Blender to UE4 Skeletal Mesh Explodes with Seemingly Multiple Roots

Hiya Unreal Community,

I’ve been struggling with the Blender (2.74) to Unreal (4.8 - 4.9) pipeline for quite some time now. Currently, I’m trying to get the physics asset working from an imported Blender file. Unfortunately, despite a seemingly sound bone hierarchy, Unreal appears to treat everything on the second level of the hierarchy as its own root.

With all constraints locked, shouldn’t the mesh not deform at all?

Here’s what we’re dealing with. A couple of adorable space things.


Here’s the order of events.

  1. We’ve got our mesh, with the skeleton showing. Something definitely seems amiss with the root bone section.
  2. Simulating, with gravity. The head appears to be detaching from the body as gravity takes its toll.
  3. Dear lord what have we done.
  4. Exploding mesh. Which is cool and all, but not quite what I’m looking for.




Again, all constraints are set to locked, and the same occurs when all collisions between bodies are disabled. Any thoughts?


EDIT 9/8/15: Some new insights:

  • When Linear Constraints are set
    to free, everything seems to be
    relatively normal, apart from the
    hierarchy showing the root bone as
    flying all over the place due to the
    rotation of other bones.
  • When Linear Constraints are set
    to locked and Linear Breakable is set to true, with the exception of some bones that erratically fly off, it behaves similarly to when Linear Constraints are set to free. There is little constraining to be seen.
  • When Enable Projection is turned on, the entire mesh flies around erratically, usually going off-screen within a second or two.
    Does this help identify the problem at all?

Also, here are the settings for the .fbx export from Blender, as well as the bone hierarchy in Blender.

I have been struggling with the same problem for quite some time now and can’t get it to work and I don’t know why :confused: I hope this resolves quickly :slight_smile:

Here’s a related incident: Working on an entirely different mesh, trying to make a tail be simulated. I created some basic body capsules for the tail, and set the main tail part to “Simulated”.


For whatever reason, this works fine when the root is simulated; it just falls into a heap on the ground as expected.


However, if the root is set to be kinematic, the tail immediately shoots apart from itself into the air, and then falls down retaining its long shape.


None of the bodies are set to collide with each other. Any thoughts as to why this is happening?

Yeah, unfortunately this is still an ongoing issue for me since 2014 (A blender user who refuses to make the switch to Maya yet). A fix that I found was having a dummy collision body on the Armature bone (I.E. Disable Collision Detection and Disable Collision in the Constraints tab) This solves my issue, although some issues still occur when the bones are in a strange hierarchy

Hope this helps! (Years later)