This is one of the most enjoyable things I've ever seen on HN. It's just ... fun.
I remember doing PWD with my dad when I was a kid, shaving #2 pencil cores to get graphite for the axles, making a batmobile one year, and generally doing things that probably had no influence on making the car faster, but that involved a lot of Time In The Shop Experimenting. PWD is the kind of thing that makes hackers out of impressionable youngsters.
"They also didn't have any protection circuitry on them, but I figured that if my car burst into flames halfway down the track, it would totally be worth it."
When I was in Cub Scouts (30 years ago), the rules for Pinewood Derby were (at least as I understood them), fairly strict. You had to use the stock wheels and axles, and carve the car out of the provided block of wood, but you could weight the car any way you liked, up to the specified weight limit.
Given these constraints, there was one optimal design that would always win: essentially, a skateboard about 1cm thick, weighted exactly up to the limit with cast lead, with the bottom of the skateboard waxed. Everyone knew that was the optimal design, but it looked boring, and its performance was completely predictable, so almost no one used it. But every year, there was one kid who (or whose father) cared more about winning than about having a cool PWD car...
I beat you by a fair bit on seniority--going on 50 years. I was the kid whose dad figured out that looks were nothing and weight was all. Somebody who optimized for weight and aerodynamics might have beaten us, but that somebody didn't show up in our troop.
That's interesting, because my first year, I optimized for aerodynamics (and maximized the weight) but lost severely.
In later years, I realized that it had more to do with the wheel friction, and I made cars that were more interesting than perfect teardrop shapes and which also went much faster due to careful attention to wheel placement and lubrication.
I just applied industrial strength lubricant to the wheels/axles and crushed everyone in my troop 3 years in a row or whatever it was. The final year we did it, I didn't even bother carving out or painting the car. I sent the lubricated brick down and it was unstoppable.
I was that kid. To this day I'm still resentful I didn't get to carve my own car with my new Swiss army knife. looking forward to being able to steal my own son's car one day to fulfill my pinewood derby ambitions...
Yes, this. I was in Cub Scouts about the same time (Hey there, old timer!) and can confirm. IIRC the winningest design around my stomping grounds were a pencil-thin body design instead of the flat one you talk about here. And weighed down as much as possible, of course. Absolutely I remember it being boring because of the complete lack of room for experimentation. I did it two years in a row, and being the only experimenter, ended up losing badly both times. Pinewood Derby specifically is the reason I hate sports or games with many artificial limitations that shoehorn every player into a very small number of strategies.
Oh wow, you just made me feel so much better about a decade of resentment. After placing dead last in my only two races, I knew there had to be a way to beat everyone...
My son just joined the boy scouts (or Tiger Cubs or whatever it's called when they're in the 1st grade). I need to review this for... uhmm.. research purposes.
Just a comment, as fun as PWD can be, don't be that parent that clearly did all the work. The purpose is not to make a car NASA would be proud of, but to make the car with your son to end up with a car he made and is proud of.
Usually this results in a car that looks like and reflects the age of the scout (e.g. a Tiger Scout's (Kindergarten) car does not look like a Webelos (5th Grade) car.
Seriously suggest to your pack leadership that they add three races:
-Adult/Sibling
-Adult Scouter
-Adult Vintage
The first give you and your other non-scout kids an opportunity to be a part of things. You can make your NASA approved car that ultimately loses to the simple block of wood that five year old suzie makes.
The second gives the scouts a chance to cheer on their den leaders.
The third let's them see what PWD cars from pack in the day looked like.
Thumbs up to this. My son did a pinewood derby when we were living on the peninsula and many (if not most) of the cars looked like they could only have been made by an adult. Not just like an adult helped, like everything was too polished to be made by a kid of the appropriate age. It just misses the point.
A couple more hints (I have an entire PDF document on speeding up PWD cars).
1) You don't need 4 wheels (except to stay on the track). Lift one of them up slightly so the car is only resting on three wheels. Don't lift the forth wheel up high enough that it's not able to help guide the car along the guide rail.
2) Make sure the car rolls straight. There's a lot of friction against the guide rail if your car is constantly trying to turn into it.
3) Make sure the inside of your wheels are sanded smooth. You want any friction due to contact with the guide rail to be minimized.
4) Put as much weight as possible at the back of your car. Since that weight is higher up the launch hill, it will end up pushing the are longer. Think of it this way: Gravity will stop pulling a front-weighted car when it reaches the roll-out. With a rear weighted car, the back will continue to be pushed when the front wheels are on the roll-out. You get an extra car length worth of gravity.
Many PWD events mandate the use of the stock wheels and axles. The fastest car I ever saw used layers of teflon tubing inside the wheel hub and hypodermic needles for the axles - very smooth bearing surfaces. Beyond the tips above, the most important tip is to eliminate friction in the wheel-to-axle bearing.
I think it's good to have the car not roll perfectly straight, but a little bit to one side. If it rolls too straight, it's going to bump from one side to the other and lose much more energy.
The energy you lose from lateral collisions has very small impact on the forward movement
rolling as straight as possible might bump from side to side, but between the left and right side the wheels will be rotating with as little friction as possible.
deliberately going to one side guarantees that the wheels will never reach max speed.
I paid for the PDF as a guide about 15 years ago and couldn't find a link to the same document. If I remember correctly, these were just four of the twenty-some tips. (We ended up with a second and third place car out of fields of about 80).
My brothers and I we're in the scouts and my dad was a den leader. In pinewood derby season we would design the cars how we want, rasp, sand and paint them until they looked perfect to us, scouts, not parents. When that was done, my dad drill cavity in the car (one year he went through the top of a car into his hand), fill the cavity with molten lead to max weight, then we'd wood putty, sand and touch up the paint. My den had great looking cars and we dominated these races.
That was a lot of fun! A long time ago I designed an electromagnetic "coil gun" for BBs (.177 cal steel balls) as an exercise in electromagnetic fields. While it was mostly worked out in the 19th century it often felt to me like messing with more primitive forces than just charge and magnetic fields.
I remember doing PWD with my dad when I was a kid, shaving #2 pencil cores to get graphite for the axles, making a batmobile one year, and generally doing things that probably had no influence on making the car faster, but that involved a lot of Time In The Shop Experimenting. PWD is the kind of thing that makes hackers out of impressionable youngsters.