Seeking info, calculating

General cubmobile related topics.
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sporty
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Seeking info, calculating

Post by sporty » Sun Dec 18, 2005 12:01 pm

Some of you are regs in the pinewood derby section.

I was hoping that 1 of you may have some thougths, answers.

if you have a 4 foot ramp, that angles down about 16 feet (best guess may be less). then flattens for 150 feet.

What would be the best placement for the seat ?

Since no weight can be added, only using the driver and the seat placement.

Going with the standard dimensions for a cub mobile. with 12 inch wheels.


Where would the best place be to place the seat/driver ? 1 foot from the rear axle ?


sporty



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Re: Seeking info, calculating

Post by Teeeman » Mon Dec 19, 2005 3:14 pm

The more rearward you can place the seat, the more potential energy you have at the starting line (just like Pinewood).

Dead center (left/right) is best for stability.


We had an offset (to the left) seat on ours as our event was only straight line and we were carrying a front wheel to reduce steering scrub.


-Terry


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Da Graphite Kid
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Re: Seeking info, calculating

Post by Da Graphite Kid » Wed Dec 21, 2005 9:30 am

I agree with Teeeman; the more rearwards your cm the more potential energy you should have. Where this is on a Cubmobile is anyone's guess as unlike in a pinewood derby car where everyone uses a pinewood block to build the body and frame from; everyone may not have to use the same wood or materials to build their Cubmoblie. So you will end up with Cubmobiles that have different overall weight and weight distribution. All that said I think that the best distance is the same for a pwd car: as far rearward as you can go without making the front end unstable.

If your son is the only driver; make your own test ramp and move the seat back until the front end becomes unstable (just don't hurt him in the process!).


Da Graphite Kid



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Stan Pope
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Re: Seeking info, calculating

Post by Stan Pope » Wed Dec 21, 2005 10:45 am

You should be able to make the final seat placement by weighing all components ... parts and driver, and then laying them out with front wheels (or front axle) supported on a scale and rear supported on rear wheels or pivot at rear axle. This saves on pencil lead and brain cells as compared to trying to do it computationally.

The hard part will be trying to get the driver into his "racing pose" when the parts are loose!


Stan
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sporty
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Re: Seeking info, calculating

Post by sporty » Wed Dec 21, 2005 1:25 pm

Thanks all.

I have some new materials and design in mind this year. Sme of which I have already gotten.

I would like to post for everyone, But at the same time. I dont want to end up seeing someone race my son with getting the info from here.

Theres planty of info out there and stuff to buy for a pinewood derby car.

Not so much on the cubmobile.

The last couple of years the rules have stated only pine wood. 2x4 or 2x6.

But I have a combination in mind.

I will send you a e-mail stan. See what you think.


Sporty



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Re: Seeking info, calculating

Post by Teeeman » Sun Dec 25, 2005 9:46 pm

An extremely simple way to find the front/rear CG is to balance the car on a 2X4 (with scout on it, of course being careful).

This will provide a front/rear eastimate.

Stan's way works too, just requires more hardware :)

-Terry


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Re: Seeking info, calculating

Post by Smell of pine » Thu Feb 16, 2006 11:13 pm

Why can't you lean the seat back so that the feet can still reach? That way you get more rear weight.



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