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, Tue, 25 Jan 2011 07:42:15
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I believe you can make the car any shape you want. The most critical thing is prepping the wheels and balancing the weight. You can't spend enough time on this. My oldest son made a van. Basically knocked the front upper edge off to make a windshield and left the rest of the wood block alone, and he came in second one year with it--I was dumbfounded.
Surface friction is your real enemy. We chuck the axles in a drill and cut several grooves along them with a triangle file. This helps hold the powdered graphite and creates less friction against the inner chamber of the wheel. We soft-taper the flat side of the axle/nail head and smooth any casting burrs to make less surface area against the outside face of the wheel. We also use a tap on the inside of the wheels to make groves to hold the powdered graphite and make less flat surface. The wheels get deburred and polished on the outside. Mount them in the car with the axles pointed very slightly upward. This forces the wheel outward away from the car--less rubbing--and makes the wheel ride only on the very inside edge, not the whole flat wheel surface. They also stay very stable and don't ride back and forth on the axle causing wobble. If you can get the car to roll absolutely straight with only three wheels touching the floor, that is perfect. Once you get them set, super glue the axles in place under the car and fill the axle groove with epoxy and smooth it flat. You don't want the axles to move--ever.
You will have to add weight for sure. I Use a spade bit to bore out some cavities in the bottom of the car toward the middle. Then I stack 3/4" fender washers with a screw through them and screw them into the cavities. By doing this, you can make minor adjustments to the weight by removing or adding washers during weigh-in. It also puts the weight in the absolute center of the car rather than sticking extra weight on the outside surface somewhere. Make sure that the washers and screw head don't extend beyond the flat bottom of the car. I've also seen people bore holes down the length of the car from the back, fill the bore with BBs and put a screw-in plug in the end of the hole--neat trick.
If your track has a pivotting stop that holds the car in place before the race, taper the front underside of your car back from the horizontal midline of the wood block. When the pivotting stop falls forward, your car will get a fraction of a second head start over cars that have wood below the midline that is in the way of it beginning it's roll. Sometimes that's enough to win a race.
The axle groove closest to the end of the block is the rear one. If you do it the other way, your car will be a little slower.
I saw an episode of Mythbusters where they put golf ball style dimples on the outside of a car and it reduced it's wind resistance considerably. My son's friend who's still in scouts is doing that to his car this year. I can't wait to see if that has any impact.
posted by 64.128.17...
, Tue, 25 Jan 2011 07:17:54, Tue, 25 Jan 2011 07:42:15, Mon, 24 Jan 2011 14:53:55
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