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View Full Version : Knee, Elbow, and/or Shoulder Deformations...

Axercise
08-30-2004, 08:06 PM
Okay, i KNOW this is a very basic question here, but i just can't figure it out. And goin' through the Maya "help", i can't find any relative info for such a simple thing.

The back of the knees on my soft-skinned model deform... okaaaaaaay on their own, but i'd like 'em to deform WELL. How would i GUESS to go about this? Well, if i just select all the cv's at the back of the knee, and translate 'em a bit further back in Z when the knee is bent, it looks great. So i figure if i can get the rotation of the shin joint to drive the translation of these cv's, i'd be set. So i tried grouping those cv's in a cluster... but i can't translate the cluster along with my model as it moves... unless i turn "relative" on, in which case cool, but when i DO translate it in the bent position, the results are all whacky. I tried creating a lattice for these points and parenting and/or constraining it to the shin and/or shin and thigh bones... but by the time the knee is bent, the lattice has moved out of influence distance for the points, and moving the lattice is as useful as a bullet in the head. And i can skin the lattice to the bones, but again, it loses any influende on the cv's by the time the knee is bent. ...sigh...

Please tell me what i'm missing here. I don't think it's as complicated as i'm making it, is it? All i need to do is move a few cv's back when the knee bends! What do "those-that-know" do to tweak deformations on a knee, or elbow, or shoulder.? Obviously something that would travel WITH the skeleton, right? Or maybe not... i dunno anymore!

Please and thank-you,

AnimBoy
Wes
oshiroii
08-30-2004, 08:21 PM
WEll, I usually use an influence object or adjust the weighting. The weight stage can't be done in a short amount of time. Most of the time I'm tweaking it out for more than 2 days :cry: It can be a real pain in the ass.

But you said it was ok if you moved the vertices back, well you could adjust the weight so that the leg it's more like in the original state and the vertices look good. It'll probably cost a lot of time experimenting with weights. You should get this to look 99% good and give the extra 1% with deformers, influence objects, blendshapes etc.

Good luck :thumbsup:
john_homer
08-30-2004, 08:23 PM
....but when i DO translate it in the bent position, the results are all whacky....
thats because they are moving "relative" to the deformation generated by the skinCluster (joint rotating)
your best bet with this one is to use a blendShape,and have it "front of chain". Stahlberg has a tutorial on this, http://androidblues.com/ although I dont follow these techniques (totally) myself, I do recommend the bloendshapes on a single degree-of-freedom joint like an elbow or knee... you will get into trouble with a shoulder or hip due to gimbal if you try and drive them with simple joint rotation values, but thats another story... one that I dont have time to get into...

good luck
.j
MikeRhone
08-30-2004, 08:47 PM
In this case, if its only one row of points I would just use an influence object (A bone), driven by the shin, parented to the UpperLeg.

If you really want to sculpt with corrective blendshapes, Stahlbergs workflow works really well. John_Homer is correct though, only do corrective shapes on objects that rotate on one plane. Rotation orders and gimbal will really make this a migrain area. Influences objects will be more intuitive and controlable on a should or hip area.

As for why the points move strangely, again john_Homer is quite correct, the points are moving relative to the joint(s) that its weighted to. If you want to change this you can just re-order the inputs and swap the tweak with the skinCluster. (I forget which one should be first heh.)
Axercise
08-31-2004, 12:47 AM
Thanks for the suggestions and info guys.
I'll check out Staulberg's tutorial, and try one or two of the things you mentioned.

Cheers,
AnimBoy
Wes
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