Ideas for a mini Pinewood Derby wheel "lathe"

The BSA sells an arbor (or did ~14 years ago when my son raced) that you can mount wheels to. It's like the arbors Dremel sells for cut-off wheels. You may be able to mount it in a drill motor and run it at high speed, creep up on a block of sandpaper. Don't know if the rules have changed or not, but back in the day reshaping the wheels was not allowed, only truing them up.

Pinewood derby racing is basically an exercise in the elimination of friction. The maximum possible speed can be calculated by converting potential energy ( mass x gravitational constant x height) into kinetic energy ( 0.5 times mass times (velocity ^ 2)). Mass cancels out (like Galileo dropping 2 cannonballs of different weight which hit the ground at the same time), so the formula boils down to "Velocity = Sqrt ( 2 X 32.2 ft/sec^2 X height)". A track with a 5 foot tall starting block has a maximum theoretical speed of 17.94 ft/sec or 12.23 mph.

Our son won a lot of races following the rules. We also ran an open race that we won multiple times (no rules). Typical "within the rules" tricks are to work the nails near the head and polish them. They had flash near the head which could be needle filed off, then polished. We trued up wheels on the lathe with the BSA arbor. Then ran the nails with wheels mounted in a drill chuck up to speed and added graphite. Once the graphite was worked in, we spun them up to speed in the drill motor, released the drill motor trigger and timed how long that particular wheel/nail spun until it stopped. We'd get wheels that would spin for anywhere from 20 seconds to about 75 seconds. Naturally, the 75 second wheels/nails went on our son's car.

Another "trick" is to adjust the camber on one of the wheels so it isn't touching the ground. Idea is there's less rolling resistance with 3 wheels touching instead of 4. Also camber the tires so just the edge is touching.

Another one is to carefully push the car on a flat surface (we used the school's gymnasium) and see how straight the car runs. Turn the nails and/or put a little pressure forward/backward to true the steering. Hitting the track bumpers equals friction.

Yet another "legal" trick is to bias the weight to the rear of the car. We biased our son's cars to about 4.5 oz. on the back wheels and 0.5 oz. on the front. The idea was to move the center of mass as far back as possible on the car. When the car is in the starting blocks, the center of mass will be higher than if in the middle, so it's effectively at a higher height than a car with the weight at the front.

For the "open race", we machined the wheels to a knife edge for less rolling resistance. We also used thrust bearings on either side of the wheels. Also put a rare earth magnet in the front of the car. Our starting block was a pivoting dowel with 16D nails sticking up as stops. Our "open" cars were literally thrown down the track at the start; the cars stuck to the nail and when the dowel was spun it gave the cars a good pull for a push start. Totally "legal" in an open race; sure perplexed a lot of dads when they'd see our cars win by large margins.

We never lost a heat on the open races, think my son's cars lost one or two heats but ended up the overall winner every time. Great fun to work with "the boy"!

Thanks for posting and bringing back old memories!

Bruce

Only if I knew half of this back when I was in Cub Scouts!!! I did polish up the nails on dad's 9" SBL along with the wheels, but I never did win any races. Not even close! It was tough back then, some of the kids we competed with their dads worked for NASA in Clear Lake. At the time we lived on the south side of Houston. Good old days!
 
And all these years, I thought it was supposed to be a competition for the kids.

I don't think the playing field has ever been level. Kids who have dads that are builders have an advantage, even if they do all the work themselves as they've been exposed to building techniques and tools. Some kids (like me) didn't have a dad as mine died when I was 4.
 
i made my pinewood cars with my father over 30 years ago, boy they were crude.
we used a jig saw, hand saw, wood chisels, sandpaper, and the supplied pinewood kit to create 2 mediocre cars back to back events.
one year was a basic wedge design, the second year was more like an 1900's indy 500 race car (i just thought those old indy cars were cool)
the only thing out of the ordinary done to either was the use of powdered graphite on the wheel bores and the axle before assembly

i wish i would have considered drag coefficient or magnetic propulsion, or if the dang things would even track straight :oops:
the fun was in the build and spending time with my dad, i'm thankful for that- winning the race was not considered when we were making them
 
We had a air compressor pump, an old refrigeration pump, made into a air compressor less the tank. Dad would take the pulley off the motor, which was a old washing machine motor, and mount a wooden drum on the motor. On that wooden drum we would glue emery cloth to the drum with contact cement. That is what we used to sand down the body of the derby car with. Worked quite well.
 
Vitamink,
The motor stand and wheel lathe is this something you built or did you purchase them?
Dana
 
Dear Vitamink,
After re reading your post it looks like the picture you posted is a homemade slot car wheel lathe. Is there a chance you would be willing to share with me the plans of this homemade version? It would be greatly appreciated. Thanks Dana
 
Dear Vitamink,
Could you help me build the lathe that you posted? I would like to use it to lathe roller blade wheels. It would be greatly appreciated.
Thanks, Val
 
I would like to build a car where one of the wheels is a brushless DC motor. Hide the batteries deep in the wood body. Name the car "Lance."
R
 
I am sitting here wondering if there would be a way to bore a true hole in the center of the plastic wheels, and run a needle bearing that is small enough to fit under the lip of the nail holding it all in?
 
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