View Full Version : stop dynamic IK spline from twisting?

05 May 2008, 10:36 PM
i'm starting to regret not figuring out nCloth soon enough, but i'm so close to finishing this that there is only thing holding me back...

the dynamic IK spline is twisting the geometry (rolling actually) -- how can I stop it from doing this? or at least constrain it so that it always faces a consistent direction?

05 May 2008, 11:08 PM
check out the "Advanced Twist Controls" in the Attribute editor,


05 May 2008, 04:25 AM
thanks john homer for all your replies, hope you aren't sick of me just yet :D

i already tried experimenting with the "advanced twist controls" -- all they seem to do is exactly what they imply, which is, twist my geometry along the IK chain (like ringing out a towel to dry)

so far only the "roll" attribute seems to give me a sense of control over this, but it only allows me to try and key counter-rolls to correct my geometry -- which doesn't solve the problem unfortunately.

here's a playblast of the problem: (

EDIT: unfortunately the playblast is playing at double speed, but hopefully you can still see the rolling effect of the geometry.

05 May 2008, 05:12 AM
you should use "object" as an up vector.. you can probably use the head joint.

I havent used IK in a while as I'm a full-time cloth monkey these days.. but I know when Advanced Twist Controls was first introduced it only worked if the down axis was x (I think it was x...) this was not documented... surley its fixed by now... but you might wat to check that as I know it can give the results you want.


05 May 2008, 06:17 PM
if by fixed, they simply removed X, then yes, it was definitely fixed ;)

Selecting object up and assigning the head joint seems to have eliminated the unwanted rolling effect, and adjusting the "roll" attribute to correct the geometry's position has completely solved my problem.

also, depending on the object, sometimes I choose neg. Z, sometimes pos. Z -- but ultimately I don't think it matters, as long as it doesn't end up twisted, since I can just use the roll attribute to finalize the correction.

once again, thank you for your help.

EDIT: just wanted to point out that the geometry always moves a little or changes its shape slightly when I apply the advanced twist controls, but this is a minor problem -- one that I can likely get away with it.

also that a couple pieces don't want to cooperate, but i'm going to keep playing with different settings -- at the very least i feel like i'm finally moving forward :thumbsup:

EDIT 2: since only a few pieces weren't cooperating, I animated their "roll" values about every 10 or 20 frames to maintain a more or less correct position. All in all everything is working out like I wanted, Woooo!!! time to go celebrate at the gym!

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05 May 2008, 06:17 PM
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