One of the simplest toy car engines is the pullback racer. They rely on rubber bands, which work by returning to their original shape after being deformed--this is called elasticity--the spring is attached to the rear axle, and pulls the car forward as it returns to its original shape. Here are two methods for building a pullback racer: one using Lego parts, and one using common household items.
- Skill level:
- Moderately Easy
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Things you need
- Elastic Band
- LEGO pieces
- LEGO Technic rods
- LEGO gear
- LEGO Wheels
- Paper and pencils or something to act as a frame
- Dowels and straws, or some kind of axle
- Small paper clip
- 4 wheels
Stick an elastic band around the 2x6-knob plate.
Assemble a frame that will fit the motor and the car. Attach two 1x10-knob or 1x14-knob pieces with side-holes parallel to each other on your 2x6-knob plate.
Push an axle through the rear set of side-holes, with the gear in the centre of that axle.
Attach the rear wheels to that axle. Make sure you use wheels that are larger than the centre gear.
Attach the front axle and pair of wheels to the car through the front-most set of side holes.
Stretch the rubber band from the centre plate around the back edge of the gear. Make sure the band catches between two teeth on the gear, and hold the rear wheels so they don't roll.
Pull the car backwards. The elastic band will pull itself around the gear and wind itself around the rear axle. Don't pull too far or the elastic may snap. Hold the rear wheels until you're ready to race.
Bring the car to a flat surface, line it up and let it run.
Building a LEGO car
Align the page so the long edge is facing you, then fold the left side to the right edge, and glue the page down. Leave it for a few minutes to dry.
Fold the paper again in half, so the folded edge aligns with the opposite edge, and glue the page down a second time. Glue it and leave it to dry.
Tape or glue two pencils to the page to make a frame.
Cut a 1-1/2-inch square notch out of the back end of the paper.
Cut two straw segments as long as the car is wide. These will hold the axles in place.
Glue the axle holders in place. One should be about an inch back from the front of the car, and the other about 3/4-inches from the rear of the car, on either side of the notch. Leave this to dry for a few minutes.
Trim the middle out of the rear straw segment, taking care not to remove the straw altogether.
Remove one of the metal arms from the paper clip and loop the elastic band around it, then return it to the clip.
Attach the paper clip to the front of your car, and move the arms to the closed position. Take care not to crush the front axle.
Cut two lengths of dowel to exceed the width of the car by about 1/2-inch.
Glue or connect the dowels to one wheel each.
Slide the dowels into the straws at the bottom of the car.
Glue or connect the other wheels in place.
Pull the rubber band back to the rear axle. Tape or staple it firmly to the midpoint of the axle.
Pull back the racer, and release it to send it rolling.
Building a Paper Car
Tips and warnings
- If you pull the car forward, it will roll backwards.
- The cars described above are examples, and the motors made here will work in a wide variety of car shapes and sizes.
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