pinewood derby

Hi,
I'm in a predicament: I helped a friend a few years ago with a small detail on a pinewood derby car he was building with his
daughter, and he won the tournament with it! That was a fluke, but now my kid wants to race, and you can guess what her expectations are...
Any thoughts on how to build a fast car are welcome, but I'm mostly interested in hearing ideas about how to prepare the wheels and axles. The kit we have to use contains 2 steel axles of about 1/8" in diameter and four plastic wheels whose hubs are a loose fit on the axles. Interference with the body of the car prevents the wheel from moving axially toward the car centerline. A plastic snap ring fitting in a groove at the outboard end of the axle prevents the wheel from falling off in the other direction.
Rules are nebulous. I think we're expected to use the wheels and axles from the kit and the car can't weigh more than 8 oz. And that's it. This is a low key event, and I want this to be a father-daughter project, so I don't want to go overboard.
What I have in mind is minimizing friction through judicious alignment and smoothing and lubrication. Any suggestions on how to accomplish this? What sort of lubricant should I use?
Thanks for any and all ideas.
John Blinka
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You, a master builder with a 100% win record, ask US for advise?? <G>
Preferred lubricant seems to be dry PTFE powder. Micropolish the axles. I'd balance the car weight so all wheels carry the same weight. No other suggestions.
John Blinka wrote:

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Profile the wheels so that they are the same shape and that you have a minimum contact patch with the track. (less rolling resistance.) Use the round "dowel" type weights, you can find them at hobby shops that have the Pine wood derby accessories. Drill holes in the car to mount the weights at a 20+ degree angle from horizontal with the weight pointing down toward the front of the car. (weight transfer from the bottom of the hill to the flat part of the track.)
Radius the axles and the wheels where the axles head retrains the wheels to match and have good clearance. Put a ton of PTFE there. That is the big friction point.
Line up the wheels to the car to try and get them as much in the same plane as possible and in a good relationship.
If you really want to be a smart ass get some brass tubes, some steel balls slightly smaller than the tubes. Seal one end of the tube, put in the balls and then fill with oil, seal the other end of the tube. Now you have a movable weight system that won't rattle. Mount that assembly at an angle in the car...low point toward the front. This works great...but is considered a cheat in most scout troops.
Oh..test test test....keep adjusting the car and running it down an test truck and time it. Micro seconds count in pinewood derbies.
Won a 2nd place first time out, 1st place the second year.

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K. A. Cannon wrote:

That idea appeals to my excess of engineering education. I was wondering how to gain a little extra in the distance through which the cg drops. Wouldn't you have to invert the car before setting it on the track so the balls are at the top at the start? And wouldn't you have to size the balls so that they dropped in the tube in the time it takes for the car to run the race?
John
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Rex B wrote:

I'd take a different approach...
Rig only two wheels in contact - opposite front and back.
Less drag is less drag, you know...
Richard
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Rex B wrote:

Looks like MSC sells aerosol cans of this stuff. That's what I'll get.

I've never polished anything. What sort of abrasives are appropriate?

That makes sense, but might be hard in practice. You'd need a pretty flat surface and some way of weighing corners to some small fraction of an ounce. Maybe you could get at the same result indirectly by taking some practice runs, seeing if the car runs straight, and adjusting the "suspension" somehow until it does run straight.
John
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wrote:

Just a heads up. Most of the aerosol PTFE's (at least the ones that I've used) have a solvent to dilute them. This solvent has been known to melt plastic. I've personally seen the results on a wheel and it's not pretty.

Fine emory cloth and finish with crocus cloth (if you can find it).
Wayne Cook Shamrock, TX http://members.dslextreme.com/users/waynecook/index.htm
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wrote:

Here's what I did: On the night of the big race the car still has to be weighted. 1/4" dia lead fishing weight works well. I did not want my son drilling the holes as the drill could pass completely through the car and into his hand. Instead, I drilled the holes and was the one getting the wound cleaned and stitched up. Save your child from this outcome and let your brother drill any holes so you can watch the race with your child. ERS
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Eric R Snow wrote:

Most decent hobby shops have Woodland Scenics Pine Car parts.
They have several different shaped weights with snap off parts to just screw to the bottom of the pine car.
Some places have a 5 Oz weight limit.
Whatever the limit is you want the car just under the limit.
Hugh
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wrote:

Where's the fun in that? My son got to see first hand (so to speak) what some of the inside of my hand looked like. He got to see fat and connective tissue. Now that's instructive! ERS
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Polish axles, and make sure there is no stamnping or press marks evident (like the marks around the head of a nail from forming)...Ensure your wheels are in alignment, as alignment is a big drag and every little bit helps.....Get the weight dead on the max. Even if you have to buy another kit, make sure wheels rotate freely but not wobbly. PTFE is the lube I would go with. True up the wheels cirucmference and eliminate any mold flash etc.round is much more efficient than egg shape when it comes to wheels...You can possibly machine a V shape to the wheels profile so the tread is the point of the V, which will eliminate even more frictional loss.....
Sounds like a lot has changed since I fooled with them..5 oz was max, and they used sheet rock "blue" nails for axles. I have a few kits up in the attic form years gone by, one is circa late 50's early 60's and one is from the 80's and another the early 90's........The later 90's has rounded head pins for axles.....I used to use stainless steel rivets with the wheels bored and trued to fit for my youngins axle. He was doing fine in all the heats, but then kids being what kids are he and a few others had to start pushing them on the concrete floor etc, so much for trued V shaped wheels, but he still did fairly well....
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John Blinka wrote:

