Pinewood derby question?

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I have heard and it makes sense to raise one wheel up a little bit to reduce friction, but which wheel one of the rear wheels where the weight is or one of the front wheel and hope it goes straight with one front wheel? Joe
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It will steer towards the side rail with an unbalanced situation like you describe. If any thing you will be increasing friction. The only real friction is between the axel and the wheel. If you eliminate 1 wheel the other 3 wheels will have more friction. Use tons of graphite on the wheels and axel.
A trick I used was to put the nail/axel in my drill with the wheel mounted and added lots of graphite. With the axel spinning quickly in the drill and holding the wheel all surfaces became polished/burnished and loaded with graphite. My son won 2 trophies that year with that car.
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He must have been proud of all the hard work you did!
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LOL.. He did the rest. I was not crazy about my 7 year old with an electric drill with a nail chucked up in it spinning between his fingers.
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Leon wrote:

Fair enough, just giving you a hard time ;-)
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Leon wrote...

Joe, you can't raise a rear wheel, or the car will sit cocked.
You can raise a front wheel and adjust the steering by tweaking the other front wheel so that the car runs true.

It doesn't increase or decrease friction (all else being equal) to ride on only three wheels. The total drag from friction is the same in both cases. However, potential energy can be saved if the car runs true down the track, because the lifted wheel will not be rotating full speed when the car crosses the finish line. The lower momentum of that wheel must be conserved, and the only place for it to go is into the forward momentum of the car. So, there is some potential benefit from raising a wheel.
I don't mean to downplay the importance of lubricant and polished bearing surfaces. That's paramount.
Jim
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On Thu, 5 Jan 2006 20:33:30 -0700, Jim Wilson

We will not be raising no wheels, mon.
We playto the straight and natural blue.
Tom Watson - WoodDorker
tjwatson1ATcomcastDOTnet (real email)
http://home.comcast.net/~tjwatson1 /
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and any force you would save by not generating it would be a drop compared to the rest of the forces.
I have heard that raising a wheel reduces friction, but the odds of having it track as well as 4 wheels is not good.
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Toller wrote...

Not kidding. It can produce a measurable result. That's not to say it's particularly important in the grand scheme of things, and I did try to make that clear.

Well, it doesn't reduce friction, and it is true that it's harder to get the car to track as well with only three wheels. But not impossible.
Since I haven't seen it mentioned here, I should point out a very important performance factor that is usually neglected, and that is the track itself. A car which could perform extremely well on a top- quality track often fares poorly on a bad track. For example, on a bumpy track, you can't push the weight back as far as you'd like (and could get away with on a smooth track).
Jim
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The increased friction would be where the wheel and the axel come in contact with each other. The carried weight would be 1/3 greater for each wheel and axel if 1 wheel were eliminated.
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Except for paying for the weddings, I am now more glad than ever that all I had was daughters.
--
www.e-woodshop.net
Last update: 12/13/05
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Leon wrote...

True. The axle load on a car with four wheels would be 1/4 the car's total weight. It would be 1/3 on a car with a lifted wheel. But the axle- wheel friction is directly proportional to the axle load. That is, for any given wheel:
f = c * (1/4)m = cm/4
where f is the friction, c is a constant, and m is the car's weight.
So t_4 = 4f = 4cm/4 = cm
where t_4 is the total friction from wheel drag in the 4-wheel case.
Similarly, with three wheels, as you noted, we have, f = cm/3, but now there are only three wheels, so the total friction is
t_3 = 3f = 3cm/3 = cm
Since c is the same in both scenarios, t_4 = t_3. That is, the total friction is the same in both cases.
Jim
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Yeap, the graphite is key, as well as, making sure the wheels are aligned straight. Make sure to roll along a flat surface and it maintains a true straight line. Trophies two of three years. The one year an axle came lose. Ha!
Thunder
On Thu, 05 Jan 2006 20:24:19 GMT, "Leon"

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" making sure the wheels are aligned straight."
When our sons did this, I sawed two kerfs in a 2x4 block and set the wheels in them for alignment. They did well, years later I did the same for a grandson, his didn't do worth a darn.
Walt Conner
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Sounds like a good reason to buy that new tablesaw you've been wanting.
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As a grandfather I have made many Pinewood Derby cars for scouts in our family. The kids designed them, I did the body work, they painted and finished wheels and hop-up. We had many winners. My daughter was Den Mother for her son's Cub pack and helped run the derby. In her final year she entered the race against the dads, and she smoked them! The track always had a 3/8" center strip to keep cars on track so our main concern was clearance underneath the body. Glenn
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If you search the Internet, you should find a site with all kinds of tips for faster cars, our son did but I don't know where.
"He must have been proud of all the hard work you did!
This is supposed to be a father/son project, unfortunately some sons don't get to touch them.
Scoutmaster
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wrote:

I think that this depends on the judgment of the parent and the age of the child.
Last year, the first year that my boy was in a PineyWood Darby, he was seven, and I let him draw the car and then I roughed out the blank on the bandsaw, according to his drawings.
He then used the rasp and various grades of abrasives to bring the car to its final shape.
He did the finishing.
I knew, nothing about the preparation of the wheels and axles.
He came in Third in his pack and was well satisfied.
This year he will be Eight. I will explain the physics of weight placement, friction, etc.
He will true the wheels and polish them.
He will true the axles and polish them.
We will not cut out on the bandsaw, because I am too afraid of my eight year old running it.
We will use a coping saw.
What I learn wd from last year is that we should build two cars. I will build one and show him the steps. He will build the other, step by step with me.
He should learn a lot from this.
Above all, I want the boy to have fun. I don't want it to become a serious exercise.
We will use our best efforts to produce a car that does as well as it can.
Tom Watson - WoodDorker
tjwatson1ATcomcastDOTnet (real email)
http://home.comcast.net/~tjwatson1 /
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Joe wrote:

Joe, Many smart people disagree about whether it is better to have one wheel raised or not. Truth is, you're not very likely to get your axles positioned accurately enough for all 4 wheels to carry weight anyway. Three will be carrying the weight and one will be loafing along. Oh, it will be turning alright, but it won't be carrying much weight. If it touches the track at all, it be a result of the slack between the hub and axle that allows the "high" wheel to drop down to contact the track. The light wheel will also rub along the center rail, so it needs to be treated the same as all the others.
That said, most of the faster cars I ever saw had one wheel raised just a little. You can only raise a wheel on the light end of the car. If you try to raise a wheel on the heavy end, that wheel will just go down anyway and raise the one on the opposite corner.
Find a hard, smooth surface and roll the car to see if it rolls straight or not. If it doesn't, tweak the front axle by bending it slightly fore or aft until the car rolls straight.
DonkeyHody "Give a hungry man a fish and he will eat for a day. Teach him to fish . . . and he will sit in a boat and drink beer all day."
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wrote:

How do you tell the difference between a car with a wheel raised on the light end and one with a wheel raised on the heavy end that settled and raised the light end?
--
LRod

Master Woodbutcher and seasoned termite
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