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How would you create a pull back car using rubber bands cardboard and wheels?

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March 31, 2008 12:31AM

It may be wisest to build around the wheels. They will determine what axles you'll use. The wheels will have to be fixed on the axles so there isn't any slip. The rest of the car will be constructed around these parts. This approach will arguably be the easiest and yield the best results. Take a small cardboard box and turn it upside down and you've got a car body. Poke two pairs of holes through the sides of the box near the bottom (the open) side at appropriate points where the axles will be placed. This sets up the wheelbase of the vehicle. The back axle and wheels will be a solid, non-moving assembly. You'll need a place on that axle to "grab" the rubber band. A projection. And it should be a bit offset from the middle, but not clear out at the edge. You have a couple of choices. One is to clean a bit of the axle off to bare metal and solder on a little "L" (with the "long" side against the axle for strength). Or you might be able to wrap a short piece of heavy wire around it and leave a bit bent out. Then super glue or hot glue the coil of wire around the axle so it won't slip. It must not. Perhaps some wheels and a wooden dowel are used. A very small hole could be put in the axle and a little bit of something like a coat hanger could be put through if this can be done without breaking the axle or compromising its strength. Or just hot glue the end of the rubber band to the axle after it's all assembled. Or twist a bit of fine wire around the rubber band to anchor it to the axle. It mustn't slip. The end result is that the axle needs to have a little projection out from it to hook on the rubber band or the band needs to be firmly attached to it. Just tying the rubber band to the axle might work if hot glue is used to keep it from slipping. Energy will be stored in the rubber band either by "wrapping" or by "twisting" the rubber band. Twisting energy is much more difficult to transfer into the axle - unless you have a gearbox. (Twisting is used to store the energy in the propellor driven rubber band airplane.) Want it that complex? Got the parts? If not, wrapping the rubber band around the axle to store the energy is probably the choice to make. The rear axle will have to be installed on the car before the "projection" where the rubber band is gonna be hooked is installed. Or, if the band is going to be twisted wire and glued to the axle, that axle is still gonna have to be installed first. You'll need a "hook" on the inside of the box at the front of the car to anchor the other end of the rubber band. The rubber band shouldn't have much (if any) slack in it when everything is put together. It'll be important to pick it carefully before hand, particularly if it's attached through glue or whatever to the rear axle. Don't pick too wide a rubber band. You'll need some small "spacers" between the wheels and the body to keep the wheels from rubbing on the cardboard of the body. Use a small piece of a drinking straw or something if you have to. Think about it and find an appropriate spacer material. Put in your front axle. Install your spacers and your wheels making sure everything is solid. Connect your rubber band to the anchor and the rear axle (if it isn't already), pull it back to wind the rubber band around the axle, and let it go on a flat surface. The car's performance will be as sophisticated as the construction materials and techniques. For instance, if one put holes in the body where the axles went through and glued in a piece of straight, hollow, small-diameter pasta for axle bearings, it would work better. Obey all local speed laws and operating restrictions. Oh, and good luck.