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  • IK vs Pose [Improvement for the IK]

Hi team

I really love the way that the Pose makes the rotation of the bones selected like a Tail where we can control the direction of the bones and the rotation.
but we know that animate each bone when you have a complex project is not very easy and optimized to handle key by key.

I've uploaded here an image with the comparison of the Pros and Cons of IK and Pose.

Why IK can't do like Pose do when we move the selected bones?

Is possible to have IK with multiple bones to animate a kind of Reptile Tail at the end, and moving this IK the Bone follows,
as we do use the Pose with multiples bones selected

I tried to use Path, but to set Path with IK and bones it's very difficult to handle.

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Hello,

first of all, why are you using IK on a tail? does the tail need to be pinned to another object, as if the animal is trapped to it by the tail?
If the answer is no, I'd recommend not to use IKs at all, as by nature tails work best when they follow the main motion.

To answer why IKs cannot move the way you envision, is because each IK can only have one possible solution to be able to be reproduced at runtime.
More about IKs limitations here: Inverse Kinematics - Spine User Guide: Limitations

The good news is that you can set the IK mix to 0 at any time to be able to move it freely when needed during the animation.
Inverse Kinematics - Spine User Guide: Mixing FK/IK

The pose tool is great! I use it a lot, but specifically for tails, I find that animating them using the offset tool gets the most natural results:
Dopesheet - Spine User Guide: Key Offset

Image removed due to the lack of support for HTTPS. | Show Anyway


Spine Tips: 27 offset

What Erika posted is spot on. I'll just add that 1- and 2-bone IK constraints are deterministic: there is only one solution. When there are more than 2 bones, there are many solutions, meaning there are many bone rotations that result in the tip of the last bone being at the IK target. That means the pose resulting for more than 2 bones is dependent upon the pose in the previous frames.

That creates a number of problems. For example, if we want to pose a skeleton in the middle of an animation, there is no previous pose. We could do something like start from the setup pose, but the result is unlikely to be the same as if we had played the animation from the beginning. Playing it from the beginning and posing it on multiple frames so we have the right pose in the middle of the animation would be a lot of computations.

Lastly, as Erika mentioned, getting exactly the behavior you want from IK with more than 2 bones is difficult and you are usually better off animating it in other ways.