Inverse Kinematics

ACK! I think they changed it… how do you do inverse kinematics?

add an armature with more than three bones. create any object. select the armature and enter pose mode. select the last bone in the chain, add an IK constraint. in the OB field, type in the name of the object you created. voila :slight_smile:

(can also be found in the 2.28 documentation - this hasn’t changed)

some ppl (actually most ppl here) tend to prefer the use o so called nullbones. theses are bones that actually don’t deform the mesh but are solely used as IK-constraint-objects. in this case, forget the “any object” you created. select the armature, go into edt mode and duplicate the last bone in the chain. make sure you unparent it from it’s predecessor.

then enter pose mode, select the same bone as in the first scenario, and in the OB field type in the name of the Armature. a second field appears, where you enter the name of the bone you wanna use as the IK constraint. i hope this is clear from now on :slight_smile:

marin

oh… . thanks… I only did it once… and that was maybe… last year…

Not since 2.20… :wink:

Martin

y’know… now that I think about it… I don’t think I’ve ever used inverse kinematics :o sorry for my moment of idiocy :stuck_out_tongue:

Just for the record…

“Inverse kinematics” is a $22.99 word for the simple notion that your forearm goes whereever your finger goes. You don’t consciously think about moving your forearm, probably; you point at things and the arm does whatever it must to get the finger to go where you want it to.

Brains sure do contain sophisticated programming… :slight_smile:

When you use IK, it’s like the same thing. The “finger” bone (or a null-bone attached to it) can be moved around, and all of the “arm” bones will automatically follow. Blender calculates the appropriate orientations for each of these so-called “parent” bones.

I’m curious, is there a way to control this orientation? or do we just hope to get lucky in bending the elbows the right way?

No - you set up another bone that rides a little bit off the elbow, behind it. Then constrain the elbow bone (you DID give your skeleton a little extra bone at the joint, didn’t you?) to that bone you just created with the LockTrack constraint. The elbow will then point to wherever you move that bone.

hm, no, not neseccary. the simpler way is to constrain the upper-arm-bone with a locked-track to a null-bone or an external control object. if you choose the right constraint-axes it works perfectly.

i like clean, simple rigs, that’s why i also never use null-bones but custom control objects - even if i can’T animate using strips… (waiting for that to come for every object).

marin

Or you can just fine tune the bending of the joint by rotating the bones (like a typical FK) which will affect how the IK solution is computed.

Martin

thanks much, I think I’ll try out harky man’s that’s probably what I’m looking for in my situations :smiley: