CGTalk - Shoulder / XSI

IZZE

07-23-2009, 09:03 PM

Hello everyone. I was watching the FK Arm Setup #009 podcast by Lucas Martell, and was intrigued by his shoulder / arm setup. I am having difficulty trying to figure out how to implement this kind of setup with the standard biped rig. (when the elbow gets to a certain height, the shoulder starts to move up) When I get everything setup the way I think it should, my upper arm root will no longer follow my shoulder bone eff. I am pretty sure I understand why.... but think this should be possible somehow.
http://www.christopher-mccabe.com/forums/arm_rig.jpg

Just to illustrate my steps,
1. Draw shoulder bone. Draw arm chain and parent arm root to shoulder eff.
2. place null at elbow location and parent null to body.
3. Place second null in same location as first and parent it to first (to zero out translation of second null)
4. Link rotation of shoulder bone to translation of second null.
5. Constrain position of second null to lower arm bone.

It would be really swell if someone has any ideas on a better way of doing this. I already have a character rigged with biped, so I would like to stick with it instead of building a new custom rig. I have tried several setups, but keep getting stuck in a cycle dependency. I have a quick scene setup if someone has the time to look at it. Thanks a ton! Arm Rig Scene (http://www.christopher-mccabe.com/forums/Arm_Rig.scn)
Poscast = http://www.pigeonimpossible.com/podcast/

mrxzof

07-24-2009, 10:19 PM

It's probably the "parenting" of the arm bones to the shoulder effector. This way makes some issues. So you should make a pose constrain instead. I've just test it, it works ! A cool trick !

IZZE

07-25-2009, 12:04 AM

Hmmm. I would love to see your scene. I got the arm root to follow the shoulder effector, but when the wrist gets two far away from the shoulder, I get a shuddering in the chain (dependency cycle). Plus the arm bone does not follow the shoulder when I set some keys on the wrist and playblast the timeline.

IZZE

07-25-2009, 02:19 AM

I think I might have found a solution using a Pseudo-Root. But it would still be cool to see your scene file. My Scene (http://christopher-mccabe.com/forums/Arm_Rig5.scn)

monkey1988

08-06-2009, 01:04 AM

would you be able to post up a set by step of your finished technique as im VERY new to rigging but feel that this would be a great asset to my characters setup.

i downloaded your final rig setup but i can't work out how you did it and i tried to follow your steps above but they confused me as well when you started talking about linking rotation.

so if you could post up a step by step that would be great, thank you. im using XSI 6.5

thank you

IZZE

08-06-2009, 04:09 PM

Hello.
Well, I am still having some small problems with the IK setup so It will probably be a waste of your time to explain a rig that does not work properly. But you can look at the podcast link in my first post to see how Lucas Martell completed his setup using FK. While attending Siggraph, I thought I would run this problem by the Softimage representative. He was very helpful and I hope there might be a solution to my problem. This setup keeps running into cycled dependency issues, but I still wonder why the upper arm root does not follow the shoulder effector after using link with.

The linking rotation is setup by selecting the shoulder bone, hitting Ctrl+K, Right clicking on the rotation axis and selecting Link With. Then selecting the null you wish to use to drive the rotation of the shoulder bone. And link it's position Y to the rotation z of the shoulder bone.

monkey1988

08-07-2009, 04:31 PM

thanks for getting back to me, i just wanted to say that i downloaded your scn and tested it out and it seemed to be working 100%, i had to add an up vector do that the arms would act naturally but other then doing that it looks like it works perfectly, i enveloped it to a test character and i couldn't see anything wrong with it so could you please explain what the issue is that your having as i just can't see it.

IZZE

08-08-2009, 05:52 PM

I would like to add this setup to an existing biped rig. The biped rig uses a one bone chain for the shoulder and a two bone chain for the arm. As you can see in the illustration in my first post, after linking the shoulder roation to the null position, the upper arm root no longer follows the shoulder eff. Example HERE (http://www.christopher-mccabe.com/forums/Arm_Rig.scn)

My solution uses a three bone chain with a Pseudo-Root. Which is not the same as the biped rig.

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