my own take on the classic bristlebot, with a 3D printed battery holder.
1 vibration motor
1 CR2032 battery
step 1: cut the head of a toothbrush
step 2: print the battery holder
step 3: attach the vibration motor to the battery holder and put the 2 leads into the holder block so the battery can touch it.
step 4: hotglue the holder to the toothbrush head
step 5: cut (if needed) the toothbrush hairs to length and bend them backwards so the bristlebot will go forward instead of in circles.
step 6: decorate and race!