Build a 1/20 cubic inch robot with a gripper that can pick up and move small objects. It is controlled by a Picaxe microcontroller. At this point in time, I believe this may be the world’s smallest wheeled robot with a gripper. That will no doubt change, tomorrow or next week, when someone builds something smaller.
The main problem with building really small robots is the relatively large size of even the smallest motors and batteries. They take up most of the volume of a micro robot. I am experimenting with ways to eventually make robots that are truly microscopic. As an interim step, I made the three tiny robots and the controller described in this instructable. I believe with modifications, these proof of concept robots, could be scaled down to microscopic size.