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Make a Winning Pinewood Derby Car
Getting you into the top 2%
When I say you can make a winning car, I mean "get yourself into the top 2% of contestants." This hub does not guarantee you'll win, but following this advice will dramatically increase your chances.
A word about who competes:
Some say a pinewood derby is a competition between fathers, and not the scouts. I think the more correct answer is: A pinewood derby is a chance to get father and son together (or mother and son, or mother and daughter; girls can participate, too). A scout activity that includes a parent is, in my opinion, inspired by God, because beautiful things happen when a parent participates in significant projects with his/her child. Spending time with his/her father or mother is highly important in the mind of a child. Among other things, the two can bond very easily. Planning together, sharing a discovery, achieving a project together, hoping for each other's success, suffering together, winning together OR losing together makes up the spiritual magic found between two people.
One more word of caution:
Don't tell your child that he's sure to win, even if the odds look real good. This could result in two things: He will tell his friends he's got something up his sleeve, which may result in negative rivalry, and he will get his hopes up too high. In a competition with peers, losing after being promised success can be devastating. Just let the discovery of winning come as a very pleasant surprise. If he loses, which is always possible no matter what appearances are, then the disappointment won't be so severe.
On to the block of pine that will become your treasured relic:
After you have been issued the kit which includes the pine block, the wheels, axle pins and whatever else, find out immediately the weight limit on the finished car. Next, find some lead. You can buy lead shot at a gun shop, or ask a tire store mechanic how you can find some. The lead I've used has been extra or left-over, and I've paid nothing for it. At home, weigh the kit and the lead together, until it measures a few grams over the limit. You want to do this, because the pine block will reduce in weight as you form the body of the car. At the derby the judges will weigh each car, and will drill out some of the lead if it's over. You can do that, too, at home with a gram weight scale and your own drill.
Next, create grooves on the inside hub of the wheels, if it's not illegal. A machinist may do this for free or cheap, or perhaps you can do it to some degree by inserting a hot screw and forcing it into the hub without damaging the plastic. Make sure the heat doesn't melt the plastic to the point of creating beads inside the hub. If that happens, you can smooth them down with a piece of pipe-cleaner covered with a fine abrasive paste, such as the type that comes in the Diamond Finishing Kit, whose ad is attached to this article (also see video below). See the illustration below to get an idea of what the grooves might look like. The purpose of these grooves is to help retain the graphite lubricant inside the wheel hubs. Usually contestants are permitted to apply the lubricant just before the race, but not again until the race is over. These grooves will help retain the graphite for a much longer time. Also, the grooves mean there is less rubbing area on the axle, which means less friction. The difference may seem to be negligible, but anything you can do to increase the speed will be worth it. I say that, based on experience: My son's car clocked in at the exact time, in milliseconds, as another car. Even though both showed the same reading on the panels, the electronic system determined that the other car won. It isn't known what mechanism was in place to give the credit to the other car, but I imagine that even a millisecond of difference would have made a more sure determination.
I recommend that you use graphite as the lubricant. It's a proven agent. I once tried powdered teflon. The hobby store owner assured me it was better than graphite. I bought the teflon, thinking I had my "secret weapon." At the races, the car had a very nice start, but you could see it decelerate noticeably after leveling out. It's performance at another race after using graphite was greatly improved. My rule of thumb in using revolutionary and "secret" means or methods is: Don't seek too much of an advantage over others, especially if you have to keep it secret, and especially if it hasn't been tested. Give the others a fighting chance. Your extra knowledge of physics and what you'll learn here will be good enough to have a good time. One acquaintance that won over my cars had freely given me advice beforehand. Had I told him about using teflon, it would have saved my son less disappointment, because he told me later he knew it doesn't work. Don't be afraid to talk about your ideas, your secrets, and this advice I'm giving you. This results in comradery, good will, and -- very importantly -- corrective advice.
Now, it's time to form the car. In doing this, cut out a slant or curve from the bottom front and bottom back edges of the block. On the racetrack, there will be a raised guide ridge between the wheels, and if the front or back edge of the car comes in contact with that ridge while the car is bouncing, it could slow it down. In addition to this cut-away, the front end should have a higher cut-away, in case the retainer gate is pulled away downward. In all likelihood, this will not influence the starting time of your car, but in case it is moved away slowly, your car is already ahead of the one whose front "bumper" is lower. See the above diagram for this demonstration.
Make your car short (vertically) at the front, and thicker toward the back. This will reduce wind resistance, and place more weight at the back of the car. The reason you want more weight at the back is explained in the next paragraph.
Next, make a square notch in the bottom of your car -- a place where you can put the lead. You can either screw the lead into the hole, or melt the lead and pour it in. What I do is to put a small screw in the middle of the hole, screwing it in until the head of the screw is within the bottom edge of the car. Next, I melt the lead with my butane torch (these can be bought at a sports store or from the sports isle of a superstore). The lead is then poured into the hole, flooding around the screw. The screw helps to hold the lead in place very securely. Be sure to use all the lead that was weighed with the kit. You can remove the excess later, if needed. When you make the hole for the lead, put it toward the back, near and in front of the rear axle slot. Here is why you want the weight to be as far back as possible: If your car is racing another one who has their weight toward the front, and if the two cars are exactly in the same position on the slanted ramp, gravity is working harder on your car, because the weight is still higher (further away from the center of the earth) than in the other one. This gives your car added impetus while it is still on the downward slant. Make sure the screw or the lead does not poke down beyond the bottom edge of the car; these could rub on the guide ridge and slow down the car.
Next, make the nose of your car pointing outward. The detection laser is placed at the center of the track. If you make "headlights" on your car that stick out in front of the hood, then the laser will miss these, and it could mean the difference between winning and losing. If you have these headlights, the detention gate at the top of the track will probably keep the nose of your car further back than those who have a longer proboscis.
Finally, work on the wheels. After you place them, Glue the axle pins in with a strong welding glue. When the glue is completely dry, test the car on the kitchen floor. As it rolls away from you, check which direction it turns. Roll the car from North to South, from South to North, and from the East-West directions. Do this several times until you're sure the car has a preferred direction it travels. Now, with needle-nose pliers or grabbing carefully the wheel with your fingers, bend the front axle pins in a way that will correct this wayward motion. You won't have to bend the pins much. Keep tweaking until the car moves in a straighter course. This will help it to not come in contact with the center guide ridge so much, which slows it down each time that happens.
A kit for great results:
Some places may prohibit the machining of the treads of the wheels. If not, you may want to turn the flat tread into a pointed tread - or even a hollowed-out tread - thus reducing friction and bumps on the track bed. Also, reduce friction by filing down the part of the hub that touches the side of the derby, as shown in the video that follows. Also, if the axle nails are not polished, the video shows how to smooth out the axles.
What the car looks like and it's color or shine factor is up to you. There will probably be awards based on creativity or looks, so it won't hurt to spend some time in that area. Home Depot or Lowe's can show you how to get a super metallic type shine or finish on your car, and there are wonders in hobby-store decals as well. I helped my son to put a fin on his car, which was just carved out of the wood. Pine is good for doing that sort of thing. That car was the one blessed with teflon, but it won best design because of the fin in the center.
Well, you're all set to go! Follow these steps and watch the excitement grow in your child as his car competes. If it doesn't win, it'll sure be a worthy opponent!