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25-11-2002, 05:23 AM   #1
dkouts
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Getting IK to work in reverse...
Consider a simple leg joint chain :

*Hip

*Knee

+Ankle

OK, you can grab the ankle IK handle and drag the leg into a pose,
but suppose you wanted to grab the characters hips and push him
down (as if preparing to jump) how do you make the ankles hold
their position, on the 'floor' and have the knees bend logically as
when moving the ankle IK handle up?

Effectively animating with IK, but from the top down?
Whenever Ive laid down a quick IK chain in Houdini, I was always
able to just grab the 'top' of the IK chain and have it work as I described.

But maybe theres an extra step in Maya that Im missing?

Dan
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25-11-2002, 06:03 AM   #2
mtmckinley
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It works for me, but it might be because of the way I create a foot structure for animation purposes. I've attached an image of what I do in this thread:

http://forum.simplymaya.com/showthre...?threadid=2034
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25-11-2002, 07:11 AM   #3
dkouts
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Thanks for the reply, Mike. nice image!

So taking my simple rig as an example -

hip,
knee,
ankle,
connect with IK handle...

would you EXPECT the hips to be able to drive the knee rotation
with no more parenting / IK tooling than that?

Are you able to replicate that effect just quickly in a side view, for example?

Dan
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25-11-2002, 03:49 PM   #4
Kurt
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dkouts, Mike builds a great skelly!!! his setup is pretty much the same as I do.

Skeletons can be a pain in the butt, the nodes are set up and parented diffrent ways depending on what your little guy will be performing.

Most of the time just selecting the root joint, is all you need to get the character to bend at the knee's (like getting ready for a jump) while the foot stays planted.

What node are you selecting in the hypergraph? Did you put your IK nodes into the same chain as the rest of the skelly?

If you did that might be the problem right there, most of the time if the character is just going to be runing and walking about, the ik nodes can stay out, If you want to jump and tumble you have to make a new node buy grouping the Root joint to itself, then parenting the IK's to the new node you made.

It sounds like the node your picking in your chain might have been grouped with the root and ik's together which will select the whole skeleton together making a node that highlites all the joints and moves all the joints at once.

If you do have the iks parented to your root joint try unparenting them. Once you have done that select your root joint again and group it to itself, call it (Flip) or something along that line and add the iks to that node. Now if that was what the problem was select the root joint only, you should be able to get the up/down action your looking for while the feet stay planted. Then if you select the new node you made called flip that should select the whole skelly and you should be able to flip him if you wanted him to jump head over heels.

Its a bit hard to say what the problem is with out seeing the way you set-up the skelly=)

Hope that helps, they can be tricky


Kurt
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Last edited by Kurt; 25-11-2002 at 04:04 PM.
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26-11-2002, 12:04 AM   #5
dkouts
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Thats got it!
Kurt, you are my new best friend!
I was grabbing the root joint in the outliner, but there was no group node parenting it. I have gotten it to work thanks to your description.

And Mike, thanks for your reply too.

I will be telling every Maya user who asks me about web resources to check out Simply Maya - I get more results from the guys in this community than the Alias Wavefront Official E-Support website.

Hope I can contribute more when I get more experienced.

And Mike, Ive checked out your tutorial site too - very helpful as well.

Dan:banana:
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26-11-2002, 12:12 AM   #6
Kurt
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Glad I can help bud=)
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26-11-2002, 12:21 AM   #7
mtmckinley
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glad to help.
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30-11-2002, 06:28 PM   #8
DukerX
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"Sticky" IK handle
You could also make the IK handle "sticky" in the properties editor.
That would make the IK handle stay in place when you move the hip around, and animate the legs according to the movement if the hip.
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02-12-2002, 02:51 PM   #9
dkouts
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Thanks Duker. Is 'sticky' a Maya tool, or are you using that word just to imply locking the feet down?

: - )

Dan
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02-12-2002, 04:38 PM   #10
kbrown
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If you key the feet translations and then move the root joint, the feet will stay locked down.
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