Lorentz forces and cheating at the Pinewood Derby
ch00ftech.com
ch00ftech.com
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."
That's the spirit!
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...
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.
You'd be better off spending time on getting your tires perfect and figuring out which lane is fastest :)
But yeah, get your wheels right and polish the heck out of your axles.
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.
Good luck!
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.
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.
Just some suggestions from an old Cubmaster.
Obviously you have to help a 6 or 7 year old to a degree, but I plan to be as hands-off as possible, when the time comes.
I like your idea of multiple races. I'll have to go and find my old PWD cars. They're somewhere...