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View Full Version : Rigging - hips and shoulders



leinart
03-09-2003, 08:13 PM
I'm rigging a character, and have run into a problem. I've gotten everything set up for a wide range of motion, including the key features most "rigging priority lists" say, but I have one step left that I can't get to work.

I'm trying to set up the hips and shoulders with IK to move seperately. I'd like to be able to swing the hips from side to side (not just from the waist) while holding the shoulders locked in place. (and also be able to move the shoulders around from the top). So I put a null in around the shoulders, and set it as the goal for the top spine bone. And it works great for the purpose, but it messes up other parts of my rig. As I move either this null or the control for the hips, my arm moves just as much in strange ways (forearm only), even though the IK goal for the arm remains in place.

Anyone else out there had this problem? Thanks,

John

SplineGod
03-10-2003, 03:52 PM
why do you have unaffected by IK and IK applied to the same bone? If you need to move the hips separately from the shoulders simply set up separate bone chains for the upper and lower body.
I dont and wouldnt rig the shoulders and hips the way youre describing unless I have a very specific reason to.

leinart
03-10-2003, 06:22 PM
Thanks for the reply. I'm not really sure how to do this - which is why I'm asking. I just know what I want the character to do.

I'd like to be able to grab a control at the hips and move it back and forth/side to side while the feet and shoulders remain in place. No prob with the feet, but the current setup I have uses FK only for the spine bones.

Seems like making an IK chain for the back is the best answer to the problem, but I've tried this several times in the past (and now), and never gotten it to work.

The feet and hips work perfectly, and so do the arms and head/neck (all IK chains) but this doesn't. What I did is add a null at the base of the neck and set it as the goal of the top spine bone (while setting the other spine bones on IK). The system works, but moving the hip or new shoulder control makes the arm bones whip around (independant of their own IK goals).

If this is the wrong way to go about it, I'd gladly re-rig the whole character - I just don't know another way.

Thanks,

John

SplineGod
03-10-2003, 06:44 PM
Lets start with the first part. What does the character need to do and how did you decide that?
The Hips also need to rotate from side to side as well. That way the hips rotate depending on which leg has weight over it etc.
If you use IK to control the spine, how do you get the spine to rotate, twist or bend? Try this: select all the spine bones and hit the y key (rotate). Now you can bend and twist the spine bones additively. If you create a selection set in the scene editor you can easily reselect the same spine bones everytime. This also works well for fingers.
The idea behind a good rig is to make it as poseable as possible.
You dont want it to behave like a real person. When you pose it, moving some some other part of the rig shouldnt make other parts change their pose otherwise youll be fighting with the rig.

leinart
03-10-2003, 07:08 PM
The multi-select option is very nice! Didn't know you could do that. I've used expressions before to do the same thing. Is there any way of accessing that selection set from somewhere else, say, a slider?

I agree, this does make a good way of bending the back, and like I said, I've used it before. However, what if I want to swing the opposite way? What if the character needs to swing his hips without his shoulders moving? If you want an example of the motion I'm trying to get, go look at the walk cycle in Alien Song. The swinging hips there couldn't have been done with FK because of how rock-solid the shoulders stay. Somehow I need a combination of the two methods we're talking about here.

I know this has to be possible, but I can't get it to work. Even if I don't have to have it on this character (which I'm not sure of at this point), I know it could have been a help in the past, and most likely in the future as well, so I'd just like to figure it out.

I definately agree with your comment on keeping the rig poseable - that's why I'm bringing this up :)