# Question Animation rigging for Inverse Kinematics

Discussion in 'Animation' started by Ominos_Amethyst, Oct 27, 2022.

1. ### Ominos_Amethyst

Joined:
Dec 15, 2021
Posts:
11
Hi everyone!

I'm seeking help about the animation rigging package and Inverse Kinematics. I've read a lot of Unity's own documentation about the package and seen a lot of tutorials on youtube, but I can grasp the idea to make what I want to work with the package.

I have a "leg" (image attached), and I want to move the tip and make every other bone move (IK) in just 1 axis (Constraint). However, I don't fully understand how to achieve it.
Keep in mind: there is 1 bone that is not visible, it is the tip bone at the far left of the picture.

I know we have the following constraints available for us:
However, I don't know very well how to utilize them to achieve what I've describe above.Nor do I grasp the concept of adding multiple constrains for 1 leg.

I did tried to use Two Bone IK Constraint, didn't work, given that my legs has many more bones.
I also tried to use Chain IK Constrain, it did work, but I was not able to find a way to constrain the rotation axis for each bone.

Any help in this matter will be extremely appreciated!

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2. ### CodeKiwi

Joined:
Oct 27, 2016
Posts:
119
I had a similar issue a while ago. I wasn’t able to solve it with the built in constraints and ended up making a basic custom constraint. I think I broke it up into two steps.

Step 1: distant to target.
• Two poses (min / max leg distance). Could be a masked animation clip or maybe min/max values for each x axis joint.
• The lerp value from min to max must always increase the distance e.g. each lerp value should be unique.
• Given a target IK distance find the lerp value that matches this distance. Could use a lookup table or just calculated at runtime. I’m sure there are better formulas but I just take the mid point a few times e.g. lerp 0.5 (less than target) => 0.75 (greater than target) => 0.625 etc.

Step 2: aim / look at the target.