But what's a robot? Is a 3D printer a robot? (it has moving parts and builds things) is the Google Adwords code a robot? (it sure makes a lot of money) a quant hedge fund? Do you tax all computers by cost or value produced?

Seems simpler to tax companies for making money.

EDIT: We won't need middle-manager bots that show each other powerpoints all day. What "robot" would get taxed for the disappearance of that function?