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FBX export of armature using Spline IK looks very wrong
Open, Needs Triage by DeveloperPublic


Blender Version
Broken: 2.79

Short description of error
I'm working on a lasso rig using Spline IK. Things seemed to be going okay until I did a test .fbx export. It seems Blender's having trouble correctly baking the animation due to the Spline IK constraint.

Here's a screen grab of what should be the same action being played back together. On the left is what it should be, on the right is the .fbx export.
As you can see, the export goes crazy.

Attaching the .blend file:

To reproduce the error

  1. Export an .fbx of the original animation.


  1. Bake the action.

Either will show a craziness unlike the original animation.



Event Timeline

Seems like a scale/stretch related issue? If so, it's not a bug, Fbx does not support it: the scale value of each bone inherit the scale of the parent bone.

Hi, @lucas veber (lucky3), thanks for the response.

I'm not sure it's solely an Fbx issue. If you just bake out the original animation within Blender, you'll find the bake is all wrong, too. I have a suspicion the sporadic nature of the Fbx export has ties with the fact that Blender itself is having trouble with the rig's logic.

The main problem in this scene is the cyclic dependency, that is likely introducing issues when it comes to animation baking.
It's a common problem with Spline IK constraints. You can open the Blender console to see the error log, and when moving the rig bones, there's also a one frame lag which is due to the cyclic dependency issue.
The dependency graph is being re-written for Blender 2.8 to avoid this (as far as I know), for now only this kind of rig setup should be used with IK Spline constraints:

The FBX format supports both scale - translate child or scale of parent also scales the child, it is a setting, Maya and MotionBuilder can change this and FBX supports it.