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Author Topic: Folding paper around a drum  (Read 271 times)

AlecJames

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Folding paper around a drum
« on: September 18, 2017, 11:30:05 am »

I want to animate a sheet of paper going through a mechanism - like a sheet going through a printer.  I'm trying different methods and I'm stuck on an issue that I've hit a few times -

I've made a mesh 78x0.5x156 (12x 16z divisions) and I want to rig it with a string of 12 bones.  I want each bone to influence a strip across the width of the paper. 

When I choose bone influences the influence zone is set by a tube - I cant flatten the tube to influence the strip of paper (- am I correct or is there a way?)

So I use painted weights.  I need each bone influence to be painted across the width of the note.  This is where I struggle, I need a steady hand to paint a straight stripe and a keen eye to tell when the strip for each bone is not 100% influence - otherwise when I move the bone position the paper distorts because other bones still have a small influence.  (I use influence 1.0 with a brush smaller than a face) By trial and error I get a better results but is there an easy way? (e.g. It occurred to me that if I understood the weights syntax in the anim8or file I could edit it to get the desired strips)

Is there an easier way?

When I paint weights, is if affecting the points or the faces?  What I mean is for best results, should I be trying to paint stripes on the centre of the faces or along the edge points?
thanks

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johnar

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Re: Folding paper around a drum
« Reply #1 on: September 18, 2017, 12:14:58 pm »


Only points are influenced directly by weight painting and also bone influences, so the idea is to paint the points. (or enclose the points within the influence 'tube')
 If i'm understanding you correctly, the rigging method you've described should work.
 If you're still having distortion problems, it may just be a matter of creating more seams with more bones.
It'll be interesting to see how it goes.
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ENSONIQ5

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Re: Folding paper around a drum
« Reply #2 on: September 18, 2017, 12:56:38 pm »

Having done something similar a long time ago (folding a paper plane) your method is correct, and about the only way to do it within Anim8or (though editing the AN8 file directly isn't a bad idea at all, once you've worked out what's going on).  Weight painting is the best place to start, make sure your 'paintbrush' is small enough that you can accurately target individual points without touching adjacent points.  I would also suggest using a coarse mesh with 15 faces ('strips'), to align with each bone joint, before converting to a subdivision.  It will be a bit painstaking however you do it and it may require a bit of experimentation to get right, but I'm also keen to see how you go.
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AlecJames

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Re: Folding paper around a drum
« Reply #3 on: September 18, 2017, 01:47:47 pm »

Thanks johnar and Ensoniq5

I tried again earlier with a large weight brush, influence 1.  Starting from the right (my paper is portrait, strips are up/down) I weighted the whole object with the right hand bone, then moved to the next bone and again painted everything to the left.  Now I know just to target the points I run the brush up and down vertically with the edge of the brush over the centre of the faces.  Because the whole left area is the same colour I'm finding it easier to spot bits that I miss.

I did a quick test by setting each bone to 5 degrees (in a test scene) and the result was a smooth curved sheet :)

I'm using 1.00b 1296
In figure mode when I'm setting the bones free or locked, if I set an axis to locked it is not remembered if I OK and then reopen the dialog.  Is that a bug?
If I check locked before unchecking free, when I uncheck free, the check is cleared from locked as well. Is that a bug?
Are free and locked mutually exclusive options or is there some special meaning if they are both unchecked or both checked?

I will continue working on it this evening.  I'll post my test results.
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AlecJames

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Re: Folding paper around a drum
« Reply #4 on: September 18, 2017, 10:21:03 pm »



My first test render.  The paper has 12 bones up the middle.  I made 2 sequences, one bends the paper clockwise around the top roller, the other bends it ACW around the bottom roller.  This was not easy, I had to key almost every frame (18 in each bend) for all 12 bones - took ages.

The test render is slower and much closer than the intended presentation so I'm happy with the result.  I'd like a faster method, the sequences are for 50mm rollers, if I needed another diameter or a different wrap angle I'd need a new sequence.  Although I could build a library...
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johnar

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Re: Folding paper around a drum
« Reply #5 on: September 19, 2017, 09:07:25 am »

Well done Alec. Looking good.

 
Quote
Although I could build a library...
..... You'll never regret it.
 The small effort it takes to export a sequence can repay itself over and over and over again.
 IN my 'IMPORT' folder  theres a folder 'FIGURES' and a folder 'OBJECTS' and a folder 'SEQUENCES'.
Even if you keep all files relevant to a project within the relevant project folder, it's also a good idea keeping a seperate copy of every FIGURE, every OBJECT and every SEQUENCE, within those 'figure, object and sequence' folders  (the same as textures) 
Lets face it, over time projects can get lost, corrupted or whatever. Many times i've been saved a ton of work, thanks to a saved figure and a bunch of saved sequences to match.

 A sequence library?......Absolutley 100% a good idea.  ;)
« Last Edit: September 19, 2017, 09:10:38 am by johnar »
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kreator

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Re: Folding paper around a drum
« Reply #6 on: September 19, 2017, 09:32:39 am »

Well done Alec. Looking good.

 
Quote
Although I could build a library...
..... You'll never regret it.
 The small effort it takes to export a sequence can repay itself over and over and over again.
 IN my 'IMPORT' folder  theres a folder 'FIGURES' and a folder 'OBJECTS' and a folder 'SEQUENCES'.
Even if you keep all files relevant to a project within the relevant project folder, it's also a good idea keeping a seperate copy of every FIGURE, every OBJECT and every SEQUENCE, within those 'figure, object and sequence' folders  (the same as textures) 
Lets face it, over time projects can get lost, corrupted or whatever. Many times i've been saved a ton of work, thanks to a saved figure and a bunch of saved sequences to match.

 A sequence library?......Absolutley 100% a good idea.  ;)


Something I always do nowadays, I have Libraries of all my stuff going back to when I first started using anim8or way back in the early 2000s
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