I just got finished helping my son do his Boy Scouts pinewood derby car. From helping other dads over the years I can tell you that the previous posts were right on the money. If you can, true the wheels. I pushed the wheel on a .099 gage pin and took very light skim cuts in the Hardinge to true the OD to the center hole. There are ridges on the nails from the cold heading process on both the diameter and most importantly under the head (like a parting line). I skim cut these off with a thin bit in the Hardinge to clean up the ridges and parting line and then polished the OD of the nails where the wheels will contact. I don't use the saw slots for the nails. Instead I predrill .078 diameter holes for the nails in the Bridgeport to insure absolute perfect alignment. Do drill up to high or the car won't clear the 1/4" high track guide. The best lube is spray on Teflon. Do the nails and wheels but tape the ends of the nails so they wont slip out of the car when you drive them in. Lastly, add enough weight (anywhere) so you are right at the limit. For the Boy Scouts thats 5 ounces.
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Narrowing the tire tread to a V has three benefits: 1.) Lowers the moment of inertial of the wheels, so the accelerate faster. 2.) Cuts air resistance of the wheel. 3.) Lowers rolling resistance.
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Leo Lichtman wrote:

Technically, we cannot make this type of modification. A little truing up we can get away with but major changes like this to the wheels are expressly prohibited in the rules included with the kit. Besides: According to the experts air resistance has been discounted as irrelevant at these speeds . I don't buy into the lower rolling resistance theory. The only one I'm buying is the rotational inertia effect but I'm going to double check with the expert (chief engineer).
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Leo Lichtman wrote:

Maybe. A few decimals down...

At these speeds air resistance is a small part of it.

I think this is the one that matters.
However you can get away with it...
Richard
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: :I just got finished helping my son do his Boy Scouts pinewood derby car. : From helping other dads over the years I can tell you that the previous :posts were right on the money. If you can, true the wheels. I pushed the :wheel on a .099 gage pin and took very light skim cuts in the Hardinge :to true the OD to the center hole. There are ridges on the nails from :the cold heading process on both the diameter and most importantly under :the head (like a parting line). I skim cut these off with a thin bit in :the Hardinge to clean up the ridges and parting line and then polished :the OD of the nails where the wheels will contact. I don't use the saw :slots for the nails. Instead I predrill .078 diameter holes for the :nails in the Bridgeport to insure absolute perfect alignment. Do drill :up to high or the car won't clear the 1/4" high track guide. The best :lube is spray on Teflon. Do the nails and wheels but tape the ends of :the nails so they wont slip out of the car when you drive them in. :Lastly, add enough weight (anywhere) so you are right at the limit. For :the Boy Scouts thats 5 ounces.
Add any weight near the back of the car so that the added weight starts off higher on the ramp and gives a longer push. Shape the front of the car so that it contacts the starting barrier as high up as possible (a reverse wedge). The barrier rotates down to release the cars, so the car with the highest contact point gets released first.
Furniture wax (Pledge(R), or similar) makes an excellent lubricant for the wheels -- much better than Teflon(R). The Teflon would hold up longer, but how many miles do you expect this thing to go?
--
Bob Nichols AT comcast.net I am "RNichols42"

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Is this a sanctioned event? Pinewood derby (Cub Scouts) use 5 oz weight. Need max weight by adding lead. Verify on Postal scales. Suggest Max weight and take a little cordless drill to take weight off if necessary (will help others do the same) Car should be slightly rear bias on weight. Axles on pine derby cars have two rough edges that need careful deburring and polishing. Wheels need as much space apart as possible to prevent scrubbing the guide rail. True wheels seem to work as good as regular wheels as they wobble so bad. Rules won't allow wheel bushings or oversize pins.
Rules require dry lubricant. Most use dry graphite to lube the axle. Take extra. The little ones will try to run the wheels off of it, this will screw up the alignment. Need to roll straight.
Most have adult and Jr. division as well as outlaw (no rules). Some are judge in different categories. Best of show, most original, fastest, prettiest, whatever. When we did it we made sure everyone won a certificate identifying their car as special in some category.
Hard to have fun when your trying too hard. Keep in mind wins are usually in just inches but having fun is priceless.
Easiest car to fab and polish would look like half a football. Kinda like the cars they used on the salt flats made out of a aircraft fuel tank except cut in half.
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John Blinka wrote:

<snip>
Sorry, I can't help you with your predicament, but you might like this story:
http://www.geocities.com/~pack215/thesmellofvictory.html
Not that I think you're like the father in that article, just that I enjoyed reading it and it's related to the topic.
Good luck!
R, Tom Q.
--
Remove bogusinfo to reply.

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Thank you for the great story. I can relate, having been raised by a working mom.
James
On Wed, 25 Jan 2006 20:00:41 -0500, Tom Quackenbush

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Tom Quackenbush wrote:

Thanks, that was a good read. In my cub scout days we raced balsa wood rockets that were suspended from a long horizontal wire and were powered by rubber band driven propellers. The rules stipulated one rubber band, and the racer had to build the thing himself. A lot of perfectly built rockets with a lot more rubber bands showed up and I finished dead last. It's fun to think about all the things one could do to make a pinewood derby car go fast, but my daughter and I are racing against my friends and their daughters. I don't want to be "one of those dads" to them.
John
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