Hello brand new here.

Secrets, tips, tools, design considerations, materials, the "science" behind it all, and other topics related to building the cars and semi-trucks.
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Sleestak
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Hello brand new here.

Post by Sleestak » Thu Jan 10, 2019 5:09 pm

Entered a pinewood derby as a kid and my car finished dead last. Dad wasnt around to help. I just cut the front off sanded and painted it. Thats it. My daughter is now in girlscouts and has a derby coming up and we are going to win 1st place at any $ cost! I found this forum and watched youtube videos. Ill use this for my questions.

1. Rules state oil is allowed. My question is should I use oil on a track where most of the other cars will be using graphite? If the car makes several runs I dont want graphite dust getting in my oil
tires. Should I just use graphite?



Sleestak
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Re: Hello brand new here.

Post by Sleestak » Thu Jan 10, 2019 5:12 pm

Which front tire should be in the air? Having only 3 touch the track is allowed but need the 4th tire on the car. By doing this you lower the opposite side tire only with a toothpick? The back tires need no toothpicks?



Sleestak
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Re: Hello brand new here.

Post by Sleestak » Thu Jan 10, 2019 5:26 pm

With all the talk and effort to remove friction I'm stumped why one would want the cars tires to grind against the rail the whole way down to reduce wobble. And does one always want this or does it depend on the type of track? I need alot of work understanding this. To ride a rail do the front tires slant away from the car from the top of the tire like in a V pattern if looking from the front of the car? Or just 1 tire? What about the back? The opposite like an u side down V paterern if viewed from the rear.



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Darin McGrew
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Re: Hello brand new here.

Post by Darin McGrew » Thu Jan 10, 2019 8:25 pm

Sleestak wrote:
Thu Jan 10, 2019 5:26 pm
With all the talk and effort to remove friction I'm stumped why one would want the cars tires to grind against the rail the whole way down to reduce wobble.
Well, for one thing, the goal of rail riding is not to have the wheels "grind against the rail the whole way down".

The goal of rail riding is to avoid bouncing hard against the rail multiple times on the way down. You also end up taking a straight course down the track, rather than taking a slightly longer zig-zag course down the track.

It's a trade-off. You avoid bouncing hard against the rail, but that doesn't mean that you ignore friction. So you want only one wheel touching the rail (the dominant front wheel) and the others never touch the rail (the rear wheels, and the raised front wheel). And you want as little weight on that one wheel as possible, so the center of mass of the car should be as far back as possible while still remaining stable (and moving the center of mass back has other advantages anyway). And you want to touch the rail as lightly as possible with that one wheel, so you align it to steer as little as possible while still consistently riding the rail.

But with that said, rail riding is not a basic technique. It's the kind of thing that you do after you've got all the basic things under control.



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Re: Hello brand new here.

Post by Speedster » Thu Jan 10, 2019 9:43 pm

Hi there, Sleestak. Welcome to Derby talk.
Here are your answers:
1. No
2. It doesn't matter
3. one always wants this

OK, I'm kidding around with you. One nice thing is Money is no object. That's going to help. Since you are interested in speed my eyes lit up. Remember, this is your daughters car and you want to be sure she has lots of Fun with the experience.
Please check your email



Sleestak
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Re: Hello brand new here.

Post by Sleestak » Thu Jan 10, 2019 10:57 pm

Yes its.my daughter car. She is 5 years old. She is going to pick the car color and tire color and the sticker and if she wants her name on it and pick the number and name her car but that is about all she is physically able to do.



Sleestak
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Re: Hello brand new here.

Post by Sleestak » Thu Jan 10, 2019 10:58 pm

Speedster wrote:
Thu Jan 10, 2019 9:43 pm
Hi there, Sleestak. Welcome to Derby talk.
Here are your answers:
1. No
2. It doesn't matter
3. one always wants this

OK, I'm kidding around with you. One nice thing is Money is no object. That's going to help. Since you are interested in speed my eyes lit up. Remember, this is your daughters car and you want to be sure she has lots of Fun with the experience.
Please check your email
??? No dont use oil? Or were you saying no to graphite?
Last edited by Sleestak on Fri Jan 11, 2019 6:45 am, edited 1 time in total.



