Robots don't have to be highly complex androids capable of performing brain surgery or automatons roving distant planets. If a machine is capable of performing a task on its own, no matter how simple, it is a rudimentary robot.
The "bristlebot" is a simple robot to build at home. Bristlebots use the power of vibration to scoot across the floor at high speed, caroming off solid objects.
Snip the bristled end off of the toothbrush with the scissors. Leave around a half-inch of stem still attached to the head for balance.
Lay the bristled head bristles-down on your workspace, and stick a strip of double-sided adhesive to the flat upper surface of the head.
Position the pager/cell phone motor at the end of the toothbrush head opposite the snipped-off stem.
If you don't want to cannibalize a cell phone or pager of your own for the motor inside, you can buy the motors on eBay pre-isolated for very little .
Make sure the motor's turning shaft is sticking out over the edge of the toothbrush head, and press the motor down against the sticky tape to secure it.
Solder two half-inch lengths of small-gauge copper wire to the motor's terminals, and bend one of them down to contact the sticky tape.
Stick the coin cell battery down flat on top of the bent-down wire. Press firmly to secure a good connection.
Bend the second wire down to contact the top of the battery, and your bristlebot will begin to vibrate wildly. Set it down on any smooth surface, and watch it go!
- toothbrush image by Nicola Gavin from Fotolia.com