This is by far one of the most engaging quick-start projects I have used in a STEM class.
-3v coincell battery
-Double stick tape
-Blue masking tape
Total cost per Brushbot: $3-5 if buying parts in bulk on Amazon.
Cut the tooth brush handle off (keep for other projects)
Apply the double stuck tape to the top (back) of the toothbrush head
Remove the 2nd protective layer from the double stick tape
Stick the motor and one wire onto the exposed tape
Put the 3V coincell down so the wire is stuck between the tape and battery
When the wire not covered by the tape touches the top of the battery the motor will run
Use the blue tape to make a temporary switch that holds the top wire to the battery
Decorate with google eyes:)