A vibrobot is perhaps one of the quickest and easiest bots that you can build. In almost no time you can make a fun little bot that makes its ways to and fro across the floor. It is so easy, in fact, that it wouldn't be hard to make a few at once. And then, you can have your own mini private army of vibrobots to do your bidding (assuming that your bidding is to have a bunch of tiny little bots moving randomly to and fro).
Step 1: Go get stuff
Step 2: Strip wires
Step 3: Solder
Solder the black wire to the ground (minus) pin of the battery holder.