This one uses a vibrating motor from an old cell phone, a 3V watch battery, and a paper clip. A little soldering, some hot glue, and you've got a vibrobot!
Step 1: Gather materials
1. A watch battery (I used a 3V, but you can probably use whatever you find)
2. A motor from an old cell phone
3. A big paper clip
4. Soldering iron, solder, flux (optional)
5. Hot glue gun
6. Electrical tape
7. Sharpie or other dark marker
Optional but helpful:
8. Metal file
9. Rubbing alcohol
10. Needlenose pliers for the bending
Step 2: Make the legs - part 1
First, straighten out the clip, then mark out six equal parts. On mine, marking every 1 1/16" worked out fine.
An important note about bending the paper clip -- go slowly! Take a few seconds to make each bend, or it could snap. Also, for the angles that are greater than 90, make them rounded, so there's not so much stress at one point. It took me three tries to finish the legs. (See the last photo.)
Now, bend a 90 degree angle at the first mark.
At the second mark, bend it back completely.