Applying Spline IK Constraint

How do I apply a spline IK constraint to an armature? There doen’t seem to be an apply button. I am assuming it is possible to apply the constraint…

Say I want to make an animation of a rope unfolding. The rope is attached to an armature. There are two curves: curve 1 represents the rope folded up, and curve 2 represents the rope unfolded.

First I add a spline ik constraint to the armature so it follows curve 1. I then apply the constraint, and then add a keyframe for all the bones’ rotation. Then at frame 50, I add another splinke ik constraint, this time making the armature follow curve 2. I apply the constraint, and add another keyframe of the bones’ rotation. This would result in a smooth animation of the rope unfolding.

Is there a reason that you are not just putting a key on the IK bone at frame 1 and then advancing to frame 50 and adding another key?

If you really want to save those positions for some reason, then you probably want to get the rope positioned as you want it then save that pose in your Pose Library. Your ‘Armature’ object lets you remember specific poses that you can recall later. This is the closest that you will get to being able to “apply” the IK solution to your armature.

If I add a keyframe of the bones’ rotation with the spline ik active, then I remove the spline ik constraint, the bones go back to their original positions. Adding a keyframe when there is a spline ik constraint, is the equivilant of adding the keyframe when there is no spline ik.

What happens if you have both constraints present and animate their influence values to crossfade? Alternatively, you can add a second armature and try to match the behavior. I’m not sure if adding keyframes to the pose library would work, but you can try that also.

Weird. The usual approach for animating spline iks that I have seen are to add hooks to the spline and then animate the spline using the hooks. Is that a workable solution?

Having both ik constraints present and animating their influence doesn’t work. The second constraint is completely ignored if the first constraint influence is greater than zero (i.e. even if it is 0.0001).

I didn’t try adding hooks to the curve, but I did try using shape keys. I had 2 shape keys defined for the curve, one for the initial position of the rope and one for the final position. However, this gave a weird looking animation - the rope when from the initial to final position in a way that was very unnatural for a rope.

In the end I gave up and manually positioned the bones along the curve, and keyframed their rotation. This gave the animation I was looking for, but was a tedious method.