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Lorentz forces and cheating at the Pinewood Derby
- strictnein 11y agoMy 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.
- rubidium 11y agoNot to ruin the story, but he placed 4th out of 4. You'd be better off spending time on getting your tires perfect and figuring out which lane is fastest :)
- peejaybee 11y agoThe latter won't matter if they do as my pack did, where each race had three heats and each car raced in all three lanes. But yeah, get your wheels right and polish the heck out of your axles.
- smoyer 11y agoA 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. Good luck!
- emerongi 11y agoI 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.
- smoyer 11y agoHave you done A/B testing on that? I'm genuinely curious about which would win.
- ezl 11y agoThe 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.
- krisneuharth 11y agoLink?
- smoyer 11y agoI 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).
- CIPHERSTONE 11y agoJust 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. Just some suggestions from an old Cubmaster.
- strictnein 11y agoOh, I won't be, my comment was mostly tongue-in-cheek and also remembering how my the creations of my father and I never did that well. 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...
- CIPHERSTONE 11y agoIt's really a blast to see the old cars, and the adult race is fun because then you can see some really great adult designs.
- georgeecollins 11y agoThumbs 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.
- jaredhansen 11y agoThis 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.
- te_platt 11y agoFrom the article: "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!
- ChuckMcM 11y agoThat 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.
- dyladan 11y agogoogle cache http://webcache.googleusercontent.com/search?q=cache:k-OXSfSOTWYJ:ch00ftech.com/2015/10/12/lorentz-forces-and-cheating-at-the-pinewood-derby/&hl=en&gl=us&strip=1&vwsrc=0 http://webcache.googleusercontent.com/search?q=cache:k-OXSfS...
- NoGravitas 11y agoWhen 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...
- karmajunkie 11y agoI 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...
- mwcremer 11y agohttp://www.imdb.com/title/tt0398971/ http://www.imdb.com/title/tt0398971/
- karmajunkie 11y agoI can't wait to watch this :)
- dluan 11y agoOh 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...
- cafard 11y agoI 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.
- matthuggins 11y agoMirror? The site is down.
- craigmcnamara 11y agoMy 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.
- deleted 11y ago[deleted]
- panglott 11y agoThe simpler explanation is that the VW Diesel that won was cheating the system too ;)
- deleted 11y ago[deleted]
- elwell 11y agoI still remember winning "Best of Show" when I was a Tiger Cub. Took me a couple decades to realize this was a booby-prize.
- hinkley 11y agoI suspect the real reason you lost is due to the aluminum track rails and eddy currents. You'd need a way to switch the thing off almost immediately.