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September 14, 2004

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Ah, the Pinewood Derby. I competed in several of those when I was younger, and am ever so slightly scarred by the experience to this very day. I'm the eldest child in my family, and so when the pinewood derby came around my father and I, in our naivete, set out to build a car.

Specifically, to have me build a car. I couldn't have been more than eight or nine, and with the only help from my dad coming in him pointing me in the direction of the workbench, and his making sure I kept all my fingers, my first attempt turned out something remarkably similar to that charred hulk you linked to above.

Needless to say, it didn't win any races. I remember it having a particularly poorly done yellow paint-job, complete with black racing stripes, painted by my unsteady hand. Ah, memories.

The next year, we bowed to the inevitable, and dad helped me build the car. I was, however, determined not to build one of the typical winning vehicles, (shaved down to be as nearly flat as possible, then loaded up with melted lead fishing sinkers to get them up to the (I think) 5 oz. limit. ) so my car looked like a cross between a fish and a comet. It didn't win either.

In fact, in my entire career in scouts, I never won a pinewood derby race. Which I now think is quite funny, especially considering the fact that the team of my younger brother and my father won first place every year they entered!

They did it by shaving that block of wood down as much as they could, sharp at the front, and just thick enough to fill the bottom with metal and leave enough wood to support the nail/axle arrangement. Liberal doses of powdered graphite were applied to the nails to serve as lubrication. I believe they would take the wheels off and re-lubricate between races, though I'm not certain of this.

That's old technology, though, in terms of the pinewood derby. 15 years at least, so it may be severely outmoded now. YMMV, but good luck!

crutan

This guy has some decent observations. Check it out. He talks about lubrication, aerodynamics and weighting.

Summary: put the weight high, don't worry about aerodynamics (velocity is fairly low for laminar flow concerns), and use graphite lube for the axles.

I really don't know if this is good advice, but I do know that designing a pinewood derby racer is, as far as aerodynamics is concerned, nothing like designing an airplane. Important concerns are going to be minimizing static and dynamic friction between solid surfaces, most likely.

Curtan and Slarti,

thanks for the advice...excellent site, Slarti!

Yeah, I lost every one of these I raced as a child, too. I still have an adverse reaction to the plum purple enamel color I used to paint the car I was SURE was going to win one year...

"axles"? are you sure? That just looks wrong...is "axel" possibly an alternative spelling?

"Put the weight high"...does that mean on top of the car or near the back of the car?

Axel is a figure-skating move, Edward.

Axel is a figure-skating move, Edward.

Ahhh...my secret is out...I'm actually Brian Boitano.

Ya know, where I grew up, it wasn't a good design if there wasn't enough wood available to bore out and add an Estes rocket engine once that year's race was complete...

"Axel" is a figure skating term, and it takes its name from Axel Paulsen, and not axle. Spelling of this word can be confusing because of axis/axes, which shares the root (I think; I'm certainly no linguist).

way ahead of you there crionna...already picked out an abandoned parking lot ;-)

Dang. Well, I was composing at the time...

Which is altogether better than the opposite, truth be told.

Edward -- we didn't have these when I was a kid. (Not that anyone ever told me about, at any rate.) We did, however, have go-cart races, where 'go-carts', for our purposes, meant whatever we could make out of whatever materials we could find, without help from our (unmechanical) parents, that rolled. As I recall, I usually won, having managed to snag a baby carriage, while my little sister had to make do with something with wooden wheels attached to a board with very thick nails. The big problem was that while I had wheels and brakes, my cart wouldn't turn; hers had "wheels" and steering, but no brakes. Fortunately for my racing career, none of the sloping driveways that were our racecourses required turns.

hilzoy,

without help from our (unmechanical) parents

First time I read that, I thought it meant you were trying to reassure us your parents aren't robots. ;-)

brakes vs. steering...tough call. Kind of like bonds vs. stocks. All depends on the road ahead, eh?

Kind of OT, but I did really like the "Pierogi Joe" comics on the gallery's website.

crionna - I haven't thought about Estes rocket engines in twenty years. Damn, those things were great. Well, I've got my first kid on the way, so I hope he/she is an utter geek so I can do all of that stuff again...

