Cub Scouts Pinewood Derby Tech. Specs. Help, Please...

[Mark P.]

Hi,

DS's car now is weighed in at just about 3 ounces. Rules say it can weigh up to 5 ounces.
The design he wanted was more of a sleak kind, which cost him valuable wood/weight. Even though it's not yet painted, it sure does look cool!

Now for the technical specs. question,lol:
Does anyone know if it's permissable to weigh down the car? The somewhat lame instructions that came with the hunk of pine says that accessories such as fenders and spoilers can be added for weight. Where to get these around my area is a mystery.

Can the car be weighted down by other means, such as drilling out a hole and placing a sinker inside, then filling it in and sanding it over?

We've asked the den leaders, and they don't seem to have an solid answer, and unless we hear a definite answer, we're leaning towards leaving the car as is at 3 ounces, and not weighing down to be 'legal'.

Thanks for any help,
-Mark

 

[supergoof]

Try this site....http://members.aol.com/randywoo/pine/

 

[pjlla]

We were told at my son's last scout meeting that, yes, it is perfectly legal to add weight any way possible... as long as it does not weigh more than 5 oz exactly. The wheelbase must stay "regulation" and all four wheels must touch the ground.... other than that it is pretty much anything goes! But double check with your area Den Master..... he/she should have a definitive answer for you!...............P

 

[Pam]

Yes, it is perfectly legal to add weights to your Pinewood Derby car!

Just keep weighing it to make sure it's within the parameters.

A great website for Cub and Boy Scouts is www.macscouter.com

Your local Scout Service Center should have car accessories. You can also order tons of accessories at the official Boy Scout Supply Center - www.scoutscout.org

Good luck - it sounds as though your son's car will be definitely stylin'! Most packs also award trophies for "Classy Chassis", "Most Original Design", "Most Sporting", etc.

 

[Mark P.]

You guys are great! Thanks

 

[JimB.]

Be sure that anything you put on the care is "Pinewood Legal". There is a lot of stuff that you can buy for Pinewood cars that is not allowed on cars that race. For example, you must use the stock wheels that come with the car & cannot have one piece axles.

There are also "Pre-cut" & shaped pinewood bodies that you can buy that are not legal to race. I've always wondered why non-race legal things are advertised for sale in Boy's Life.

Capatilism at work I guess.................

 

[padams]

Our troop is pretty laid back and not so picky so the pre-cut cars are allowed.

Look at hobby shops for weights, decals, etc.

 

[tar heel]

Definitely add weights and get it as close to 5 oz. as possible b/c it will run better if it's heavy.

I've seen cars with pennies taped to the top on race day to get them up to the limit.

Good luck on that car. This is our last year of Cub Scouts (three boys), so my dh has overseen a lot of Pinewood Derby cars and is getting ready to do his last.

 

[tkd lisa]

The reason the "non-legal" stuff is offered is primarily for the parents and siblings who want to make cars too, but they don't have to race them in the official race.

And yes, the answers here are correct that you can add weight. The local post office is a good place to get an official weight, but realize that whatever scale your pack uses will be the official one, even if it's not right. So it's a good idea to have a drill available to remove some weight in case the official scale weighs in a little heavy.

Happy Racing!

 

[jgmklmhem]

Back when I did Pinewood Derby you were allowed to weigh the car down as long as it was under the weight limit. My father and I took the lead shot out of a shotgun shell and drilled small holes in the bottom of the car and added the shot to add weight and then filled the holes with wood glue. Another thing that helps get speed is to polish the axel nails with some sort of polishing solution. My dad was an engineer so he loved this sort of thing and since I liked winning I did all the stuff he suggested and we normally won. I will say though he had the ideas, but made me do the work and let me design the body shape paint scheme etc.

