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redbox
01-16-2004, 10:16 PM
ok, this is an OLD problem that has plagued my animation for ages, and ive looked and looked and never seen it addressed, so i guess im the only genious who cant figure it out. so, after years of wasting time fighting it and stressing, i finally figured perhaps i should just ask for the directions (yes, im a guy). heres the prob:

i wish to animate arms of bipeds with IK. at one time i may wish to have a char lift a gun from his side and aim it (elbow out version), at another time i may want him to lift a dumb bell and curl it (elbow down version). the ik null movement isnt identicle, but close enough, the only diff is that i rotate the arm out for one and down for another. no prob. IK it, then go back and clean up the elbows with a z axis rotate on the "excluded from IK" shoulder bone. Now when i do this the arm doesnt want to rotate like that and so it does a popping bit between not responding and then way over rotating.

The way i figure it this is due to the fact that I am trying to rotate the entire ik arm unit on the z axit of the shoulder while leaving the null stationary instead of rotating on an axis defined as running between the shoulder bone and the null. OK, set the shoulder bone to point at the null automatically. great, but it only will auto rotate that bone on keyframes, not tweened frames, so im ending up having to animate the nulls normal, then go back and bake in the animation so its all keyframes and the shoulder will point correctly and ill have my nice axis. so now that im baked animation i gotta tweek the arm rotation on every keyframe FK and then go back, and fourth cleaning it all up. MAJOR time waster and I cant imagine that ANYONE actually wastes this time but me. any help on how to rig the arms and shoulders so that i can IK and still pick the arms z rotation (direction elbow points) would be of great help. thanks guys. lemme know if you need pics, sometimes i describe poorly.
-chris

Dodgy
01-17-2004, 06:20 AM
I have 3 bones, one from the spine to the shoulder(called shoulder), one from the shoulder to the elbow (called arm) and one from the elbow to the hand(called wrist) I have them flat in the y axis, with a slight bend at the elbow to teach the IK which way to bend. I have IK only on the P of the wrist, and only on the HP channels of the arm. I then key the B of the arm to position the elbow. Other people have much more complex rigs, but that's how I have mine and I've done loads of anims.
There's a free plugin out there called IK blender, look for it on flay too. It allows you to to go from ik to fk using a channel.

redbox
01-17-2004, 09:52 PM
thanks for the suggestions. I think perhaps i didnt do a very good job of explaining the problem. but, out of curiousity, your arms dont ever have trouble being positioned how you want them when you rotate by the bicep in z? I posted some pics I think will clear stuff up a bit, although I posted it in a posting called "arms a poppin" in the TIPS and TRICKS forum. Think thats more fitting a place for it prob. anyway, anyone who wants to see this thread further can do a search there. sorry for the confusion.

redbox
01-18-2004, 12:12 AM
btw, ik blender is no longer a valid link on flay.com. lemme know if you know of a diff place to find it. Thanks