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Old 11-25-2013, 02:56 PM   #1
Laserschwert
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How to model/animate a bellow cover

I'm trying to model an animatable bellow cover, like this:



In my case it only has to move long its "squeezing" axis, but I'm wondering how to best model and rig such a thing? It doesn't necessarily have to work in close ups, but I'd like to keep the rigid parts quite defined with crisp (though rounded) edges that keep their volume, while the flexible parts fold in between them nicely.

Max' own hose primitive is exactly that - primitive - since it doesn't keep the volume of the material (and is probably supposed to be used with connections that don't have rigid parts as a support structure).

Funnily we've just had a similar thread to which I've given a solution, but that one isn't detailed for my current project...

Any ideas?

Last edited by Laserschwert : 11-25-2013 at 03:28 PM.
 
Old 11-25-2013, 05:07 PM   #2
Noren
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Perhaps add the thickness relatively high in the stack parametrically and do your transformations without thickness. The folding part can be easily faked, then.
Could be one object even, though it might be a bit harder to get different values for the two different elements.
 
Old 11-25-2013, 07:00 PM   #3
Laserschwert
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I've already tried chamfering the "thick" edges at the top of the stack, but unfortunately chamfers (both in EditPoly or modifiers like QuadChamfer) scale down when the object is "squeezed" together. So that doesn't really work to create the rigid parts.

Also I've tried stringing together the actual panels under the fabric on a spline as instances, while LinkedXforming the both ends of the spline to helpers. That pretty much works in terms of having the panels evenly spread (they keep their percental positions on the spline). I then SkinWrapped a lowpoly "zigzag" bellow geometry to those panels, and it kinda works for the rigid parts. But folding the fabric between the panels still doesn't work this way.

The difficulty comes from the fact that the fabric doesn't stretch, it only (un)folds, thus the "inset" of the folds between the rigid panels should be scaled depending on the spread. I'm sure this could be scripted, but that would be much too complicated. I think I'll just resort to intersecting the panels with a TurboSmoothed or QuadChamfered bellow geometry.
 
Old 11-25-2013, 11:06 PM   #4
PelDaddy
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Here you go.

Spline, lathed with 4 segments, Chamferred, animated with XForm, Shelled.

Bellows.max

Prevents almost all the pinching of the chamfers.
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Old 11-25-2013, 11:13 PM   #5
PelDaddy
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Put a Turbosmooth on it to smooth it out. Would probably work even better with Quad Chamfer.
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Old 11-26-2013, 03:55 AM   #6
Noren
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Quote:
Originally Posted by Laserschwert
I've already tried chamfering the "thick" edges at the top of the stack, but unfortunately chamfers (both in EditPoly or modifiers like QuadChamfer) scale down when the object is "squeezed" together. So that doesn't really work to create the rigid parts.

Only if you squeeze on object level. Since the transformation is linear, you could also simply set up a morph-target and use reaction manager to link it to the distance between both ends. That way you could set up both extremes exactly like you want them.
 
Old 11-26-2013, 09:21 AM   #7
Laserschwert
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Quote:
Originally Posted by PelDaddy
Here you go.

Spline, lathed with 4 segments, Chamferred, animated with XForm, Shelled.

Bellows.max

Prevents almost all the pinching of the chamfers.

Thanks for the scene Although chamfering is still scaled down with the XForm, so that's still not working

Quote:
Originally Posted by Noren
Only if you squeeze on object level. Since the transformation is linear, you could also simply set up a morph-target and use reaction manager to link it to the distance between both ends. That way you could set up both extremes exactly like you want them.


Yeah, I think the reaction manager is the way to go... I hope it won't break my scene.
 
Old 11-26-2013, 12:46 PM   #8
fferro2
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http://area.autodesk.com/louis_tuto... visualization
Thake a look at the #4 tutorial: IK chain.
The last part talk about an accordion door. Very similar rig to what you are looking for.
Best
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Old 11-26-2013, 01:50 PM   #9
Laserschwert
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Thanks. The folding doors are similar, but not similar enough to be applied here. The bellows aren't flat but need to fold on two axis (and four sides). Also the fabric is covering a row of rigid elements that keep their thickness during folding, so those have to be taken into account as well.

I'll try using the morpher with reaction manager to make this work.
 
Old 11-26-2013, 01:58 PM   #10
fferro2
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this rig is just the base.
You can use any arbitrary path(s) for the rigid elements, following the borders of the section in the photo) , and a skin wrap modifier to fold the fabric conecting them.
Best
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Old 11-26-2013, 03:42 PM   #11
Laserschwert
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Alright, I got it working:



So I've stringed several rectangles together on the spline, one set (with a shell modifier) for the rigid panels and another set for the soft fabric part between the panels. I then used the reaction manager to change the scale of the (brown) inbetween rectangles with an XForm modifier based on how far the dummies (to which I LinkedXFormed the spline ends) are apart.

I've used copys of all those rectangles to build the actual bellow as a simple zig-zag geometry which I then SkinWrapped to the rectangles on the spline. I then added a quad chamfer modifier to the edgeloops of the "folds", which I've also added to the reaction manager, so that the chamfer radius increases with the dummies moving further apart. That way the fabric between the panels gets a soft, wavy form when stretched out, and a sharp crease when pushed together.

This is actually the first time I'v used the reaction manager, and in spite of all the criticism towards its stability, it's still a very cool tool.

Last edited by Laserschwert : 11-26-2013 at 03:52 PM.
 
Old 11-26-2013, 03:47 PM   #12
PelDaddy
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Wow. You thought the slight scaling of the chamfering in my scene was still too much? Looked pretty accurate to like a camera bellows on a large format camera.

Could you post your resulting scene. I would like to have a look.

This could also likely be done easily with RailClone.
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Old 11-26-2013, 04:09 PM   #13
Laserschwert
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Here you go: https://www.dropbox.com/s/2hyozmabuffda7e/bellow.max

(it uses the QuadChamfer modifier)
 
Old 11-26-2013, 04:31 PM   #14
PelDaddy
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Very cool. A lot more setup, but for an extreme closeup or something that would be nice. Thanks for sharing.
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Old 11-26-2013, 04:41 PM   #15
Laserschwert
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I've noticed one of my explanations was wrong: I didn't link the reaction manager parameters to the distance between the two dummies (is that even possible?), but to the x-position of the left dummy. Distance would be MUCH better though... how can that be done?
 
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