powdered graphite on the wheels, make the car in whatever shape you want. When you are done add weight over the front axel up to the maximum allowable by the rules. We used to hollow out the bottom of the car and drip molten lead into the space and seal it with wax and paint over it so the car looked sleek. I won a lot of design awrds and a few races in my cub scout days.

Dave

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Dave Stark
dreamcatcher@astound.net
USAC & USAT level 2 certified coach

If you post on the main forum, maybe somebody can point you toward the nearest wind tunnel.

Sounds like fun times ahead. Pinewood derby was hands down my favorite part of cub scouts when I was a kid. I think designing a car should be a fun challenge. Seems like the things to do would be 1) make sure you know the full design rules really well, 2) get the car as close as possible to maximum weight, and 3) get the wheels as well-aligned and free-rolling as possible.

As for graphics, I'll bet you could do some cool stuff with decals printed on a home computer, then clearcoated. Model railroad or model airpane websites might have some ideas.

Maybe post some pics as you get going with this project.

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Over 4.5 years bike crash free.

Sand the nails (axles) with fine sand paper to smooth burrs then graphite powder. I was told also to have one front wheel slightly off ground to lessen resistance. Less resistance equals speed. I think the best place to add weight is around middle of car. I hollowed out a spot mid bottem and filled over with wood filler Uh um I mean my kid did. I shaped mine I mean my kid shaped his like a 5 series BMW with a wood chisel has a cool little spoiler tail in the rear. Almost needed stitches after one mishap. Also if you go to a hobby shop they have all kind of acceseries for the car to make faster. We bought a lead skeleton man driver with a steering wheel and some cool flaming skull transparent stickers. Painted a nice glossy black with the flames looks pretty cool. I was thinking of doing another like the Animal house "eatme " cake then have the death mobile come out half way down shoot. Fathers in my town our a little to uptight for that though.

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For weights, we bored out holes in the bottoms of our cars and filled them with pennies, then plugged them with dowels. Brought supplies necessary to pop it open, remove a few pennies and reseal it in case the scale at the weigh-in was reading a little heavier than our scale.

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Over 4.5 years bike crash free.

I melted lead sinkers.

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Karma has some good thoughts. I'll add a couple. Paint job matters. A lot. The kids compare the look more than the performance to a point. Clear coats and hand rubbing with car wax if you are not too pressed for time are the difference between a good car and a great car. Also remember that there are a number of "events" at a derby. In addition to the straight downhill race, there is also a jumping event. Make sure your car will handle some banging around. To that end, you want to make sure your weights are secure. Use a postal scale to get right on the max weight. Since there may be a variance in your scale and the official scale, design in the ability to add and subtract a bit of weight. Your goal is the max allowable. You will get looked at crosseyed if you are under weight. You can be everyone's hero if you bring along a hot glue gun and extra graphite.

Remember to let junior get in the game! He can polish the wax ;-)

Good luck.

Thanks everyone. I'll post some pics when finished. We just cut the car out today and he did some sanding (I'll finish it when he goes to bed). I'm hoping to prime it tomorrow night and then paint on Fri. The race is next week, so I do not have a lot of time. I wanted to kind of do it at the last minute so he did not wreck it until after the race. I like the penny idea. I have some sinkers I was going to melt and then when I got close I would put some of those little sinkers in that I could add/remove as needed.

I'll look into the making sure one wheel is off the ground.

Per official rules the profile of the wheels can't be changed (i.e. ground narrower to a point) but what I did was to take the dremel shaft that holds a cut off wheel and mount the car wheels to it. Then put it in a drill and spin the wheel against some emory cloth. This gets rid of any irregularities in the surface of the plastic without changing it's shape. Get the weight as close as possible and the straighter it rolls the better. Use graphite. Aero design doesn't mean much, I've seen cars shaped like a block do well. Both my sons were in cub and boy scouts and their cars always finished in the top 10 with a couple of top 3 finishes. Let your scout do as much of the work as they can safely do, it's usually pretty easy to spot the cars where the parent did all of the work.

i seem to remember the back of my car hitting the track on the bottom of the hill. i think i had flipped the car around to make it look "cool." not such a good idea. also, if cosmetics is important, don't make the car's leading edge too thin. i ended up having mine cracked off after hitting the timer gate at the end of the race. didn't seem to affect the performance, just looked ugly.

level of importance:
1. proper weight (most serious competitors will have this down)
2. wheels (this is where the race is won)
3. aero (a distant 3rd)

THE most important tip:

- Get the car at maximum weight with the weight as far back on the car as possible. The "balance" point of the car should be ~1" to 1.5" in front of the rear axle. This maximizes the potential energy of the car as it sits at the start gate...any further back with the weight and the car will want to "pop wheelies". With the weight back like this, once the car hits the flat portion of the track, it'll pull away from a car that has the weight further forward.