Kind of OT, but I did really like the "Pierogi Joe" comics on the gallery's website.

Yeah, they're great...it's a great gallery.

Wheels have to be secure and perpendicular to floor. The axle should be buffed smooth and graphite added. The contact between the axles and the wheels should be the only points of friction and that friction needs to minimal. I always figured the weight should be centered - I don't know why making it high would make a difference.

My best attempt was basically a rocket shape. It was a small cylinder with lead poured into the entire length of it. It had a pointed tip in front with a fin in back. Wings reached out to meet the wheels. I painted it silver so it was reminiscent of the X-1 that Check Yeager flew to break the sound barrier. OK, maybe that's not the first thing you'ld think of but I liked it. By the third race one of the wheels was coming off. Lesson #1: Secure and perpendicular wheels are most important thing!

In my only other venture into Pinewood Derby I sculpted a pickup truck. Maybe that's unimaginative but nobody else had one. It was a big hit - all the kids liked it. It ran a very slow race and one of the wheels fell off. Lesson #2: Secure and perpendicular wheels are the most important thing!

Secure and perpendicular wheels are the most important thing!

I may have a problem with that, given that the wheels have to be exactly 1 3/4 inch apart and I carved the tube shape such that there's not much for the nails to sink into at the one end of the piece...I may need longer nails, I guess.

And nailing into a sculpted piece so that the wheels are perpendicular, without destroying the paint finish is also giving me a headache...you need an entire workshop to do these things...

Quoted without comment:

I still have an adverse reaction to the plum purple enamel color I used to paint the car...

Ahhh...my secret is out...I'm actually Brian Boitano.

;)

st: crionna - I haven't thought about Estes rocket engines in twenty years. Damn, those things were great.

For me, the mere mention of model rocketry instantly evokes that distinct gunpowder smell.

I'm with Slarti's original recommendation. The race is too short to really worry about aerodynamics having much affect. Obviously within reason.
Pencil lead (graphite) probably works better than silicone.

Find a block of wood with parallel sides and use it as your spacer. Then place your axles on both sides of the block and glue them to your racer's underside. Do not glue the spacer.
When dry, remove the spacer and your axles should be parallel.

When dry, remove the spacer and your axles should be parallel.

Excellent suggestion, carsick. Thanks!

Although, I have to admit to being a bit hesitant to take advice from soemeone with your handle about this.

;-)

My handle was created as a metaphor for how I feel on the current administration's "trip".

My handle was created as a metaphor for how I feel on the current administration's "trip".

got it...

thanks for the info again...I think it will work perfectly.

edward, you're in trouble.

I believe axels are only lubricated by water temporarily melted under the pressure of an ice skate edge.

For me, the mere mention of model rocketry instantly evokes that distinct gunpowder smell.

Mmmm, gunpowder. Off to the range!

Since we're already into spot-the-misused-homonym territory: carsick, does aerodynamics ever have an affect?

hilzoy
I'm not sure what you mean. Do cars fly? no. Do they move through air? yes.
Or are you referring to "affect" as opposed to "effect"?
I may be wrong there but:
affect
n : the conscious subjective aspect of feeling or emotion
v 1: have an effect upon; "Will the new rules affect me?" [syn:
impact, bear upon, bear on, touch on, touch]
2: act physically on; have an effect upon

number two comes close.

Your credentials shine through hilzoy.
"The confusion of the verbs affect and effect not only is quite common but has a long history. The verb effect was used in place of affect (1, above) as early as 1494 and in place of affect (2, above) as early as 1652. If you think you want to use the verb effect but are not certain, check the definitions here. The noun affect is sometimes mistakenly used for the noun effect. Except when your topic is psychology, you will seldom need the noun affect."

In which case...it was a typo. Yeah, that's the ticket. My finger didn't make it up to the "e" and mistakenly hit the "a". (Of course I never use preview because it erases my personal info.) So any time you see a "their" for "they're", be forewarned, it's also a typo.

Forward or rear, I think, is not as important as higher or lower. My only three bits of advice: router, birdshot, silicone.

Go Team Colgate.

For those interested in lots of speed tips and other goodies for pinewood derby cars check out http://www.maximumvelocity.com . No I'm not affiliated with them, I have ordered some supplies from them though.

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