Extreme Science: Penny Shine

What you will need:

  • New toothbrush
  • Clippers
  • Sandpaper
  • Double sided foam tape
  • Small button battery
  • Small electric motor
  • Wire strippers
  • Pencil eraser
  • Tape
  • Adult supervision


  • Pipe cleaners
  • Peel and stick decorative eyes


1. Start by carefully cutting the head off of your toothbrush with your clippers

2. Sand the cut edge if necessary

3. Cut and place a piece of foam tape on top of the toothbrush head as shown:

4. Tear the eraser off the end of a pencil and place it on the shaft of your motor so that it is off-centered as shown:

5. Stick motor to the top of foam the tape making sure that the eraser is hanging out over the edge far enough that it will not hit the body of the toothbrush head when motor is running. Stick one of the wires down on the top of the tape as shown.

6. Stick the button battery down to the tape so that it is in contact with the wire that is already stuck to the tape.

SAFETY NOTE: These small button batteries can be lethal to small children if swallowed. Please make sure that they are not accessible to any child that may put them in their mouth!

7. Place a small piece of tape over the remaining wire so that you can stick it to the top of the battery to turn your bristle bot on. Simply remove the wire from the top of the battery to turn it off.


You can use items such as pipe cleaners and stick on eyes to decorate your bristle bot as shown. Get creative to decorate your bristle bot to make it your own creation!

What is going on?

Motors are balanced so that they will run smoothly. By placing the eraser on the motor shaft so that it is off-centered, the (unbalanced) weight of the eraser will cause vibration as it spins around on the motor shaft. This vibration will cause the body of your bristle bot to move rapidly back and forth. As the body moves, a force will be applied to the bristles of the toothbrush, which are holding up your bristle bot. This force will cause each bristle to bend slightly creating what is called potential energy. This potential energy will be stored in each bent bristle and, as the weight of the eraser is shifted again, this energy will be released in what is called kinetic energy as each bristle springs back into a straight position. This release of energy is what causes your bristle bot to move across the floor.

Try this:

Try placing the motor in various positions or directions to see if it makes a difference as to which direction your bristle bot moves along the floor. What if you switch the wires around so that the motor runs in the opposite direction? Does this make a difference?

Radical Rick

Extreme Science



Recommended for you