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How to Make a Rubber Band Engine for a Bottle Boat

One of the simplest ways to power a homemade toy is with a rubber band. Although it is a low-tech power plant, it serves as a useful demonstration of how more sophisticated devices work. Like an electric motor attached to a battery, it uses stored energy to provide the toy with motive power. The only difference is that the stored energy is created by the rubber band's own elasticity. To power a bottle boat, you can insert a paddle wheel into a rubber band and wind it tightly to generate propulsion.

Things You'll Need

2 12-ounce plastic soda bottles
2 2-inch cubes of wood or styrofoam
Waterproof tape
Heavy rubber band
1/8-inch balsa wood
Hobby knife or box cutter

Instructions

- 1
  Lay the two soda bottles side by side on a clean work surface, with the two blocks of wood or styrofoam nearby.
- 2
  Position one block between the two bottles as a spacer, near the bottom of the bottles. Wrap the two bottles and the block with waterproof tape, so that the block is held tightly in place.
- 3
  Repeat the process to secure the second block at the shoulder of the two bottles, near the top. This creates a catamaran hull, with a 2-inch gap between the hulls and a wider gap between the necks of the bottles.
- 4
  Stretch a short, heavy rubber band between the necks of the two bottles, to act as the engine.
- 5
  Cut two 4-inch by 2-inch rectangles from a sheet of 1/8-inch balsa wood, using a hobby knife or box cutter. At the midpoint of each piece, cut a narrow 1-inch notch. Cross the two pieces at the notches, to make an X-shaped paddle wheel.
- 6
  Insert the blades of the paddle wheel into the rubber band, so the band passes between the blades on opposite sides. Wind the rubber band several times, to create tension. Place the boat in the water and release the paddle wheel. The rubber band will unwind, powering the boat.

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