Noob rigger needs help

Support Animation and Rigging
#1

Looking for a clean way to fix this…

See also WIP thread at

http://blenderartists.org/forum/showthread.php?t=135016

I have a problem with this guys knees. See attached pic’.

They flex ‘at the back’ so the hinge point isn’t in line with the ‘thigh’ bones or shin
bones. Added to that is the fact that ‘extensible’ legs means I have to position the
knees and feet separately, hence the knee ‘effector’

I sort of solved it by using two small knee bones and 'Copy Rotation’s as shown.

But this results in ‘Cycle detected’ warnings on the Blender console, and
some minor issues updating the model after a pose (probably cause and effect
right?).

I’m assuming the ‘Cycle Detected’ messages are something I need to fix.

Anyone know an easy way to fix such a joint? I feel sure I’m missing something
obvious here.

Thanks in advance. G.

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BlenderHelp.jpg800×572 68.2 KB

#2

Cycle detected is something you should take a look at, but it may not need fixing.

If your rig “dances” when you move a bone in the cycle detected chain, then you need to fix it.

Seems like any constraints, parenting, etc that reference any bone earlier in a chain of bones will trigger a cycle detected warning, but the only cycles you need to worry about are those where bones actually move all the way around the cycle. Some constraints fix a bone root or tip in a particular place, and even though they are technically cycles, don’t cause problems with the rig.

#3

Thanks for the advice Orinoco. I didn’t get any useful hits when I ran a search here on ‘Cycle detected’. I think I do have a problem here, in pose mode parts of the mesh can get left behind, they’ll usually snap back in place when I adjust the view. Not sure if that’ll affect animation, but I suspect it will. Guess I can try a quick anim’ test to see what happens.

#4

OK. For the benefit of any other rigging students that stumble across this thread, here’s my attempt to explain the solution… I dropped the copy rotation constraint on the parent bone, locked the rotation of the child bone and used a simple IK constraint on the child bone with a chainlen of 2 to include the parent. That results in a child bone that doesn’t quite point in the right direction (because the parent in included), but that can be fixed by using ‘tree IK’. You add an offset bone to the back of the same parent, set the same IK constraint on it (with the same locked rotations. The IK engine now tries to make both bones point to the target, adjust the offset bone till the angle is right. (There’s probably a name for that kind of offset bone) My joint ended up as attached. G.

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