Aim constraints & IK... or something like that

# 1 12-06-2005 , 08:42 PM

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Aim constraints & IK... or something like that

I want to set up something similar to an aim constraint, but this isn't a "aim the eyes at the target" kind of thing.

I'm working on a UT2K4 model and want the arm holding the weapon to establish something similar to an aim constraint so that, as the model wiggles around due to it's running cycle, the arm maintains some sort of aiming vector where it's constantly pointing at something in the distance.

The arm has simple IK connecting the forearm twist joint and the shoulder. The wrist and fingers are raw joints. I've successfully used point constraints to anchor the pole vector locator to a point in the distance, keeping the elbow from wiggling around, but I want to do the same sort of thing with the other end so the gun hand doesn't wiggle, either.

All the help (Maya & otherwise) I've found so far deals with aiming standolone objects (like eyes) at something, but nothing quite like this.

Any suggestions?

Thanks.

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# 2 12-06-2005 , 09:23 PM

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All you would need is an orient constraint on the wrist joint to force the hand to maintain a certain rotation. You could constrain the wrist joint to the IK handle or use another control object entirely, depending on how you have your rig set up.

Danny Ngan
Animator | Amaze Entertainment
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# 3 13-06-2005 , 11:23 AM

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I tried something similar to that, but received an error message. What I tried was using an aim constraint on the wrist joint, and using a locator as the target. I didn't quite understand what the issue was, but I assumed that it had something to do with all the fingers being selected as well due to the parenting when I selected the wrist, and I must have had too many contrained things.

I'll try the orient constraint tonight. Is there something I need to do to select only the wrist without Maya automatically selecting the rest of the chain, or can I just select the wrist as the constrained object and Maya will be OK with the rest of the chain being selected as well?

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# 4 13-06-2005 , 09:05 PM

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Y'know, I was thinking about this and realized that what I really want is to have the constraint on both the elbow and the wrist. The wrist doesn't really move around a lot in these situations - the adjustments are through the whole arm. To do that I think I'd need to remove the IK on the arm and just use the joints.

That's fine for my situation because it's just for 20 frames in a very specialized and simple scenario. I can isolate it to a single file and it won't affect any of the other sequences. But how would a person do something like this with a complicated rig in a long, complicated scene?

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# 5 15-06-2005 , 09:16 PM

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The error I was experiencing was due to limiting movement along axes for the elbow and wrist joint (so that they couldn't go in directions the real items can't). Once I freed up each joint to rotate in all axes, I was able to set the orient constraint on the joints. However, the IK prevented it from having any effect.

How do people with IK do this sort of thing?

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Aim constraints & IK... or something like that

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