Bone between two bones expression

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Old 12 December 2009   #1
Bone between two bones expression

Hello!
I'm trying to create an expression to keep the elbow bone right in the middle of the upper arm and forearm bones. (for joint deformation purpose)
How the heck can I setup the expression?

Thank you in advanced for your ideas !!!
 
Old 12 December 2009   #2
I'd use same as item in stead of expressions. They are much easier to work with. Plus it works better with IK.

I made a example scene. I'm not sure if this it's exactly what your looking for. I hope it helps though.
Attached Files
File Type: zip UpperArmDef.zip (2.9 KB, 10 views)
 
Old 12 December 2009   #3
Thanks Castius... but, no, It's not what I had in mind. (thank you all the same for the scene!)
Here are 2 pics.
The elbow bone (shorter in the pics) should be pointing out in the middle of the upper arm and forearm bones. I'd like to make an expression for this, like taking the angle :upperArm/ ForeArm and dividing It by two. I tried several things but It doesn't seems to work so far.
Attached Images
File Type: jpg Elbow_Rest.jpg (7.0 KB, 6 views)
File Type: jpg Elbow_2.jpg (9.1 KB, 10 views)
 
Old 12 December 2009   #4
Use some expressions with center .See attach

Chris
Attached Files
File Type: zip test_bone.zip (2.4 KB, 10 views)
 
Old 12 December 2009   #5
That's exactly what I had in mind!!!
Thank you very much!!!
Where could I learn more about expressions? I checked various tuts on the web but It's hard to get into rigging with expressions when you're not familiar with It...
Happy new year's eve!

Marc
 
Old 12 December 2009   #6
Try also this file with ik _See attach
Attached Files
File Type: zip ik_bone.zip (3.2 KB, 11 views)
 
Old 12 December 2009   #7
I kind of figured that is what you wanted. But the way you describe it i decided to give you the harder to do example.

Also make sure you using joint compensation. This is basically the same effect but it's just a part of the bones deformation system.

Here is a half rotation using "same as item".
Attached Files
File Type: zip ElbowDef.zip (2.9 KB, 7 views)
 
Old 12 December 2009   #8
Quote:
Originally Posted by lhermittem
Where could I learn more about expressions? I checked various tuts on the web but It's hard to get into rigging with expressions when you're not familiar with It...


www.rebelhill.net
 
Old 12 December 2009   #9
Hey, Chris! That's a very smart use of the center expression in your IK example! I like It a lot! Thanks!
Beast: I'd seen a post a while back in newtek forum about this tutorials set... I think you're right! It looks really complete! I'm going to make myself a little present for christmas!
Thank you!

Castius: thank you for your scenes!
 
Old 12 December 2009   #10
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