment, then converting it into a form of fuel, if you extend this type of system into the nano scale, then what you have is a bunch of self sustaining nano robots capable of total autonomy and god knows where that might lead.

Mad scientist creates Grey Goo, headline 2020?