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Author Topic: Need formula for finding "scale weight" to match scale size  (Read 7777 times)
W8JJI
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Posts: 291




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« on: February 22, 2011, 04:05:04 PM »

You know those plastic model car kits that you put together that are 1/25 scale ?

At 1/25 scale the average car ends up being about 3 and 1/2 inches wide and 8 and 1/2 inches in length.

So what would the correct "scale weight" be for a 1/25 scale model that in real-life would weigh about 3750 pounds ?

Dividing 3,750 by 25 gets 150 pounds, that just doesn't seem right.

So, how do we figure this out ? 

What should a proper scale weight for a 1/25 scale model car be ?

Thanks


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W5FYI
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« Reply #1 on: February 22, 2011, 08:49:53 PM »

In reducing size to scale, you should keep density the same. Density is mass per unit volume, so you need to know average height as well. Divide the actual car's weight by its length x width x average height and you get density. Multiply that number by the model's length x width x average height and you should get the scale weight.

Using the figures you provided, and guessing the average height of the model is 2 inches, then your life-sized car would have a volume of around a million cubic inches (930,000 cu in). Divide the actual weight, 3750 pounds, by 930,000 and you find the density is about .004 pounds per cubic inch. Now, calculate the volume of your scale car; 8.5 x 3.5 x 2, or 59.5 cu in, and multiply that times .004, and you should get .24 pounds, about a quarter of a pound, for the scale weight. Does that seem more reasonable?
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G3RZP
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« Reply #2 on: February 23, 2011, 12:13:25 AM »

I went a different route. The volume is 1/(25cubed) or 0.64 times 10-6. Mutliply that by 3750 and you get - low and behold! - 0.24 pounds.....same as W5FYI. Of course, it assumes the same avaerage density throughout the model as the original.
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KE4JOY
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« Reply #3 on: February 23, 2011, 08:31:57 AM »

Huh... wonder what he is up too  Huh
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AB3MO
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« Reply #4 on: February 24, 2011, 06:19:08 AM »

Dividing 3750 pounds by the cube of 25 (15625) equals 0.24 pounds (3.84 ounces).  You are scaling the dimensions down by a factor of 25 in all three dimensions, so the weight should be scaled down by 25^3.
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G3RZP
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« Reply #5 on: February 28, 2011, 12:57:31 PM »

At least we all seem to agree on the maths.
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