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Skeleton root bone scale incorrectly set to 1 in animations after "Imported bone transform is different" error, resulting in smaller/bigger meshes in animation

The root bone scale in a skeleton is incorrectly set to 1 in animations after you import a skeletal mesh getting a "Imported bone transform is different from original. Please check Output Log to see detail of error". The error itself is caused by the Blender exporter scaling all of the bones in a rig instead of only the root bone.

Because the root bone scale is set to 1 incorrectly the animations look wrong. If the mesh was scaled 100 times the root bone scale should be 100 in animations too, but in the case of the error it's set to 1 so the character is 100 times too small in the animations while looking fine in Persona skeleton/mesh mode.

FBX files here:

To see normal scaling behavior:

  1. Import blender001scale.fbx with Import Uniform Scale set to 10 and importing animations.

  2. The skeleton root bone has 10 scale in the skeleton view.

  3. The skeleton root bone has 10 scale in the animation view.

blender001scale.fbx was exported using metric 0.01 unit scale in Blender, which works but causes issues in other parts of Blender.

To see faulty scaling behavior:

  1. Import blender1scale.fbx with Import Uniform Scale set to 1 and importing animations.

  2. You get an error saying "Imported bone transform is different from original. Please check Output Log to see detail of error" because on export from Blender all bones were scaled instead of just the root bone.

  3. The skeleton root bone has 100 scale in the skeleton view.

  4. The skeleton root bone has 1 scale in the animation view. This is a bug, it should be set to 100 like in the skeleton view. Because of this the animation is tiny.

blender1scale.fbx was exported using metric 1 unit scale in Blender, which at the moment causes issues with UE4 but works perfectly with other areas of Blender.

Product Version: UE 4.16
blender fbxs.zip (2.7 MB)
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asked Jun 07 '17 at 02:03 PM in Bug Reports

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avatar image Glitchdove Jun 07 '17 at 06:18 PM

Sorry if I'm posting this comment in the wrong place or something, only creeped before and never posted! (Thanks for making this post btw)

I wanted to say that I have this issue with the newest version of unreal - spent all day yesterday fidgeting with the settings in both blender and UE, no luck. I moved back down to 4.15 this morning, reset all of my export/import settings to how I usually do it, and it imported just fine.

It's really frustrating - look forward to seeing this corrected.

avatar image aWinter Jun 30 '17 at 03:10 PM

Think this may be related to the crude implementation of the armature bone removal. We had to modify the blender exporter so the fbx don't get recognized as blender file, keeping the armature bone untouched. We don't have any Issues this way.

There are many people who DON'T want or need the Armature Bone REMOVE d So please Epic... If you touch the Blender fbx Importer again, make sure that you expose a bool to the import options or console command to keep the armature untouched. Thank you.

avatar image huwp Jan 08 '18 at 07:43 AM

A workaround that I found: Rename "Armature" to something else.

I personally call it "Root" and have it mimic the root bone.

avatar image cyaoeu Jan 08 '18 at 12:13 PM

That's not a great workaround because it means you can't animate root motion in pose mode. I would rather use the 0.01 scene scale workaround until this bug is fixed.

avatar image m.duman Jul 11 '19 at 03:19 PM

Bump. This bug is back with Unreal 4.22.1 and Blender 2.8.

My mesh has its rotation and scale applied. All scales are 1, all rotations are 0. Mesh & Armature look fine in Unreal's Skeletal Mesh view and Skeleton view but the animations are too tiny (root bone scale is 100, rest are 1).

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