these are the most fun to make when you dont have any money :)
I ran out of pager motors so I just used a zip tie as the counter wieght it works great :)~Matt
I salvaged it from an old motherboard, it was the system battery.
I made seven so far, and I have a video somewhere on my computer of all 7 in an enclosed wooden "arena" and me turning them all on at once, it looks pretty cool.
One two of them I added an OpAmp and 1 bumper switch so that when it touches something it completely stops
I've been collecting old cellphones to pillage vibration motors from in hopes of building a bristlebot army!
Would love to see pics of yours ;)