Thursday, July 21, 2011

Leg & Foot Rigging: Trial and Error

After trying Tob's tutorial for the first time yesterday, I failed. Not completely, but things weren't working right. I was trying to apply it to my model while watching the video. I renamed bones differently because I didn't like his conventions and so forth - that may have thrown me off.  Last night I spent a few hours toying around with what I've learned so far until I got tired.  It seemed pretty hopeless in the moment, but I learned some IK behaviors in the process.

Today, I started Tob's tutorial afresh from the basic scene - no mesh - no nuthin.  Maybe things have settled in my brain a bit better - I've succeeded in getting through videos 2 & 3 which are the hardest parts (so he says. I'm feeling better about this whole IK thing, but really, I just can't wait to get to the point where I can start animating some actions properly.

Here are some questions that I had, my solution, and links to the source.

Q. Why are my bones with IK constraints showing as orange rather than yellow?
A. The bone is not being targeted "correctly". In order for a true IK to work you must target a bone that is outside the chain / is not parented to any bone in the chain with the IK. If the bone is targetless or if auto IK is on, this  means that when you are animating you have to track all of the bones in the timeline individually vs. only having to track the targeted bone.

revolt_randy on :

First off, you don't have a proper IK setup. Notice how the bone with the IK constraint is orange in color. That means there is an error, proper IK constraint setups are yellow in color. The way you have it set up, it works as a 'fake Auto-IK'. You can use it this way, but you have to do a couple of things. First, when you set your keyframe on frame one, you will have to set rotation keyframes for all the bones. It's easiest to just select all the bones, and set loc/rot keyframes for them all. Then make sure you turn on auto keyframes in the time line. (that's where I had my stupid moment) Now advance to frame 31, grab you bone with the constraint and move it. Keyframes will be made for the bone you moved and all other bones that were moved. Then it works how you expect it to.

You can also, remove the constraint, and in the toolshelf, select the 'AutoIK' option, then repeat as above, does the same thing.

To make a 'proper' IK chain, you need to add one more bone, which acts as a controller for the chain. This extra bone cannot be parented to any bone in the IK chain. Then you can control all the bones in the chain by just keying this one bone.
view entire thread

Q. How do I lock rotations in an IK chain?

Inverse Kinematics options

A. The closest thing I've got is the documentation on,  but the documentation is for version 2.4:
I've found that in 2.5 the options / settings are in (Armature Pose Mode) Properties Window > Bone Panel > Inverse Kinematics.  Here you can lock the bone from rotating in certain ways even if it's in an IK chain.

In order to limit a bone's rotation / location / scale in any other scenario, you can select the bone, then add a Limit Rotation / Location / Scale Bone Constraint from the Bone Constraints Panel while in Pose Mode, or toggle Transform Locks in the Bone Panel while in Pose Mode.

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