Building a Pinewood Derby (Race Results)

[Jeremy airjer W]

My boys and I had a lot of fun building our first cars last year. We did pretty well at the race with one of the boys finishing 14th at regionals.

This year I thought I would share the building process.

We started by deciding on a shape and paint scheme. Ethan and I decided on wedges this year and Carter decided on a funny car looking shape. I'm hoping I can pull off this paint job!

The car is a pine block with two slots for the axles. For the most part these slots are square with the axles and for the boys cars they are fine. I like to drill my holes with the left front off set so that it will not make contact with the track. One less wheel = less resistance. The jig makes quick work of this.

This is the block with the all the holes drilled. Notice the left hole is higher than the right hole.

Next I ran the back of the car through the router table to get the rounded back end.

I know I am going to have to add a lot of weight. Most of it will be in the back. I am expecting around 2.5 ounces so I'm drilling the holes for the weights now.

The layout is to scale and I printed them out and used the sides as templates to cut out the bodies shape.

Now the sanding begins. The boys love to sand and did a pretty good job on there cars with only a little fine tuning needed.

The cars are finally primed. I had issues with the paint lifting last year and I have a feeling spray on primer was soaking in to much and not sealing the wood. This year we are brushing on the primer in the hopes of getting better end results.

The next step will be paint as well as polishing axles and getting wheels ready. I'll add the posts as we get them done.

[MJ1657]

I still have one or two of my pine wood derby cars stuck in a box somewhere. They were alot of fun.

Who is having more fun Airjer. You or your boys????

Good luck!

[Jack Peterson]

those look identical to my old pinewood derby cars. the weight in the back always is the winner. i think we used bolts? i can't remember. all i know is that I was a top contender every year that I had the weights in the rear of the car!

Nice work.

[LMITOUT]

Great thread. What are the rules for the car? Weight, length, height, etc?

Looking forward to the rest of the story.

[Jeremy airjer W]

We all have a lot of fun building these.

Car Specs:

A. Width - Not to exceed 2 3/4 inches

B. Length - Not to exceed 7 inches

C. Weight - Not to exceed 5.0 ounces on scale accurate to 1/10 ounce.

D. Height - Not to exceed 3 inches

E. Center Rail Width Clearance – Must clear center guide rails, typically no less than 1-3/4 inches minimum.

F. Bottom Clearance - No less than 3/8 inches from track surface. Fender flairs with less clearance are acceptable as long as the center rail width clearance is the same in rule E. Weights are preferred to be inset in the body or on top of the car to aid in a safe stop at the end of the track.

G. Wheelbase –All cars must have a wheel base no less than 4", with the two rear wheels being positioned directly across the body from one another and the two front wheels being positioned directly across the body from one another.

H. Front End – Depending upon the track, the front of the car may rest against a short starting pin. We therefore require that the front bottom of the car which rests on the pin is no higher than 1" above the track. The front end must be at least ½ inches wide in the middle. No part of the car can extend beyond the starting pin.

The full rules can be found here

http://www.northernstarbsa.org/Forms/Activities/PinewoodDerbyRules.pdf

It's kind of fun searching for grey areas!

The biggest change this year is no lead weight. The round tungsten weights worked well for us last year so we are using them again.

[Surface Tension]

Jer, nice thread and I can't wait to see what the progress.

Oh I miss the excitement of building cars with Jr.

We had a class for parents as well. Fun and competitive for sure.

I see your using some of those secrets to make the car faster.

I went with the weight low and in front of the rear wheels.

Your weight high and rear might give you a better slingshot effect or it might pop a wheel in the transition.and fly off the track.

Here is our last car "CHEEZ-IT"

[harvey lee]

I remember those days building a car with my father. Fun times.

Good luck to you Jer with the boys.

[Jeremy airjer W]

I like that body shape Frank. I might have to use that one of these years. Of course I will need to consult with a buddy who happens to be an aero space engineer to see how good it would be going through the air.

[muddpuppy]

"We started by deciding on a shape and paint scheme. Ethan and I decided on wedges this year and Carter decided on a funny car looking shape. I'm hoping I can pull off this paint job!

"

Could try and use the POPCORN bag as a body wrap. My son went with a stars and stips body wrap on one of his cars and it won the best looking. He didn't get into all the speed tactics though.

[pureinsanity]

Could one make a rear wing on the car for more down force?

[Jeremy airjer W]

You can but down force isn't an issue in a straight line. It would also disturb the air flow off the back of the car and slow it down.

I wouldn't think aero was a big deal but I had three cars last year, one of them was shaped like a bus and the other two where stream lined. Everything else was identical as far as weight, wheels, axles etc. The bus shape was considerably slower. Ethans car was almost identical to mine but it had a rear spoiler shaped into it. It was a couple of thousandths slower than mine without the spoiler.

[Jeremy airjer W]

It's time for the axles and you may be thinking what are you doing to the axles? I'm reducing friction by removing burs and polishing. Overkill, maybe but I think setting the track record at 2.432 seconds for last years competition has to say something.

