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.
After years of building small robots (see here: http://www.instructables.com/id/Building-Small-Robots-Making-One-Cubic-Inch-Micro/) , I decided the only way to make the smallest robots possible, was to have the motors, batteries, and even the Picaxe microcontroller external to the robot.
pic 1 shows R-20 a 1/20 cubic inch robot on a dime.
pic 1b and 1c shows smallest wheeled robot lifting and holding an 8 pin IC.
THERE IS A VIDEO in step 3 that shows the robot picking up an 8 pin IC and moving it.
And another video in step 5 that shows the robot turning on a dime.
Step 1: Tools and Materials
Micro serial servo controller available from Polulu: http://www.pololu.com/
2 high torque servos from Polulu
2 standard servos from Polulu
.oo5" thick copper, brass, or phosphor bronze sheet metal from Micromark
2- 1/8" x 1/16" neodymium magnets
1- 1"x1"x1" neodymium magnet. Magnets available from: http://www.amazingmagnets.com/index.asp
Telescoping brass tubing from Micromark: http://www.micromark.com/
Brass pins from Walmart
Glass beads from Walmart
1/10" fiberglass circuit board material from Electronic Goldmine: http://www.goldmine-elec-products.com/
clear five minute epoxy
Assorted nuts and bolts
small needle nose pliers
Pic 2 shows the Picaxe module used.
Pic 2b shows the back of the Picaxe module.