Second most important tip:

- Reduce friction in the wheels/axles wherever possible. This means polishing the axles and the wheel bores, along with applying graphite and "running in" the wheels by spinning them. Also make sure that the car runs true and the wheels aren't "fighting" each other to make the car go straight. Spend a little time getting the all the axles "aligned" to the body and each other...

My boy has his last Pack pinewood derby on Saturday. We where working on the wheels tonight :-)

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I thought aero trumped weight? ;-)

Weight and graphite are what did it for me as a kid. My dad did the whole thing; the car took 1st for looks and on the track!

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Tom's got it right. Lowest possible friction for the drive gear and as much weight as you're allowed to maintain speed at the end. The race is won or lost on the flats. Pinewood derby is a ball!

In the "time flies" category, I remember my Godson's Tiger Cub days like they were yesterday and today he's a freshman in college and an Eagle Scout.

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"Far better it is to dare mighty things, to win glorious triumphs, even though checkered by failure than to rank with those poor spirits who neither enjoy much nor suffer much, because they live in a grey twilight that knows not victory nor defeat."

Theodore Roosevelt

Also if you hve a treadmill set it up on the tread mill and run it for 10-15 minutes to break in .

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Wow. Great idea!

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"Far better it is to dare mighty things, to win glorious triumphs, even though checkered by failure than to rank with those poor spirits who neither enjoy much nor suffer much, because they live in a grey twilight that knows not victory nor defeat."

Theodore Roosevelt

I love your post. I was going to comment, but I think displayed that the whole competetition aspect of the pinewood derby is between whose *father* can build the best car.

Despite me being a mechanical engineer, my father was not very handy. He grew up very poor with a father who was pretty much non-existent, so never got to play with power tools, etc. We built a pinewood derby car. It was pretty basic and finished dead last....not even close to second to last. DFL! I was crushed. Needless to say, I didn't think much of cub scouts. Kind of reminds me of little league baseball.....

Anyway, to the OP, best of luck. With the advice on here, sounds like your kid is going to design a very nice car. ; ^ )

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-----------------------------Baron Von Speedypants
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I remember going to my first derby and you can tell every kids father did their cars. I did let my kid decide on shape of car he wanted and the color. I did let him sand the car a little and paint although I held his hand and guided him on touch and going back and forth. He even put wheels on. We tried taping and painting flames on car. The paint just bled through so we resanded and painted again. he did have a hand in building car. What helps a kid more crushing his confidance by having a ugly slow car or giving him confidance by having him help a little and having a good looking halfway fast car? I will opt for later with my child till he gets a little older. Its to much to expect a 5 year old to shape a car by himself.

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Thanks for the posts everyone. He helped me trace the outline of the car and has done most of the sanding. My neighbor has a wood shop so he did the actual cutting of the car. I have a coping saw that I could have done it with, but it was easier this way.

We are going to prime tonight and paint on Fri. He will do all of the priming/painting.

IIRC from when I was a kid, I did more and more work on the car as I got older. I'll post pics when we are done.

Thanks for the tips on where to put the weight.

These replies are exactly what is wrong with this sort of father/son activity. You get a bunch of douchebag fathers trying to engineer a freaking missile car. The exercise is about letting 7 year olds have fun and trying to be creative. 7 year olds dont have a clue about powdered graphite, melted lead, titanium running boards, etc, etc,. Years ago my sons car was by far the ugliest (he did all the painting), slowest, piece of wood in the competition. Was next to last in every heat he ran it in. But he did all the work on it and designed it. 15 years later he graduated from MIT and he still looks back at the project as HIS first true science project.

Ever see the sitcom where they all had to build robots for science fair. The dad eventually gets really into it, but at the fair breaks down and gives a speech to the entire room about how rediculous these things are since the fathers do all the work. He admitted to building his kid's robot and urged the others to do the same.

In the end, his kid got an F for cheating and everyone else got an A.

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-----------------------------Baron Von Speedypants
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Yep, it's one thing for the dad to offer advise on how to build a faster car, it's another for him to take over and do all the work. I had one of those dads that didn't know which end of the hammer to use, but I was rather mechanically minded so I did it all myself. On my own I made sure the axles where straight and aligned to each other. I lightly sanded the wheels to get the burs off the riding surface and used graphite on the axles. For getting the car up to weight I used a spade bit to drill a hole in the middle underside of the car and filled with lead split shot sinkers held in with glue. For painting I got the best results with sanding sealer first and then paint.