 

[brerrabbit]

When my now 19 year old college Sophmore was in Y Indian Guides they had an annual Pine Box Derby. We lived in the Clear Lake area of Houston with a bunch of Nasa Engineers. You should have seen the cars they had. WOW! Slick, polished, with seven layers of paint and graphite on the axels. My sons car was a standard kit which was a block of wood with two wooden dowls for axles and screws to mount the wheels. I shaved a little wood off one end to give it a front, and drilled a hole large enough to hold some penny's not knowing how much it weighed. He painted it as only a child in Kindergarten could and off we went. On race day at weigh in we were way under weight. I put pennys in the hole to the top and still we were under weight. so I added more and tapped them down with Scotch tape. At race time it was still under weight. Out of over 200 cars, his little homemade, self painted car won. I had Nasa engineers crawling all over me wanting to know the secret. My standard answer was "I don't know, I let him build it."
The truth I never told them was I did three things a friend in Dallas told me made all the difference. 1. I took the screws that held on the wheels and before we put the wheels on I polished the section of the screw where the wheel hit, by putting the screw in my drill and using steel wool to smooth the surface. 2. I deburred the wheels. I made sure the wheels were smooth by taking a knife and removing the little places where the molds were injected with plastic. 3. I used plain old three in one oil on the axels. He won every race by a minimum of three car lengths. Looks are not everything. Speed is.

 

[mom2boys]

My guys will receive their pinewood derby cars next week. They usually spend Christmas break building the cars. This is my oldest's last year as a cub scout. My guys always try to make the cars weigh as much as possible within the rules - makes the car go faster.

 

[Figment22]

Try to get the weight up as close to the maximum as you can. The heaviest cars have the best shot at winning the race, but aerodynamics and weight placement matter also.

There are official Pinewood Derby weights and all other types of official accessories sold directly at the local Boy Scout council and often at the sporting goods stores where you buy scout uniforms. They also sell a type of graphite to make the wheels spin freely. My husband and sons always polished the "axles" (nails) to allow the wheels to spin more quickly.

As an earlier poster mentioned, when you see your official weight at the weigh in, have preparations for either removing or adding some weight at the last minute. Also keep in mind that you really can't add any weights under the car because it has to be able to fit over the track.

Have fun--Pinewood Derby is great!

 

[Mark P.]

Thanks again folks for the advice

Last night, DS and I drilled some holes in the rear of the 'car', and placed steel shot from a shotgun shell and filled and sanded the holes. With the wheels on, we're at just under 4.5oz., according to our scale.
That should leave enough leeway for paint, decals, and possible difference of the scale they'll use.
We're done with it for the time being (leaving today for Disney!)

Technical stuff for a wood car, but it's our first time, and we'd like to give it our best, within proper guidelines

Again, thanks!
-Mark

 

[Amy]

Oh, how I miss the Pinewood Derby! Both of my DS's are in boy scouts now, and the Pinewood Derby was always my favorite.

A couple of tips DH always used when helping the boys with their cars: the car kit usually comes with the axle holes pre-drilled. DH would ALWAYS re-drill the holes because they're not straight, and a crooked car is a slow car.

Also, lubricate the wheels. I'm not sure if it's the official rules or just the rules our pack had, but DH always used some kind of powdered graphite as lubrication - no liquid stuff or oil was allowed.

On race day, be sure to take a glue gun with you (to add weight) and a drill or something in case you're a little heavy. Usually the closer you are to 5 oz. the better.

Good luck!

 

[Geoff_M]

The heaviest cars have the best shot at winning the race, but aerodynamics and weight placement matter also.

Actually, the research I've read says that with the short distances traveled and slow speeds PWD cars move that aerodynamics are almost meaningless. The other two factors you cite are the most critical. The more weight the more speed at the end of the incline. The key is keeping the speed on the flat part of the track. The number one speed killer is side-to-side "buffeting" when the car swerves back and forth on the track and strikes the center divider. By placing the weights at both ends of the car, the less buffeting you'll have.

Polishing the axles (removing any metal "burrs"), and non-liquid lubricants (like powered graphite) are perfectly legal. As for weights, you can use washers, fishing sinkers, etc. Hollow out a cavity in the bottom, put in the weights, use a glue gun to fix them in place.

