Self-propelled toy cars are a mainstay of science fairs and childhood group parties. While design and propulsion methods vary widely, the most common method is through the use of a rubber band. Some more complicated designs use various types of springs. One can even find self-propelled cars powered by paper clips or mousetraps. All these types are powered by the transfer of some form of mechanical tension. But you can very simply make something that operates on a completely different principle and stand out. The principle is jet propulsion.
- Skill level:
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Things you need
- Wooden car kit
- 2 small metal washers
- Various long balloons
- Clothes pin or flat-edge hair clasp
- Cotton-tipped swabs
- Whittling knife
Set the wood block from the car kit in front of you. Midway down what will be the back of the car, drill a 1/4-inch hole at a 45-degree upward angle, so that the drill bit comes out at what will be the top of the car. Glue a metal washer around the entrance and the exit hole. Allow to dry.
Carve the block into the car shape that you wish.
Insert the axles into the front and rear of the block and attach the wheels. Some kits have pre-drilled holes for the axles. If yours does not, use the narrowest drill bit you have to drill out holes for the axles.
Use a cotton-tipped swab to push the balloon through the hole in the back of the car so that the body of the balloon is on top of the car while the aperture remains at the back. You will need a balloon that is long enough so that most of it hangs out of the top of the car. The aperture should be big enough that it does not slip through the hole you drilled.
Blow the balloon up through the back of the car. The balloon will swell into its natural shape atop the car. When you are finished, affix the clothes pin or hair clasp to the balloon aperture at the back of the car to keep the air from rushing out. Set the car wherever you want to send it, release the clothes pin or clasp and watch it go.
Tips and warnings
- Try different types, shapes and sizes of balloons to see which sends your car the furthest. Heavier gauge balloons usually give the best results. You can experiment with graphite and mineral on the axles to make it run quicker and smoother.
- If you use a balloon that is too small, it can just go flying out of the top of the car without propelling it. If you have a problem with it happening frequently, you do not have to start over. Simply glue a washer with a smaller aperture over the original on the back of the car.
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