Several years back, I found a fantastic site on cub cars. Can't tell you where it is now, though.
It talked about lubrication (matters lots) , aerodynamics (doesn't matter!) , weight and where to place it (as much at the back as possible and maximize to the legal limit - get it weighted at the post office to be sure...), how to make the wheel pins smooth and minimize friction, etc. Even said to build it so one wheel wouldn't touch the track, but I think that's illegal in the Cub car world.
I'm sure a Dags on "pinewood derby" will pull up quite a bit of info. I was one of the ones (many moons ago) that sort of made my own (well dad cut the body on the bandsaw) - but I did the rest.
Sadly, I think I was probably the only one - and my position in the finals were evidently testimony, probably, not to the "skills" of the other young builders, but, rather, their fathers as I didn't do research on lubricants and other such things.
Maximum weight 5.0 oz (FYI: heavier cars do better) Wheel spacing can't change under-car clearance minimum (i.e. don't add things underneath) Can't extend beyond wheels sideways some tracks have a height max too. Must be at least partly built by the scout. length maximum too
Each pack chooses which of the official rules they'll follow, but there is a common set of rules most follow, which should be easy to find now that you know what to google for.
Oh - tip for the little ones. Disk sander. In our house, that's the tool of choice (and usually the scroll saw for roughing) for pinewood derby car carving. Once you get your kit, make a few extra wooden blanks for them to experiment with (save the official blank for the official car).
Adding weights: forstner bit into the bottom, use a flat head screw to attach washers. Easy to adjust this way. Or you could do what my daughter did, and build a truck - and fill the bed with big hex nuts :-)
As a metrologist (calibration and standards) at my place of employement I can always tell when the pinewood derby time rolls around. I have a steady stream of Dad's weighing cars, wheels, lead shot etc on some of my really accurate high resolution scales. 4.999999 oz. anyone? Mike in Arkansas who may exeragerate slightly the resolution of his scales.
Actually, our official race scale is only precise to 1/10 oz, so 5.049 oz would be the max for our race. Depending on the accuracy of the scale, of course.
Our pack also has a Polar Derby. Each den builds a sled, one cub rides inside, one on the back skids, and the rest of the den pulls. Through the woods at my house, no less :-)
My son and I made a match box car (20 years ago ;-)) that came in third in his pack. As I recall, the scout pack provided the car shaped, wood blank. We rough cut the blank then sanded the corners and finally painted the car a bright red (red cars always go faster!). The weight of the car, I am told, is the biggest impact on speed because the car track is gravity feed. I mortised a notch in the bottom of the car and we glued in pennies, as necessary, to reach the 5 oz maximum. The glued pennies did not extend beyond the mortise so the bottom of the car could not catch on anything on the track. The local Post Office was the official weight in station for the race. We used powdered graphite (like you use on door locks) to lubricate the wheel axels. The Pinewood Derby car race was a lot of fun and a good father-son project. Good luck!
I was always in charge of building the car, but dad did the weighting. We used melted wheel wieghts where ever we could put them. But I remember dad's rule of alway bring a drill and bit to the derby just in case it needs to be lighter. (Note, those where the days before battery powered drills and EPA rules against melting lead and a whole bunch of other things we did, hahahaha.)
I had two top three finishes out of three years. (The third year I made a three wheeled trike. Took the prize for design, but wouldn't run straiht on the track. I figured that going it, but I digress.) Looking back, I think a lot of my sucess was due to wheel alignment. We had seperate wood axels with nail spindals. I think the designs are different now, but dad always had me align the axels with calipers. I didn't really appresiate why it mattered then, but I suspect now that wheel alignment cut down on alot of friction as the car rolled down the track.
#1 make a car that jr will be proud of hanging on his wall, win or lose (and make sure he helps)...we have more than a few pieces of art (and all my fingers are still attached) and actually have more than a few trophies as well...a few years after the fact, former is much more important to the boys than the latter. Shape and finish are a pleasure to goof with. #2 watch the design...track has some nasty angles on the decline that will hurt bad if the car wants to nose-dive. A thin strip of wood is applied to the track to keep you honest on the width between wheels. #3 is play by the rules and learn the rules each step of the way...our last car (a beauty in its own right) cruised through local and regional play, only to be disqualified at the top due to some technicality about the wheels
1) Buy a kit.
2) Let the kid design it (and build as much of it as is reasonable) It doesn't matter how silly it looks if the kid is happy with it.
3) Don't worry about winning; you won't unless you cheat. Even then, it is not a sure thing because luck is a big factor. (and a bunch of other guys are also cheating)
I agree with others that the secret is in the wheels. They need to be accurately aligned. Test it on the floor to see that it runs straight. Moreover, the car needs to be accurately placed on the track so that it starts straight. Don't let anybody else handle the car that might disturb the wheels. The nails that they used to supply for axels were very poor. It could be improved by chucking it in the drill press and smoothing with a file folled by fine emery.
I made one demonstration car with special wheels. I bored out the standard wheel and glued a glass bead in the center. Then I made an axle of a hat pin. The polished steel on glass was very frictionless.
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