One important thing to remember is that this shouldn't be a "dad" project. Let your scout do as much as possible. I let my son design the shape and make a tracing of the outline. I'd then do most of the cutting, and he got to do all the painting and decorating. I'd add the weights and he'd polish the axles with a Dermel tool.

 

[Geoff_M]

As a follow-up, here's the research I referenced. If you listen to "Car Talk" on NPR, it's from their web site. It was sent to them after a mom called their show asking for help with her son's car:

Attached is the right information and analysis on Pinewood Derby cars. You may post it with attribution.

The Physics of Pinewood Derby Cars
by
Clifford W. Lazar

My first car design came in second. Then I learned the shape of the race track. My second car design finished first. The competing fathers were aerospace engineers and mathematicians. My opponents' cars were tested in TRW's wind tunnels.

Operating Environment
Pinewood Derby cars travel downhill, initially at about a 45-degree angle, through ambient air, not in a vacuum. The track is composed of two parallel runways, each with a raised center median. The wheels of each car are placed straddling the median of their runway.

The cars are held in place, before the start, by a two-tanged vertical fork that is pivoted forward and away from the front of the cars, until the fork tangs are below the respective medians. The tangs move through two slots in the respective medians.

Air Drag Is a Minor Factor
There is a small air resistance that means a 5.0-oz. car will travel faster than a 4.5-oz. car. At the same time, since the cars don't exceed 15 mph to 20 mph, the relative air-drag resistance between two cars is a minor factor, contributing little to speed. Wind-tunnel testing at hundreds of miles per hour is meaningless.

Major Factors: Rolling Resistance and Angular Momentum
I have tested motor oil, graphite, and 3-in-1 oil. Motor oil is too viscous; graphite is the second most viscous. 3-in-1 has the least viscosity. It also won't last from one heat to another. The Pinewood Derby car manufacturer recommends against using 3-in-1 because it allegedly deteriorates the plastic in the wheels. We don't care if the wheels only last 12 hours. Actually, they last for years. If you don't oil the wheels before each race, they will slow down.

Axles
You want to have the wheels as close to the body as possible to avoid wobble. If the wheel hub rubs against the car body, it will lose energy to friction. This can be minimized by polishing the body as smooth as glass and lubricating the body with 3-in-1 oil.

Angular Momentum
A major factor for the travel time of the car is the angular momentum. If the car doesn't go straight, the wheels will ride up on the median strip, converting forward speed to chattering increased height. You can hear the losing cars chattering their way down the track. The car manufacturer incorrectly recommends that the extra weight be placed in the center of the car. This is like putting a mid-engine roadster in a drag race. Drag racers are long. They try to maximize their angular momentum. Mid-engine sports cars try to minimize the effort required to turn.

I placed the fish weights evenly in two pairs of holes drilled in the front and back of the car. This created a barbell effect, maximizing the angular momentum. My car wanted to go straight.

Winning the Race Before It Started
Most of the hotshot fathers shaped their cars to look like Formula One racers, low slung and aerodynamic. When the fork tangs were lowered by the starter, the low-slung cars stood still until the tangs were nearly rotated 90 degrees.

My car was shaped like a landing barge--a funny sight to see a landing barge beating the Formula One racers.

The landing barge shape meant that when the tang of the starting fork had moved 10 degrees my car was already moving and ahead of the low-slung car, next to it. At 45 degrees my car was already three-quarters of an inch ahead of the opponent. Some of the heats were only won by three-quarters of an inch. The other guy must have done a good job with his wheels and angular momentum. Still, he lost because the beast will beat the beauty...if the physics is right.

Copyright © 1997, by Clifford W.Lazar

http://www.cartalk.com/content/features/Derby/followup1.html

Note: I will add that the use of liquid lubricants like 3-in-1 oil is against the rules! But the rest of his advise is OK.