View Full Version : a really serious rigging problem!

09 September 2006, 11:19 AM
hi all,

i have a rigging problem.

i have the basic character skeleton setup, and on the arm i have the hand bone constrained to a control box that controls the rotation and position of the hand. i am animating IK.

the problem i have is that when i animate the hand and the up vector, sometimes the whole wrist twists like 2000 degrees and screwsup the geo. it also happens when i scrub my animation too fast back and forth. also when i move the upvector a little extreme then if i press ctrl z it does the same thing.

if i go to the kinematics of the hand bone, and i wiggle the values or if i reset the transformation value it jumps back to normal. there are no keys on the bones.

the rotation value of the control box is normal when the hand bone's ( which is orientation constrained to the control box ) value is totally random.

i already asked some advanced XSI users and they didnt seem to know. Please any help would be appreciated ! I use XSI 5.11

09 September 2006, 12:13 PM
Could you explain the exact setup or perhaps provide a .scn file with the problem area of the rig in it? Right now it's all a bit vague.

09 September 2006, 02:12 PM
I had a problem with a leg. When i was setting actions that inverted the way the leg bends . I fixed it making the initial bend between 2 bones more pronouced.

09 September 2006, 05:28 PM
This behavior might happen whenever you have a cycle dependency loop happening. You might not have gotten a warning about it, but it might be there.
I used to consider it a bug, now I consider it a feature. You just have to do your setup differently.

09 September 2006, 08:32 PM
here is the scn file

and the schematic view if its useful :

09 September 2006, 10:34 PM
Okay, I had a quick tinker, your L_wrist_twist rotation nulls are flipping because of the difference between the L_hand_root and L_hand_bone rotations(your twisting method). The L_hand_root is rotating at somepoint in some poses, causing the rotation of the L_hand_bone value to shoot up higher than expected.

This is simply solved by checking "cnscomp" and pose (or just orientation) constraining the L_hand_root to the L_arm_eff. Hope that helps, I've not tested it for long but it seemed to fix the immediate problem.

09 September 2006, 01:02 AM
sorry, i tried that method, didnt seem to work.. i also tried to constrain the hand bone to the arm bone but it doesnt work/ is there maybe any option in xsi to limit the rotation of a bone?

09 September 2006, 08:18 AM
Ah, okay. Well there's definitely some flipping going on in that area. If you set some neutral poses on the hand root null and the arm effector and on the twist nulls, you'll see more clearly what's flipping. For me, it is now the arm effector and the hand bone which are flipping around. I'll have to take another look a bit later if nobody else can tell you what's wrong by then.

09 September 2006, 12:40 PM
I ran into a nasty problem cause by constraints when you rotate the constraining object around more than 180 degrees. There is a thread somewhere around here that goes into more details. Basically, I was able to get around this problem by using Expressions instead of constraints. Problems like these are a big part of why I build my own rigs. I found that the XSI rigs may be nice for simple things, but as soon as you try to do more complicated animations it has a tendancy to have problems and it can sometimes be quicker to build your own rig than fix problems on one of the XSI rigs.

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09 September 2006, 12:40 PM
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