David,
It's a simple work around, but in answer to your original question why
not set up the hierarchy as follows:
------------------------------------------------------------------------
-
Null (determines the pivot point) another optional child null can be
placed under here to use as a visual guide for translation of Null3.
------------------------------------------------------------------------
-
Null2 (parent) /\ separate hierarchy, position constrained to Null
-> Null3 (child)
------------------------------------------------------------------------
-
Null and Null2 share the same translation
The idea of this setup is that Null3 (local posy) will be the child that
drives the rotz of Null.
You can link the rotation of Null (rotz) as before with simple drag and
drop (I found multiplying by 16 in the expression seems to get the
rotation angle more or less right in relation to the translation of
null3).
I tend to use a bit of old school trig for that sort of thing, meaning
the translation in y would match up to the angle of rotation angle in z
if using arctan.
Yes it uses more nulls but it's a solid work around which avoids cycles.
Null and Null2 would then be children of the head bone if you are using
it for a jaw.
I hope that helps a bit and apologies if it's not what you were looking
for.
Morgan
Character TD Passion Pictures
-----Original Message-----
From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On Behalf
Of David Gallagher
Sent: 28 February 2006 15:11
To: XSI(at)Softimage.COM
Subject: rigging dilemma: driving a parent with attributes of the child
In Maya, I have no problem making two parented nulls and making the
parent's rotation dependant on the child's translation. So as you (for
instance) translate the child down in y, the parent can rotate the child
in x.
This same setup creates a dependancy cycle in xsi. There's probably some
other way to this, but I can't figure it out.
The situation is a jaw that's translating down, but needs to rotate as
well from a high pivot as it opens when the neck is at some poses.
Thanks,
--
David Gallagher
Animator, Blue Sky Studios
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