View Full Version : elbow twist (pole vector)

02 February 2006, 01:26 PM

I'm setting up an IK/FK arm. And there is one thing on the IK control I would like to make, so it work as I want to. When I make the pole vector constrain on a control objekt that works ok. But I tried the Leon rig (if anyone knows it) and it had a elbow twist attribute. So you could rotate the wrist and move the arm around without thinking about the pole vector. And then rotate the elbow with the attribute.

Does anyone know how to make a setup like that??? Would make my day...

02 February 2006, 02:54 AM
Hmm...Haven't seen the Leon DVD. But it seems like the "twist" attribute on your IK handle.

Select the arm IK, you have a twist attribute for it.

If you want to control this from your IK arm controller. You can just add and attribute and use the connection editor to connect the attributes. :D

02 February 2006, 10:43 AM
OK, I know how th RP solver works, but I still have to animate the pole vector around to avoid flipping. But they do actually use the twist attribute to control it, but I never could figure out the rest of the setup.

02 February 2006, 03:35 PM
Well. In a sense, you can animate the twist attribute to avoid flipping. It works almost the same as the pole vector.

I've rigged some characters with the Twist attribute as the control for the knee and elbow rotation a few times for animators who've preferred it. (It's all up to preference. If you want to animate a pole vector contraint or an attribute.)

02 February 2006, 11:06 PM
U need to use a pluMinusAverage node, or at least that's the way it's done on Leon. Check out the cgToolkit website, and get their first book, it goes through all of that stuff. :)

02 February 2006, 01:29 AM
here's a link ( Check it out for your pole vector problem....ok I know its a bit of a cheat, but this is gonna get ou the same kinda results...

02 February 2006, 05:15 AM
hi ArePAre,

if i remember right :

the concept of avoiding the flipping of the IK is cleverly addressed by LEON's method.. by having the RP solver 's plane pointing 90 degrees off the current (rot.plane - at creation time), which wud avoid the flipping b'se u've offset the RP 90 degs away and u keep that offset always and thats how its avoided ... if wrong, pls correct me guys !

now to do it,.. select ur IK HANLDE and ur anim_ctrl and go to hypergraph.. and there.. u create a +-avg node. to ur anim_ctrl, you add two attributes - offset and Twist (floats) and then u pipe these two attributes to ur +-avg node 's input1X and input2X and then set the +-avg node to sum.

select IK_Handle and negate the pole_vector X,Y,Z to zero, n this is where u have to choose, which axis u need to choose to put a value say -1 or -.01 ,, this value now makes the RP solver to point in this particular axis.. say u give -1 in pole_vector_X the the IK will aim in -X axis n say u gave 1 in pole_vector_X the ik will aim in +X axis meaning theres a 90 degrees offset from the creation-time's rp plane - select ik handle and observe the upper cirlce with the pointer...confusing ? sory.. but ...

now connect the outputX of the +-Avg node to ik-handle's twist attribute. so u can adjust the offset attribute on the anim_ctrl to -90 or 90 to match back to the original aim direction.....

ok, now select the offset attribute in channel box and lock n hide it.. now use the twist attribute on the anim_ctrl to aim ur bone-chain ............super cool trick by the cgtoolkit gurus !


03 March 2006, 10:45 AM
Thank you alot guys. I tried the plus minus setup and liked it alot.

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