Pinewood Derby advice?

[Sully]

My girl is in Girl Scouts, and we are heading so to a build day to work on her car. I never got too into it the one time I did it when I was young, but I find myself acting like Clark Griswold on this... So any advice (other than back away, and stop making this about me!)?

Rules:
Has to run on all 4 wheels
No beveled axles (I don't know if this means I can bend it or not).


I bought a wedge car. Plan to put weights 1.25" in front of the rear axle. Graphite lube.

What else do I need?

[Fishpicker]

i used to make those with nothing but a dremel, sand paper, and paint.

my fastest car was modeled after Optimus Prime, a flat nose semi. I think it performed better than the other cars because a lot of the weight was in the front half of the car.

here's everything you need to know about axles (http://www.maximum-velocity.com/axlesqa.htm)

[bobbymitch]

Pinewood Derby in Girl Scouts? Good for them.

Polish the axles. Chuck them in a variable speed drill, use 1200 grit sand paper/emery cloth and get them smooth. Powdered graphite is good

Hopefully you have a good scale to bring the car right up to the max weight allowed.

Bury the weight in the bottom of the car.

[kc rush]

Here you go


http://youtu.be/a5A6SCE0eVw

[Buehler445]

A lot of efficiency is lost if the wheels move laterally while it's going down the hill.

[Chromatic]

Here you go. My dad helped me with mine as a kid and we always won. It was sleek but with a heavy rear for the flat part of the track.

<iframe width="560" height="315" src="//www.youtube.com/embed/-RjJtO51ykY" frameborder="0" allowfullscreen></iframe>

Edit: Fuck, beaten.

[TLO]

Watch the South Park Pinewood Derby episode and all will become clear.

[RealSNR]

Fuck trying to win the thing. My dad just tried to make sure I had the coolest-looking car.

He did an exact replica of a Chevy Suburban. Man, that thing was badass. He had to hollow out the bottom because he needed an entire extra block of wood added in order to get the right dimensions.

And I actually won a couple of my first races.

[sfchief]

"turn" or just sand the axels smooth and use graphite on them

[wazu]

Make sure that the wheels all spin completely free. When you push it across a wood floor it should stay straight, not veer to one side. I don't think aerodynamic matters significantly. Seems like our least aerodynamic cars win more for some crazy reason. That's about all I've got.

[mlyonsd]

"turn" or just sand the axels smooth and use graphite on them
This, plus we hooked the cars up to a treadmill and ran them for a several miles, stopping periodically to re-graphite them.

[MahiMike]

Secret is to use graphite on the axles. I won mine once with that stuff. The guy launching my car had black hands.

[007]

angle the axle just slightly so you have only the edge of the wheel touching instead of the entire wheel. Less friction.

[Eleazar]

My dad drilled holes in the bottom of mine and sunk screws in it everywhere to increase weight, and we put that graphite lube stuff on the axles. But the main thing is reducing friction to the wheels.

[wazu]

My dad drilled holes in the bottom of mine and sunk screws in it everywhere to increase weight, and we put that graphite lube stuff on the axles. But the main thing is reducing friction to the wheels.

They have stick-on weights now that are much better. By the way, I should mention that you need to start by going to Hobby Lobby and raiding the Pinewood Derby section.

[MTG#10]

When I was a kid I drilled a hole in the rear end and stuck lead fishing sinkers in it to add weight then sealed the hole with a little play doh to keep them in. That's all I got. :shrug:

[eDave]

What is the weight limit? Heavier, to a point, is better. Also, graphite on the axles, specifically at the wheels.

Zoom!

EDIT: It appears I have Q'd.

[Dave Lane]

Here you go


http://youtu.be/a5A6SCE0eVw

Great link!

[eDave]

When I was a kid I drilled a hole in the rear end and stuck lead fishing sinkers in it to add weight then sealed the hole with a little play doh to keep them in. That's all I got. :shrug:

I balanced the weight out. But just a little more at the front. Felt like it 'pulled' the car down the slope better.

[Dunerdr]

Personal trick was nailed in wheels make one sight slightly higher so it only rolls with resistance from 3 wheels.

If the track is a varying slope track use liquid for weight. I used mercury. When the car goes over the edge the weight rushes forward creating more momentum.

Use the glossiest paint possible for the least air resistance.

Make the car a wedge obviously for better arrow dynamics.

