Toothbrush robot is the most basic and simplest robot to start with.
Kids can build them. So I supervised my son to build one...
Video link :
Step 1: What Do We Need ?
1. Old toothbrush
2. pager vibrator
3. 3v battery
4. double side tape
I extracted vibrator from Wii remote. one can buy it too
Step 2: Assembly
I cut the three toothbrush as shown.
Using double sided tape stick vibrator and battery
Put one wire below the battery and other on top. used electric tape to stick it
Step 3: Decorate
Used the car from the toothbrush to decorate it. it made it but slow....
My son enjoyed making it
I did this with DC motor with other kids they also liked it