These are the axles in there stock form. If you look closely you will see the burs left by the manufacturing process. These are the enemy and exist not only on the shank but on the head.

Since I will be cambering the axles the first step is to mark them so that they can be tuned and aligned in the future. I ground a small slot in the head with a dremel cut off wheel and then used a blue sharpie to make the mark more visible.

The next step is to file down the burs.

Next the polishing begins. From left to right are 500, 1000, and 3000 grit sandpaper and 8000 grit diamond polish. This is the first time I tried the diamond polish and not really sure if it makes that much of a difference after the 3000 grit polish.

The axles after polish. In the bottom photo the axle head on the left is the polished axle. I like to do the heads just to give them a little bling! You can see a pretty big difference in the before and after.

The last step is to camber the axles. Why camber them? The rules state you can't change the shape of the wheel so the tread must remain parallel with the hole for the axle. The rules don't say you cant change the angle of the axle so if I camber the axles it will make the inside edge of the wheel the only part of the wheel to make contact with the track instead of the entire surface area of the wheel which = less resistance.

It also help with the tracking of the car. I want the car to track to the left or right all the time so that one of the front wheels always stays in contact with the rail of the track. A car that constantly turns left and right while going down the track has to go further and every time it bumps the rail it will slow down.

There are two options either 2.5 degrees or 1.5 degrees. 2.5 degrees is recommended on the rear axles but since I have not tried this before I'm going to run with the 1.5 degrees on all four.

It took about an hour to finish all four and believe it or not I left a few details out. I have to keep some things a secret!

[TooTallTom]

airjer, it's fun to see your project in progress. I bet it's even more fun to be working on it with your boys.

I look forward to more updates...

[Jeremy airjer W]

I'll admit I cheated a little this year. I found blank decal sheets that you can use in your inkjet printer. I printed off all of the graphics, topped them with a clear coat, and then applied. I still hand pin stripped the yellow and blue lines. I think it turned out pretty well.

[pureinsanity]

Nice job on the decal, even though you say you "cheated" decals are not easy to install. I think you did a great job. I wont ask to see the bottom of the car though

Nice work, I am enjoying this thread!

[Surface Tension]

Looks very nice Jer.

I think Trails End should give you a free case of Popcorn as a sponsor.

[Jeremy airjer W]

So lets talk about the wheels. There is a grey area in the rules that says you can lightly scrape, sand, polish the wheels to remove imperfections. There are a few stipulation that limit the amount you can remove. The new wheels are pretty smooth and pretty true compared to the old wheels. In the photo below you can see all three. The one on the left is a wheel that I did, the middle is an old wheel, and the one on the right is a new wheel. (I should add that the boys cars are using the stock unaltered wheels)

The first step is to make the tires perfectly round and flat.

Next I make sure the inside edge is perfectly flat.

After the truing process I mount the wheel in the drill press and start a polishing procedure simular to the axle polishing process.

The last step is to insert the axles and add a dry lubricant.

If you think I am crazy the results speak for themselves. If you put a stock wheel on a stock axle and spin it you will get 10 to 12 seconds of spin time. After all the modifications I average around 20 seconds of spin time with the best wheel at 26 seconds. The slowest wheel will be the one I put in the offset hole so it will never make contact with the track. The two fastest wheels will go on the back.

The last step will be to insert the wheels and axles into the car and align it so that it tracks slightly to the left. I will also be offsetting the wheels so that the only wheel that makes contact with the guide rail will be the right front (the wheel that is offset).

[Surface Tension]

No your not crazy.

Very nice guide Jer and I like following the process.

Your not done though, you need to video the race and show us.

[Dozer]

Arnt the kids supose to build these cars?

[Jeremy airjer W]

My boys built both of there's. The only think they didn't do was cut out the bodies with the band saw. Otherwise they designed there own cars, painted them, did all the drilling, polished there own axles, and assembled there own cars.

[TooTallTom]

Arnt the kids supose to build these cars?

I think the kids ARE building the cars. All three of them.

For the record, I think there's nothing wrong with being willing to be a kid sometimes as an adult. I think it's good for you.

[Jeremy airjer W]

That and they are pretty fun to build.

I like competition and I like the technical side of it. Most people would look at it as a block of wood with wheels but there is so much more to it. You can have just as much fun building a basic car and have it be just competitive as the ones that have all the little tricks and mods done to them. They may not get a trophy but you expect a few of them to make it to regionals.

The best part is you never know how it will go until race day!

BTW, I am starting final assembly as soon as I hit the submit button. I'll have the info up either today or tomorrow. Our Derby is on Saturday. I'll let you how it goes sometime this weekend.

[TooTallTom]

I'm looking forward to the report.

[MLee]

What length track are you running?

My boy had the fastest time in his pack of 2.88 on a 42' track

[Jeremy airjer W]

I don't know the length but I know we are pack 246. If anyone happens to know what length

there track is.