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 How do you create a double helix?
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satman68
Inquisitive

73 Posts

Posted - 12/09/2009 :  15:42:17  Show Profile  Reply with Quote
Hello I am trying to make a double helix, I only need just the tube, see attached.
Can anyone help me, I have tried the lathe tool with no luck.

Thanks very much.



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jpro
A Fountain of Information

USA
4991 Posts

Posted - 12/09/2009 :  15:56:52  Show Profile  Visit jpro's Homepage  Reply with Quote
use the lathe tool with multiple rotations and a vertical sweep.

What have you tried so far with the lathe tool?

Jean
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satman68
Inquisitive

73 Posts

Posted - 12/10/2009 :  03:35:44  Show Profile  Reply with Quote
Thanks Jpro, I am getting there but as you can see the tube becomes flattened. How can I keep the tube consistant all the way through?



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jpro
A Fountain of Information

USA
4991 Posts

Posted - 12/10/2009 :  08:51:58  Show Profile  Visit jpro's Homepage  Reply with Quote
yes, I'm seeing that here, too. What version of Strata are you using?

Jean
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MrChristopher
A Fountain of Information

USA
2220 Posts

Posted - 12/10/2009 :  18:21:18  Show Profile  Send MrChristopher an AOL message  Reply with Quote
I've developed a mechanism for doing this manually. I'll record a tut and post it.

Chris
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Stratagizer
A Regular

USA
441 Posts

Posted - 12/10/2009 :  21:36:28  Show Profile  Reply with Quote
I have had pretty good luck w/double helixes & Strata. The flattening should be fixable in the object properties "scale" settings. Perhaps you used the scale tool to make the helix longer? Remember to experiment with the settings in object properties for getting more/less twists etc.
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jpro
A Fountain of Information

USA
4991 Posts

Posted - 12/11/2009 :  09:04:09  Show Profile  Visit jpro's Homepage  Reply with Quote
I don't think adjusting the scale is going to fix anything. the problem is the orientation of the profile along the spiral, which cannot be changed.

satman, there is one fairly simple way to do this. start with one of the lathe objects you have already created, as in your image above. Export this spiral object as TGS Amapi.

Import that piece into a new file (it will have the extension .x) Set your import options to NURBs as skin, and set the complexity to 1.

After it is in, ungroup it to break the shape (this may not be necessary, just try it to see) Now go at it with the unskin tool (or option-skin if you are using version 6)

Continue unskinning until no surfaces show in flat or shaded mode. Now you have several curves that can be used for a skin path. Choose one to work with, hide or delete the others.

Notice that one end of this spiral curve is probably a little distorted. You can edit it to clean that up.

Now extrude a circle along the path. This will give you one leg. Recenter the origin of that leg, and rotate it 180 along the length of the leg to get the second leg.

If the height is not right, it will probably be better to scale the spiral path up or down before the path extrusion rather than after.

Jean

Edited by - jpro on 12/11/2009 09:22:50
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jpro
A Fountain of Information

USA
4991 Posts

Posted - 12/11/2009 :  09:10:08  Show Profile  Visit jpro's Homepage  Reply with Quote
Here is a related topic; this shows a more recent method, using newer tools and techniques, to derive a similar shape

http://www.stratacafe.com/image.asp?imageID=23003&artistimages=1&killnext=0

Jean
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MrChristopher
A Fountain of Information

USA
2220 Posts

Posted - 12/12/2009 :  15:27:16  Show Profile  Send MrChristopher an AOL message  Reply with Quote
http://web.me.com/mrchristophersea/Spiral.mov

Here's another method of generating a spiral path, albeit a bit more convoluted than the method Jean shows above. It has the added benefit of generating a bezier path that can be used for either bezier path extrusions or re-purposed for polygon object generation.
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jpro
A Fountain of Information

USA
4991 Posts

Posted - 12/12/2009 :  17:34:39  Show Profile  Visit jpro's Homepage  Reply with Quote
that is a bit involved. the Amapi technique is an oldie but goodie, and it gets you a nice bezier, with fewer excess control points.

Could we combine your technique with my second technique to get a clean bezier curve? I think it would be messy...

anyway, we have 3 good techniques; one may be better one time, the other the next.

Jean
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MrChristopher
A Fountain of Information

USA
2220 Posts

Posted - 12/12/2009 :  18:19:27  Show Profile  Send MrChristopher an AOL message  Reply with Quote
yeah, my technique is one that could be used to generate a primitive of sorts which once generated could be used other times.
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