Saturday, September 21, 2013

The Cold Equations

Lord Kelvin once said:

"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be."

Numbers are a tool.  They are a way of characterizing a thing or effect or event in a form that can be manipulated and translated usefully.   Doing the numbers is the only proper way to do engineering.  And even a quick-and-dirty order-of-magnitude is an invaluable tool for figuring out basic problems.

Even if (or, perhaps, especially if) the numbers reveal a painful truth.

I have been tasked with creating a printable 3D model of a Cadillac Gage Commando (an armored car).  I scanned and cropped the reference materials, started reading about variations in hull shape and accessories.  And refreshed my memory on the Design Rules for the "Fine Detail" (objet printer) material at Shapeways.

To within a power of 2, that particular printer is as detailed as an extrusion-molded plastic model kit.

A quick calculation show that at the intended scale of the final model (1/56) I could represent surface details as fine as 1.2 cm, with extrusions as fine as 5.6 cm.  Which is almost fine enough to represent individual grab bars to scale.

Even using conservative values, I appear to be obligated to make an effort at detailing headlight assemblies, vision blocks, gun ports, hinges on the hatches, etc.  So this model is going to take a while.

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