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Old 23rd June 2006, 07:33 AM   #1
coldby
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Default spiral spring: am I drawning in a glass of water?

Drawing a spiral coil: before I tryed I was bluntly sure that a few mouse clicks would do it. Now I'm not as sure anymore.
Mind you, not a helicoid, a true spiral: the radius gradually increasing or decreasing, but all on the same plane - the kind of spring you still find in old-fashioned mechanical clocks or toys.
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Old 23rd June 2006, 10:25 AM   #2
Dennis
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Default Re: spiral spring: am I drawning in a glass of water?

I thought there *may* have been a way to do this using Replicator --- I can't see a way to offset the extrusions where they make a spiral, however...

I needed this functionality a while back, and as it wasn't in AC3D already, I ended up getting "Spiralizer":

http://www.armanisoft.ch/webdesign/FrmDownloads.html

Scroll to the bottom section and click that Spiralizer link if you don't understand German.

It exports to DXF, which loads nicely into AC3D. Good workaround until there's a way to do this natively in AC3D...
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Old 23rd June 2006, 11:36 AM   #3
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Default Re: spiral spring: am I drawning in a glass of water?

You could still do it manually by moving the vertices in a helicoid inward while still keeping close to the same plane they were on and keeping an eye on the distance moved display.
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Old 25th June 2006, 08:42 AM   #4
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Default Re: spiral spring: am I drawning in a glass of water?

Thanks folks, mostly for confirming that the Alzheimer hasn't had me yet And, Dennis, thanks for Spiralizer - guess I'll have it downloaded and tested before the Sunday's over.
Anyway I muddled through by applying the old-fashioned trick (from the times of ruler and ink) of drawing a set of concentric circles with decreasing radii, deleting three quarters of each, rotating and assembling together the remaining arcs, drawing (manually!) a path along the vertices and then eventually extruding the cross-section along the latter. Pretty dirty indeed, and it took a helluva time - but the final result really looked like a spiral.
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Old 25th June 2006, 10:16 AM   #5
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Default Re: spiral spring: am I drawning in a glass of water?

One other method worth considering:

To mimic the 2d shape of a spiral in AC3D, I followed the steps from the attached image:

1. I pulled the image of a spiral off the web ( http://images.google.com/images?q=spiral )
2. Loaded the image in the AC3D Front view using Ortho -> Set Background Image, then traced the spiral image using a Line.
3. Subdivided the Line.

The Spiralizer will be better if you're going for more mathematic precision, or for spiraling the spring "upward", but this is probably a faster/easier way to get a basic spiral...
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Old 25th June 2006, 12:22 PM   #6
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Default Re: spiral spring: am I drawning in a glass of water?

Dennis,

Could this be a need for a more "generalization" of your wave plugin?
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Old 25th June 2006, 12:45 PM   #7
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Default Re: spiral spring: am I drawning in a glass of water?

I'm not sure of the math for making a spiral, but it may very well work...

I would love to revisit the Wave plugin for this plus a few other things. It's a little clumsy now because all waveforms are based off of 0,0,0, forcing you to move your geometry there...

I would like to modify it to fix that issue, show a realtime-preview, and shape wavelengths based on the size of the selected geometry (so you can, for example, issue 1 wave, 2 waves, 3.5 waves, etc instead of havng to calculate it out yourself manually).

Perhaps with these changes, I could introduce other waveforms as well, possibly spirals...

I'm in the middle of a few other projects now, but this may be forthcoming later on.
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Old 26th June 2006, 04:10 AM   #8
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Default spiral math

Hi Dennis,
the math of a spiral is as easy as you wish it to be - but in polar coordinates

The simplest one is (rho) = a (theta) [ sorry, can't manage Greek letters here], a docile and tame linear spiral also known as Archimede's.

Then there's the one used by snails, looking like (rho) = exp (k (theta)): the larger the animal, the faster it grows - at least until it meets a hungry Frenchman.

If you want to make the latter more realistic you might as well consider that an element of cross-section has anyway to accommodate only a slice of the animal, thus make it (rho) = exp (k (theta)) ^ (2/3) [one dimension falls off].

However if you want it really complicated and interesting, the only limit is your fantasy. Unless you're married, of course - then the first unobjectionable obstacle would be your wife
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Old 26th June 2006, 04:21 AM   #9
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Default Just slightly off-topic

Speaking of guide-paths for extruding objects, every now and then it would be convenient doing it in parts (as for my fake arc-contrived spiral) and then assembling and merging the paths together before extruding. But AC3D seems not to like it: either a single monolithic path or nothing.
Is there a way to get a single path out of a set of sub-paths?

And, more generally: is there a way to melt permanently a set of several objects into a single one? Apparently merging them won't do: although you may not split them back anymore, AC3D seems to remember even too well that they haven't been born as a single entity.
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Old 26th June 2006, 06:50 AM   #10
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Default Re: spiral spring: am I drawning in a glass of water?

Thanks for the formulae, coldby

There's no way I know to combine multiple line surfaces --- you can get them into one object, even optimize out the dupe vertices, but the only way to convert them to a single line that I know of is a manual process:

1. select your two line segments
2. perform an Object -> Merge
3. ensure two of the vertices where the surfaces meet are in the same location (select them and use Vertex -> Snap Together)
4. perform an Object -> Optimize Vertices to get rid of the dupe vertex
4. select both lines and perform a Surface -> Remove Surface Only. This will leave your vertices intact, but will remove the lines.
5. in Vertex mode, select each vertex one at a time in the order you want them in your final line
6. perform a Vertex -> Create Ordered Surface
7. set the Surface Type to Line using the buttons in the bottom left of the AC3D interface

Would be nice to get a built-in utility to merge lines...
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