This was one of my first excursions into building a useful or interesting electronic thing for the kids to play with. The idea is really simple, use the vibrations from a motor to shake a yogurt pot with pens on it. The result should be some interesting patterns drawn on paper (and probably the floor).
I sourced the motors from some dollar store fans and a Nintendo rumble pack (found for $1.50 in a thrift store). The fan motors were great as the were already wired up to a switch and all I had to do was solder on a battery pack. I glued the battery pack on the insides of the pots and poked some holes in the top to attach the wires to the motors. I then weighted one of the fan blades with glue to set up a weight offset and increase the amplitude of vibration.
We made a mistake with the first plastic pot in that we glued on the pen legs to the pot, which meant that they weren't easily changeable (not for kids anyway). I say "we" because the gluing was done by my wife, who is far more adept with a glue gun that I am. 'er indoors also had the idea of putting in some motion activated flashing lights scavenged from various kiddie toys and gluing them onto the inside of the pots. That was a nice touch; thanks love!
For the second pot we glued on the pen lids instead:
For some reason this larger one reminds me of those ships in Tron...
It turns out that the results from the drawing actually makes for some good wrapping paper! Bonus!
And, finally, a little video: