Geetting COM Under 1/2" ???

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Geetting COM Under 1/2" ???

Post by Topspin.D » Sat Mar 23, 2013 11:58 pm

Does anyone have a design they would be willing to share where the car has a COM at or under 1/2"?

Photos or descriptions of weighting set up are appreciated.

We would like to try a really aggressive car at the district open race.

I should note we'd like to do this with standard wheel base and 4 wheels on the car. Long nose is ok.



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Stan Pope
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Re: Geetting COM Under 1/2" ???

Post by Stan Pope » Sun Mar 24, 2013 12:31 am

Body 1/4" thick. 2 oz 1/4" tungsten cubes 1/8" - 5/8" behind rear axle center. 2 oz 1/4" tungssten cubes 1/8"-5/8" ahead of rear axle center (rear axles in a section of wood 1/4"X1/4"). Thin/remove wood from body until weight with tungsten, body, glue for tungsten, axles, wheels approx 4.8 oz. (CM loc at this point is about 3/8" for your wheelbase. Add 0.2 oz flat trim weight to body to adjust CM location for best time. (The smaller CM location, the greater must be the toe-in on DFW, so there is a trade-off related to track length. Longer track wants smaller toe-in for best time.)


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Re: Geetting COM Under 1/2" ???

Post by Topspin.D » Tue Jan 27, 2015 12:18 am

Thank you Stan!



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Re: Geetting COM Under 1/2" ???

Post by ngyoung » Tue Jan 27, 2015 7:49 am

I do it all the time. Usually i end up sliding my weights forward to get over .5"

I havent been very stable though going that aggressive. This build ended up around there. Cut a ladder body filled voids with Greatstuff. Cut the block to 5/8" then sandeddown till i saw daylight through the wood over the weight pocket the sloped the nose at the front axle hole.
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Re: Geetting COM Under 1/2" ???

Post by Scrollsawer » Tue Jan 27, 2015 9:25 am

Stan's and Ngyoung's comments are pretty much what I do. Twelve 1/4 cubes behind the rear axle when axles holes are drilled 5/8" from the rear of the car body. Total weight of wood, wheels, glue, axles, paint, lube, decorations' clear coat should be at or very near 1 ounce in weight. 24 tungsten cubes, or close to it, should represent the remainder of the 4 ounces of weight. 13-14 (or 13 plus tungsten putty trim weight) placed where Stan mentioned in front of the rear axles is key. This is much easier for me using a ladder design or a Sporty spoon design. Don't forget the importance of taking a precise scale to a scout shop and weighing as many unopened Derby kits as needed to get a couple of kits that weigh a lot less than all the others. This will give you a head start when trying to cut weight down on the car body.

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Re: Geetting COM Under 1/2" ???

Post by Noskills » Wed Jan 28, 2015 5:47 pm

Dave,ditto. You need a super light car. We did not quite get there. Had COM of 0.5 with 23 cubes and putty. With lighter wheels I have gotten 24 cubes and a COM of 3/8th but that was not a scout car. You should be able to make a light enough sporty spoon, I have seen you do it.
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Re: Geetting COM Under 1/2" ???

Post by Topspin.D » Wed Jan 28, 2015 10:24 pm

Thanks guys... I'm going a standard base car. This string was from about 2 years ago when I did that "Stanford" fender car. We're giving it another shot this year (with Spoons in reserve in case it doesn't work out).

But like I said... last standard base cars weren't so good - I should qualify that.... good enough for winning our pack but not even close for district.

We have a test track now so I'll play around with moving the weight around... was just hoping you could give some advanced tips and shortcut the development process for us.



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Re: Geetting COM Under 1/2" ???

Post by Vitamin K » Wed Jan 28, 2015 11:12 pm

Scrollsawer wrote:Don't forget the importance of taking a precise scale to a scout shop and weighing as many unopened Derby kits as needed to get a couple of kits that weigh a lot less than all the others. This will give you a head start when trying to cut weight down on the car body.
This forever tickles me. I know it's perfectly reasonable, given the vast variances in wood density, but still...

*stands up at meeting* "Hi, I'm Chuck. This is my first time at a Pineheads' Anonymous Meeting."

(everybody else) "Hi Chuck!"

"Thanks. So, my story started the same as so many others. My kid was in cub scouts...we did the derby and...I just got really interested you know? It was pretty tame at first...browsing internet forums, buying new tools now and again...but next thing you know I'm sitting in the floor of the scout store, pocket scale out, boxes all around me, and I'm weighing them in turn while this scout and his mom look on in bewilderment..."

:mrgreen: :mrgreen: :mrgreen:



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Re: Geetting COM Under 1/2" ???

Post by Scrollsawer » Wed Jan 28, 2015 11:35 pm

Vitamin K,

The first step to recovery is admitting you have a problem. :paperbag: :idk:

Other than the upcoming Mid-America, Team Scrollsawer is officially retired. We are bridging to Boy Scouts this year. I'm sure there will be a 12 step program in my future. :eek:

Oh wait...our neighbor's kid is a wolf cub, and his dad doesn't have any tools or know the tricks of the trade. Hmmm..... :thinking:

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Re: Geetting COM Under 1/2" ???

Post by ngyoung » Thu Jan 29, 2015 10:35 am

Oh come on Scrollsawer. Feed your habit with some league racing!



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Re: Geetting COM Under 1/2" ???

Post by LightninBoy » Thu Jan 29, 2015 1:31 pm

ngyoung wrote:Oh come on Scrollsawer. Feed your habit with some league racing!

:bigups:



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Re: Geetting COM Under 1/2" ???

Post by gpraceman » Thu Jan 29, 2015 2:39 pm

Guys, let's please keep this forum about the kid's races.


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Awana Grand Prix and Pinewood Derby racing - Where a child, an adult and a small block of wood combine for a lot of fun and memories.

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Re: Geetting COM Under 1/2" ???

Post by Topspin.D » Thu Jan 29, 2015 3:33 pm

Vitamin K wrote: but next thing you know I'm sitting in the floor of the scout store, pocket scale out, boxes all around me, and I'm weighing them in turn while this scout and his mom look on in bewilderment..."

:mrgreen: :mrgreen: :mrgreen:
Been there too. What's wrong with that? :oops:

I think I asked them to bring another box out of the back when I couldn't find enough "acceptable" kits on the shelf....



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Re: Geetting COM Under 1/2" ???

Post by Scrollsawer » Thu Jan 29, 2015 9:33 pm

Topspin.D wrote:
Vitamin K wrote: but next thing you know I'm sitting in the floor of the scout store, pocket scale out, boxes all around me, and I'm weighing them in turn while this scout and his mom look on in bewilderment..."

:mrgreen: :mrgreen: :mrgreen:
Been there too. What's wrong with that? :oops:

I think I asked them to bring another box out of the back when I couldn't find enough "acceptable" kits on the shelf....
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Re: Geetting COM Under 1/2" ???

Post by Noskills » Fri Jan 30, 2015 5:13 pm

This year I bought 2 cases of cars for the pack...happy day having those in the privacy of my our garage for a few weeks. :bigups:
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