Also if your doing a wedge keep the angle as tight as possible and use your entire length of the wood block.

Make sure your alignment is dead on.

Pinewood derbys the only part of scouts we were serious about as a kid. I had two identical wedge cars. One for our scout troops straight plywood track with solid lead weight.
Then the twin car with mercury for more inertia at the regional and state tracks.

Edit: just talked to my pops angle the wheels on a lathe or sand them so only the inner edge touches. And clean the inside of your hub. And smooth the inside runner part of your wheel.

[kccrow]

1st, follow the rules of the association. I'm sure they follow the same rules as the BSA, which are very specific on the degree you can bend axles, modifications to wheels, dimensions of the car, etc.

3/8" clearance on the track, at least 1/2" front nose width, no greater than 3" height at any point, no greater than 15 degree axel angle, very limited on wheel modification (mostly only enough to ensure they are actually round)...

A wedge works well for aerodynamics... Try to make some kind of spoiler/lip at the rear.. subtle like a corvette rearend... with weight to rear.. place added weight right at center of gravity which you want to try to get as close to the rear axle as possible and most try for 3/4" or less. make the car forward of cog and behind front wheels as narrow as allowed (kind of like a indy car) and I think that has to be 1-3/4". If they let you completely remove some material from this section, do it. get tungsten cylinders for weights and drill through side of body to insert at precise cog location.

[Sully]

So the build day was a cool setup, with some awesome volunteers.
Had a few tables set up for design.
Had three guys manning jigsaws ready to cut what you needed.
Had 3-4 volunteers with dremels to polish the axles.
Had a table with a bunch of sandpaper out.

Now I just need to find a way to weigh it properly. May have to buy a scale.


And yes, there is a huge portion who is just concerned with having the cutest car. My daughter will probably be in that group as she goes forward, but today was just fascinated with the process.

[Sully]

1st, follow the rules of the association. I'm sure they follow the same rules as the BSA, which are very specific on the degree you can bend axles, modifications to wheels, dimensions of the car, etc.

3/8" clearance on the track, at least 1/2" front nose width, no greater than 3" height at any point, no greater than 15 degree axel angle, very limited on wheel modification (mostly only enough to ensure they are actually round)...

A wedge works well for aerodynamics... Try to make some kind of spoiler/lip at the rear with weight to rear.. place added weight right at center of gravity which you want to try to get as close to the rear axle as possible and most try for 3/4" or less. make the car forward of cog and behind front wheels as narrow as allowed (kind of like a indy car) and I think that has to be 1-3/4". If they let you completely remove some material from this section, do it. get tungsten cylinders for weights and drill through side of body to insert at precise cog location.

I got tungsten putty. Only got an ounce, though. May need more.

[Baby Lee]

Here you go


http://youtu.be/a5A6SCE0eVw

A little more discussion to be found here

http://gizmodo.com/the-science-behind-making-the-fastest-possible-pinewood-1563716398

[eDave]

So the build day was a cool setup, with some awesome volunteers.
Had a few tables set up for design.
Had three guys manning jigsaws ready to cut what you needed.
Had 3-4 volunteers with dremels to polish the axles.
Had a table with a bunch of sandpaper out.

Now I just need to find a way to weigh it properly. May have to buy a scale.


And yes, there is a huge portion who is just concerned with having the cutest car. My daughter will probably be in that group as she goes forward, but today was just fascinated with the process.

That's interesting. Back in my day, you just bought the kit and did it all at home, then showed up for race day. Kids these days... Probably working that shit out in Auto-Cad.

[Sully]

Funny thing was, my daughter found a shape she wanted her wedged saw into. I couldn't bring her to all this and tell her no, so we traced out the shape.
Stood in line, kept looking at it, didn't look straight, go back and retrace.
Stand in line
Still not perfect
Retrace.


I swear to God I probably retraced that thing 6 times, trying to make it perfect.

All my daughter cares about is if we can paint it like a cheetah...

[eDave]

Funny thing was, my daughter found a shape she wanted her wedged saw into. I couldn't bring her to all this and tell her no, so we traced out the shape.
Stood in line, kept looking at it, didn't look straight, go back and retrace.
Stand in line
Still not perfect
Retrace.


I swear to God I probably retraced that thing 6 times, trying to make it perfect.

All my daughter cares about is if we can paint it like a cheetah...