He is pretty young (actually turns 7 next week). I do not think it's a good idea for him to use any sort of sharp tools so no chance of him doing any cutting. Sanding and painting, fine. He called the neighbor himself to see if he could cut out the car.

I'm not the woodworking type anyway, so there will be no chance of the car being over-engineered.

I look at it as a father/son activity.

Wow, was not sure which post to reply to but figured this was the best one. 7 is young for pinewood derby, my Daughter did her first yes ,HER there girls scout troop does it, in 4th grade 10 yrs old. I made the first prototype, and then she built 3 more until the final one. Here are some pics of her prototypes.





I used this to teach about friction, gravity, normal forces, taught her to polish her axles and wheels, how to place the weight and why. Showed her how to sand and paint.

She did everything on her final car, and it was the best looking one. Unfortunetly Im at work and do not have a pic of final car.

Last year I started working with her sister at age 8. Simpler car but she did it all and knows why she did it.

Don't think the Dad's do all the good looking cars. Some do, some buy them on ebay. Some actually spend 20 to 40 hrs over 4 or 5 weekends working with their kids.

I think this year I will have all three in the shop, 7, 10, and 12. The 7 year olds will be very simple, and probably have her hand cut it if possible, gotta see what she wants for a design.

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Just Triing
Triathlete since 9:56:39 AM EST Aug 20, 2006.
Be kind English is my 2nd language. My primary language is Dave it's a unique evolution of English.

Well looks like im a bit late to help you. There are several forums out there on this, as there are actual leagues that run year round, and other forums just for Boy scouts.

The first thing to find out is what is legal, what do your rules call out. If they allow for a lubricant that is dry on race day, use Krytox or other type of lube that goes on wet but then you remove it all, works better than graphite for under 10 runs. DO NOT Break in this lube. If you can only use dry lube, there are several varieties of lube out there with mixes of graphite and something else that is better than pure graphite (smaller particles).

Center of Gravity 1.2 - 1.5 " in front of rear axle as mentioned has proven good. Get your axles as far back as possible to get the CG as high on the track at the start as possible (maximize potential energy). If you have to use the slots, turn the car around from whats pictured so the front end is longer than the back. If you can make your own slot but maintain distance between axles, move them back so the rear wheel is flush with the back of the car.

Rub graphite into the side of the car where the wheel will touch.

Can you mod the wheels or not? Polish the wheel surface, Remove the mark left by the mold (sand is smooth) o the tread part of the wheel.

have a small amount of weight you can add or subtract (pennies are simple and cheap) at weigh in come in a bit heavy and lighten until 5 oz NO LOWER.

But ultimately the most important part, is WHEEL ALIGNMENT. Test roll the car on the floor with a straight line and see which way it pulls, try to get it to go as straight as possible, (reduces friction losses of hitting the center rail). Go to the forums on how to best align, its an art not a science and takes time and patients.

As I stated above, these are all points my daughter can explain how to do and why you do them. Though the wheel alignment is still one we are not good at cause the cars have been finished to late, and she is done working on them. So not much goes into alignment.

Finish, sand sand sand. Then get some spray paint. Spray paint is easy to do and by far the best finish. There is some automotive spray paint out there that allows metalic looks, multi chromatic ... Kids even a 7 yr old can spray paint and have a finish that will look awesome (assuming they paid the price and sand sand sand). After the car above, my daughter went to a much simplier car the next year that was A LOT easier to sand.

Remember have fun, its not about the race or the car... its about spending time with your kids, teaching them skills and learning togeather.

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Just Triing
Triathlete since 9:56:39 AM EST Aug 20, 2006.
Be kind English is my 2nd language. My primary language is Dave it's a unique evolution of English.

Years ago my sons car was by far the ugliest (he did all the painting), slowest, piece of wood in the competition. Was next to last in every heat he ran it in. But he did all the work on it and designed it.

This sounds like my Pinewood Derby car. My dad was very handy with tools and woodworking, but told me that I had to build my own car so that I could learn about responsibility and taking pride in my own work. Of course, my car looked like a piece of crap next to all the others (since the other dads either helped or built the cars themselves) and even fell off the track on one of its runs. I hated Cub Scouts.

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"You can never win or lose if you don't run the race." - Richard Butler