I have been trying to animate my first human shape, and I followed some tutorials that made it clear I should understand inverse kinematics. Working with them is more natural, but trying to set them up is supernatural, as far as I can tell.
I ran into these two tutorials:
Blender Tutorial: Basics of Character Rigging by Sebastian Lague
and after my first problems, I looked into this to get a second impression of setting up inverse kinematics:
Blender 2.6 Tutorial 30 - IK Rigging Pt. 1 / 3 by BornCG
For an armature of a 3-joined lower body (upper leg, lower leg, foot), I added a IK bone near the foot, inverted on the Z so it could point out the heel. I then added a knee. Whatever I do, I kinda-sorta get something, but it never works quite like in the videos. It’s like I following along exactly, and when they do something, they got something perfect, and when I do it, my house burns down.
Right now, I can’t get the knee IK bone to do anything productive. I see that it is trying real hard to move some bones. It shakes and shudders when I try to control it from the knee, but it doesn’t move anywhere. The foot IK is doing a decent job. If I changed the foot IK’s chain length from 2 to 1, I can get the knee to work in a way I’d expect, but then the foot doesn’t really work quite right.
Another problem is I can’t figure out how to keep both the knee IK and foot IK locked to their positions relative to the areas they affect. For the foot IK, when I move it around, it can move free of the foot area which it controls. I was able to figure out to freeze rotation of the foot so I could rotate the foot from IK, but that’s it. I tried to move the knee away from the mesh in edit mode, which then just causes the knee to be bent forward when I switch to pose mode.
Also, I am still new to this business of rigging, so how do I constrain the knee so it bends in normal, human motions?
The rough process I have followed is something like this:
- New project
- Killed the cube
- Created an armature
- Created an upper leg bone
- Extruded from the upper leg bone to make the lower leg bone
- Extruded from the lower leg bone to make the foot
- Extruded a foot IK bone off the foot, and removed its parentage so it was free, free!!!
- Selected the lower leg and applied an IK constraint, targeting the foot IK
- Set the chain length of the lower leg IK constraint to 2. This had it go up through the upper leg
- Constrained the foot’s rotation to the foot IK, with Z inverted
- Extruded a knee IK bone from between the upper and lower legs, and removed its parentage so it was free, free!!!
- Moved the knee IK bone clear of the armature, forward of the leg.
- Applied an IK constraint upon the upper leg, targeting the knee IK bone, with chain length of 1.
- …
- Not profit
Here’s the file that has the aftermath of all that:
http://www.pasteall.org/blend/33895
Edit: I suppose I should add that I am not too surprised this doesn’t all work as they do in the videos. I’m having a hard time understanding how one can make an IK constraint fixed by a foot and get one effect, and then use the same process for a knee, which I would consider to kind of be a different effect and works upwards, and the other is at a junction and works upwards and downwards.