You should have had a boy. Next time, doggie style gets you a boy.

[Dunerdr]

You should have had a boy. Next time, doggie style gets you a boy.

Wich one gets you a girl? I have a boy. Wife wants a girl.

[listopencil]

Pinewood Derby in Girl Scouts? Good for them.

Polish the axles. Chuck them in a variable speed drill, use 1200 grit sand paper/emery cloth and get them smooth. Powdered graphite is good

Hopefully you have a good scale to bring the car right up to the max weight allowed.

Bury the weight in the bottom of the car.

^This.

Make sure to buy a tube of powdered graphite. Unless the rules have changed, that's the only "lubrication" you can use on the axles. Go buy some lead fishing weights from the hardware store and get access to a very accurate scale that will measure down to 10ths (or even 100ths) of an ounce.

[listopencil]

Oh and lightly sand the wheels to remover any irregularities.

[Sully]

^This.

Make sure to buy a tube of powdered graphite. Unless the rules have changed, that's the only "lubrication" you can use on the axles. Go buy some lead fishing weights from the hardware store and get access to a very accurate scale that will measure down to 10ths (or even 100ths) of an ounce.

I've got the powdered graphite.

[Sully]

I am a teacher, so I'm gonna try and see if there are any science teachers that might be able to help me out with a scale.

[eDave]

Wich one gets you a girl? I have a boy. Wife wants a girl.

Gonna have to ask Sully.

Just yankin your chain Sully.

[Sully]

Gonna have to ask Sully.

Just yankin your chain Sully.

It's been 7 years and a few weeks since that particular session. I'm guessing it has something to do with begging, quick work and shame.

[eDave]

:hump:Wich one gets you a girl? I have a boy. Wife wants a girl.

In all seriousness, to conceive a boy, deep penetration is key, but for a girl, the opposite is true. Having sex in the missionary position is said to increase your chance of conceiving a girl, because it limits the depth of penetration. This in turn, restricts how close to the cervix, the sperm are ejaculated. Boy sperm swim very fast for short periods, so by preventing deep penetration, you may be able to prevent the boy sperm from reaching and fertilizing the egg.

Give it a go. And if you are a man of exceptional length, short stroke the lady.

Another tip, it is also claimed that avoiding orgasm may be the key to conceiving a girl. The female orgasm releases an alkaline secretion which may help boy sperm to survive longer, by creating a less hostile environment. Without these secretions, boy sperm may find it harder to survive, and have less chance of reaching the egg.

I'm sure you already have this one covered though. :)

Here's a good one, rather than restricting your sex life to specific times, when trying for a girl you should aim to have more sex. In the days leading up to your key conception time, you should have as much sex as possible. This will reduce your sperm count, and mean there are less fast-swimming boy sperm available to join the race for fertilization.

['Hamas' Jenkins]

1) Find location of Derby.
2) Find a lab
3) Procure an excess of ethylene and sulfur dicholoride
4) Combine the two underneath a fume hood and immediate seal the container
5) Arrive early to Derby
6) Shatter container on the ground approximately thirty seconds before the race begins
7) ????
8) Profit

[Dunerdr]

:hump:

In all seriousness, to conceive a boy, deep penetration is key, but for a girl, the opposite is true. Having sex in the missionary position is said to increase your chance of conceiving a girl, because it limits the depth of penetration. This in turn, restricts how close to the cervix, the sperm are ejaculated. Boy sperm swim very fast for short periods, so by preventing deep penetration, you may be able to prevent the boy sperm from reaching and fertilizing the egg.

Give it a go. And if you are a man of exceptional length, short stroke the lady.

Another tip, it is also claimed that avoiding orgasm may be the key to conceiving a girl. The female orgasm releases an alkaline secretion which may help boy sperm to survive longer, by creating a less hostile environment. Without these secretions, boy sperm may find it harder to survive, and have less chance of reaching the egg.

I'm sure you already have this one covered though. :)

Here's a good one, rather than restricting your sex life to specific times, when trying for a girl you should aim to have more sex. In the days leading up to your key conception time, you should have as much sex as possible. This will reduce your sperm count, and mean there are less fast-swimming boy sperm available to join the race for fertilization.
:) depth? I'm all tip!

[64 Chief]

My son won 2 derbys with severe wedge shapes and weight as far back as possible. The further back the weight, the greater the gravitational push.