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Darin McGrew
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Re: Hello brand new here.

Post by Darin McGrew » Fri Jan 11, 2019 12:28 am

Sleestak wrote:
Thu Jan 10, 2019 5:09 pm
1. Rules state oil is allowed. My question is should I use oil on a track where most of the other cars will be using graphite? If the car makes several runs I dont want graphite dust getting in my oil tires. Should I just use graphite?
My experience is that most cars use whatever is provided at the workshops. So I bought Krytox and started providing it at our workshops instead of graphite. That eliminated the black mess from the graphite.

I don't know what to do with all the graphite that is sitting unused in a box in the church attic though...



Sleestak
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Re: Hello brand new here.

Post by Sleestak » Fri Jan 11, 2019 5:43 am

Darin McGrew wrote:
Fri Jan 11, 2019 12:28 am
Sleestak wrote:
Thu Jan 10, 2019 5:09 pm
1. Rules state oil is allowed. My question is should I use oil on a track where most of the other cars will be using graphite? If the car makes several runs I dont want graphite dust getting in my oil tires. Should I just use graphite?
My experience is that most cars use whatever is provided at the workshops. So I bought Krytox and started providing it at our workshops instead of graphite. That eliminated the black mess from the graphite.

I don't know what to do with all the graphite that is sitting unused in a box in the church attic though...
My question is.......should I use oil at a derby most everyother car is full of graphite? I hear mixing the 2 is a big no no. I except the track to have some dust on it.



Sleestak
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Re: Hello brand new here.

Post by Sleestak » Fri Jan 11, 2019 6:39 am

Image

Trying this....thats the car Im ready to purchase. Yes its not flat as a skateboard or looks like a pencil but being for a 5 year old it has to resemble a car. She isnt gonna have fun with a hollowed out pencil shaped car with a big oval weight on the back.

And the pic didnt work.



Sleestak
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Re: Hello brand new here.

Post by Sleestak » Fri Jan 11, 2019 7:04 am

This is personal for me to win this thing not take 3rd or 2nd but win. I want my daughter lifting the trophy. Lol. That said it will be ok to lose as long as we enter the best prepared car we can. Maybe all the other dads put in the same effort. Its personal due to how terrible my cars performed when I was 8. I still remember my car. Rounded front and back is what I could do with grampas hand held wood saw. I painted 1 coat of gold paint and stuck a 10 on the front even through could hardly tell which was the front. Mom melted fishing lures or car tire weights we found on the ground behind the service station and poured the melted lead into the car center bottom. In them days the track was maybe 5o feet atleast. It didnt start as steep as the tracks I see on youtube. My car was beated by as much as 8 feet maybe more. All the kids with Dads did much better. I had a dad but he lived in Flodia and us in Minnesota.



Speedster
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Re: Hello brand new here.

Post by Speedster » Fri Jan 11, 2019 9:19 am

God Bless your Mother.



Sleestak
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Re: Hello brand new here.

Post by Sleestak » Fri Jan 11, 2019 9:55 am

Speedster wrote:
Fri Jan 11, 2019 9:19 am
God Bless your Mother.
She raised 4 boys on a part time bus drivers salary. Safe to say we were not wealthy.



Sleestak
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Re: Hello brand new here.

Post by Sleestak » Fri Jan 11, 2019 9:58 am

Question. What is the single ONE most thing a guy can do that affects the speed of the car?

Or is someone wants to rank them that would be great.



Speedster
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Re: Hello brand new here.

Post by Speedster » Fri Jan 11, 2019 10:24 am

Take your book by Dr. John D. Jobe, The Physics of the Pinewood Derby, with Engineering Applications, and bury it in your back yard.
Quit "clicking" on Derby talk.
Maybe I should Reverse that.

There is no ONE most important thing. If what you are saying is wanting to win 1st place, then the second you try to break the Laws of Physics, You Lose.
I know that's Harsh, but that's the way it is.

Tim, are you just trying to find out if I'm telling you the truth?



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