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rustymclellan
10-13-2005, 03:28 AM
Hello everyone,

I'm a first time poster here and love everything you guys do. It's amazing to see such a thriving area of artists all in one place!

I have a few questions I was hoping to have help with. I've been working on rigging for the last couple of weeks and have a few questions.

First: I've made legs and a spine and am now working on IK solvers for the arms. I've made 5 joints for the arm (collarbone, shoulder, elbow, forearm, and hand). My question is this: when I make one IK handle for the left side, the pole vector does'nt start in the same place as when I make an IK handle for the right arm, thus the arms do not move the same. I know about joint orientation to some extent (axis down the bone), and I think this may have somethign to do with it, but my pole vectors do not come out to be the same on either side unless I use the twist attribute on one side, any ideas how to achieve this symmetry?

Secondly: I was wondering if someone could give me some help on the "contrains" maya uses. I've been using point, parent, pole vector, and orient among others for rigging. Can anyone give me a break down of why certain constraints are used for different situations (examples?).

Hopefully I haven't rambled on too long. I'd be grateful of the help =)

Dichotomy
10-13-2005, 04:26 PM
ok, some things you might check... have you set preferred angles for the elbowJoints? that can change the way that the ik interperets the bend of the joint. It almost sounds like this might be the issue... since you can use the twist to adjust the direction of the bend. To set the preferred angle, orient the joints correctly, then bend the elbow in the direction that you want it to bend (should be on one axis), then in the skeleton menu there is the set preferred angle option.
or is it the joint that bends? That has to do with how you set up the Ik. for an arm you only want the ik to be on three joints. You can then move the effector's position to the wrist and connect that to the control.
Constraints...
PointsConstraint: is a tranformation to transformation constraint. use it when you want one object to follow another object's transforms. the controllers of iks is a good example.
OrientConstraint: is a rotation to rotation constraint. this one I use in things like the head control, switching between fk/ik setups on the skinnedJoints, the control that makes the wrist bend, stuff like that.
ParentConstraint: works like parenting an object (for trans/orient) without the hierarchal setup.
PoleVector: used with ik's, controls the bend area of the joints, ie. moving a bent elbow or knee.
Aim: translation to orientation. use with eyes so that you move the control (translate) and the eyes follow (rotate).
Those are the basic ones. Let me know if setting preferred angle worked for you.

rustymclellan
10-13-2005, 11:53 PM
As always, great input on the problem at hand. The pole vector does indeed orient itself on the shoulder joint based upon the preferred angle of the elbow joint. I believe that you have to do this before you set the IK? Not entirely sure but this was definately my problem, so thank you. One last thing, if you have time to answer: the parent constraint could work just the same as point or orient, why would I choose to use this when I could use either orient or point? Thanks for your help again!

Arcon
10-14-2005, 12:50 AM
One last thing, the parent constraint could work just the same as point or orient, why would I choose to use this when I could use either orient or point?

a parent constraint works differently. the constrained/child object on a parent constraint will change its position relative to the orientation of the master object, ie, as if it was parented. whereas if you point and orient constrain an object to another object, when the master is rotated the child's orientation will match but its position won't change.

i've found parent constraints useful in character rigging where you want certain deformers to act as if they were parented to a joint, but not include them directly in the heirarchy.

Dichotomy
10-14-2005, 12:56 AM
exactly what he said above about parent constraint... that is what I was trying to get across, but he said it a lot better :beer:

as far as the set preferred angle, it does have to be applied before the Ik... there have been tons of times where I forget, get the arm set up, then have to delete the ik, set the angle, and set up again... ... but at least the rig works then :thumbsup:

Andrei2k
10-14-2005, 06:00 PM
Parent constraints rule! I've always used them for various uses and the bonus of acting like parenting happen without including 'child' in hierarchy is that you can set up layers to hide specific area or just plainly being able to organize your hypergraph and entire structure in a more intuitive manner.

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