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How a Rubber Band Powered Car Was Built

This is how a rubber band powered car was built for a school assignment.

It started out where a small soap box derby car wa bought to get the progect started. Of cource, the car sat there until the last minute when the assignment was due the next day and that is when the construction began. The rules stipulated that only household materials could be used except for the wheels. The construction began by cutting two rectangle lengths of cardboard and gluing them together to form the floorboard or frame of the car. It should be noted that since the car was due the next morning, the only glue used was a generic "Super Glue" that was rated for a drying time of 30 seconds. Also, the glue was the thick version because of the porous nature of the cardboard. (Which came from a real strong Canadian Mist Liquor box.) The doubled cardboard made the frame stronger and better supported the wooden dowel.
The Canopy for the car was half of a thin plastic, disposable Coke cup that could be cut precicely using a pair of straight cutting tin snips. The half with the logo facing upwards was used so that it would become part of the decoration. The canopy was not glued on till late in the construction as the dowel hole had to be drilled.
A reasonable fat woden dowel was inserted into a drilled hole completely through the floorboard. The dowel became the rubber band anchor point.
The tricky part was the rear drive system. Soap box derby wheels are supposed to spin around a fixed axle and the car is supposed to be powered by gravity. But in this car, there needed to be a fixed axle attatched to the rear drive wheels so that when the rear axle spun, the rear wheels would then spin too. In order to have an axle, A way to support the axle was needed so vertical supports were made from additional plastic cup bottom halfs. Originally, it was thought that the axle would go above the floorboard. But because the little tiny black plastic wheels were so short, the axle assembly was put beneath the floorboard for clearance. A hole was very carefully and very slowly cut by twisting a drill bit with the fingers so that a nice round hole would be produced in the thin plastic cup material. This took a couple of tries to perfect. The cup bottoms were glued opposing each other and the axle was placed through the holes to ensure that there would be no binding. The axle has to spin freely inside the holes of the vertical axle supports.
Eventually, the plastic wheels were nailed and superglued to the ends of the axle dowel after the axle dowel was inserted into it final position. But before that, it was anticipated that the axle had freeplay where it would shift from side to side during operation. This would mean that the inside of the rear wheels would rub against the floorboard of the car causing drag. And that would be bad. So, a very carefully placed notch was cut into the axle. A very shallow notch resembling a groove was cut to allow for a left/right axle sway guide.
Another small piece of plastic cup bottom was glued under the axle in such a way that a virtical piece of plastic would ride inside of that axle groove. The plastic finger was thin and flexible to give the axle a little play but not enough to let if go too far.
Rubber bands were interlooper together to form a longer rubberband.One end of the rubber band was wrapped around the axle in the opposite direction of the tention that would be later applied to it and the front end of the rubberband was looped around the anchor pin previously mentioned. The rubber band was not permanantly attatched to the anchor pin because if it were, the rubber band would act as a brake once the energy of the rubberband was depleted. So instead, the rubberband was held in place by tention at first. But as the energy of the rubberband was all used up, gravity would allow the rubberband to fall off the anchor pin and allow momentum to carry the car even further foreward while the spent rubberband wound up harmlessly around the rear axle.
The front axle was glued to the floorboard while the front wheels were allowed to spin freely around the nails they came with. (the axles they were designed to use.) Extra cardboard was glued near the front of the car to increase the gluing surface for the front axle.
The initial tests of the car once everything was assembled revealed that the car has a huge amount of power and no traction at all because the plastic wheels were very slick. The car just sat in one place while the rear wheels did a burn-out. To compensate for that, the rear of the car, over the rear axle was declared a cargo area and weight was added. Cans of Chunky soup and a 16oz diet coke bottle (both full) were not heavy enough to improve the traction and the car still sat in one place while the rear wheels spun nderneath it. The problem of poor traction was overcome by supergluing a rubber racketball to the outer rims of the small plastic wheels. The weakest part of the rear axle was the inner rim area there the rear wheels joined the wooden dowel because it has the smallest surface area for gluing purposes and all of the torque from the wheels had to pass through that point and into the dowel. But, it helt together. The rubber of the racketballs proviced traction and the increased diameter of the balls changed the gear ratio positively. The car became fast and powerful enought o carry cargo. The balls also gave the car a higher stance in the rear for a hotrod posture.

Click photos for better view.

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This car traveled farther than any of the other cars and received an A.

 

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