IK handle for 1 instead of 2

[bwrtz]

Hey folks,

Here's a quick issue which hopefully I can describe simply ....

So from what I understand, part of the beauty of IK handles is so you can *move* the wrist/hand (instead of rotating the elbow or shoulder), and everything behind it rotates and moves properly. The normal way I've seen these things work is it's usually set to a value of 2, which from what I understand means it affects everything back to the shoulder. But what about getting this behavior across only 1 joint? I hope no one tells me I'm crazy for wishing for this, I've seen it in other programs. The best example is right here in the sample "alien walk" demo file in the cheetah samples folder (it actually does not work in that file, nor does it work in any of my attempts). If you click on the elbow and *move* it (not rotate) it just kind of awkwardly stretches it. I was expecting that if you set an IK handle here with a value of 1, you would be able to move the elbow and the shoulder would automatically pivot to accommodate. That seems to be the way it always looks in character rig tutorials in other programs. Also the fact that the IK handle in cheetah has a convenient value set thing, usually set to "2", it makes me assume that setting it to 1 would get it to do this. But when I set it to 1, it actually prevents the elbow from moving at all. So I guess the question is how do you set it so moving the elbow automatically pivots the shoulder, or another way of putting the question would be what is an effective and proper use of the IK handle with a 1 value. Hopefully this makes sense, and I'm sorry if it's already been covered somewhere.
Thanks!

 

[ZooHead]

So are you trying to shrug a shoulder?

Try adding a point constraint to the bicep bone and set it
to Target a sphere, cube or spline as a control object.

Have it constrain only the Y axis. To shrug simply move the control object up or down.

 

[bwrtz]

Not trying to shrug, but that is an interesting technique. The only problem is it won't work if the character is ever sideways. Tried putting the targetted object in a folder with the alien (I'm simply using the alien from the Alien Walk example, to be sure I'm using a good example), and that lets the rotation take the sphere with it, but, the 'shrug' gets offset when the transformation occurs ... BUT ... not trying to shrug, a better example of what I would be going for would be to be able to move the elbow (not rotate, just move) the elbow and have it automatically rotate the shoulder and bring the bicep with it properly. You may say this could easily be done by rotating the shoulder instead, but that gives less control over where the elbow is located, and also the other reason this is puzzling me is because I actually thought this is what IK value 1 was supposed to do, ... so this is partially just trying to understand IK handles better, because I know I need to have a rock solid understanding of those things because a lot of the kind of work I'm doing depends on them. Actually, to be more specific about something I would actually like to do, it would be to keep the hand and the shoulder both still and be able to move the elbow. (with the bones to follow! doesn't count if it just stretches the skin). The targetted sphere technique actually seems mostly solid, but this breaks down if the character is not completely upright all the time. Hopefully all this makes sense. Any other ideas? thanks again!

 

[ZooHead]

I think adding a Pole in the IK Handle Tag will do that.
It controls where the knees or elbows point.

 

[bwrtz]

This is so close .... it does what you said, but, only after you kind of nudge the foot. While you are just moving the target ball around, you don't actually see the knees go anywhere. you have to move the foot. Any way way to do this so the knee moves while you move the ball and not having to touch the foot? hopefully that all makes sense.

 

[bobziila]

On this leg/foot rig, just move the pole vector and see if that's what you need.