FBX export creates duplicate skinCluster nodes on some meshes

[bmagner888]

has anyone run across this issue when exporting skinned meshes as fbx files? It seems to assign duplicate skinCluster nodes to the same mesh. There is only one skinCluster on the mesh prior to export, but then multiple skinClusters on the resulting fbx file.

--detailed explanation--

I have an automated pipeline to export rigged character assets as fbx files for importing into game engines. It's a clean export containing only meshes and joints and blendshapes. It duplicates all the meshes and joints and rebuilds the asset in a non-destructive way so as to preserve the maya asset as is. All of this has worked as designed for over a year.

Today I am getting weird results. I have asset with many meshes, but two and (as far as i can tell, only two) meshes are getting multiple (4 in this case) skinCluster nodes assigned to them. I believe this is happening in the export because I can run the process in maya and see that they only have one skinCluster node in the asset file prior to export.

This is not a case where there are multiple skinClusters with different weights, joints, etc. There is only one skinCluster on the original mesh, and should only have one skinCluster node on the result. I can tell that they are duplicate skinCLusters because the mesh quadruple transforms on joint rotation, meaning that the verts are getting driven 4x from expected results.

As I said, this is only happening to 2 out of many meshes in the scene, and the same replication process is being run on every mesh.

Thanks for any help.

[eric_iwasakiS2ZTS]

I'm actually dealing with this exact issue right now as I am trying to write a FBX export selection script for a game engine...and I've verified my scene only has a single mesh, single, skinCluster, single bindPose, etc.   Do you also get an error message "The plug-in could not locate the following skin cluster elements: skinCluster1" when you try to import the FBX file?

[brentmc]

Are you able to provide a sample scene that reproduces the issue?

Thanks.

[eric_iwasakiS2ZTS]

I wouldn't be able to provide the scene I'm working with as an example, but I suspect I'm having a similar issue as the OP in that I'm writing a FBX export script to function within a game development pipeline...where I basically need to export a bound mesh and skeleton untethered from its animation rig.

My initial effort did successfully export the mesh and skeleton with only a single skinCluster, but the skeleton collapses...likely the result of how it was initially set up to work with the rig.  While I could restore the skeleton by going to bindPose in the resulting fbx file, I really wanted the export script to ensure the mesh and skeleton were already exported in a way that was ready to be sent to the game engine...and I suspected the rig's constraints and Maya joint features like offset parent matrix were to blame.   I modified my export script to remove the constraitns, bake the offset parent matrix back into the joint transformations, and update the bindPose, but that's when I started seeing the skinCluster explosion in the exported FBX file.  I now get 76 skinClusters in the resulting export.  If I move the joint for the leg even slightly the mesh starts rotating like crazy....

I should also add I can get around the problem by baking out a single animation frame, but then I'd still have to open up the resulting export, remove all of the animation channels, and then remove the rig to produce the game-ready fbx file ...so it would still be a two step process (albeit one I could handle in the same script).  

[bmagner888]

I can't provide a sample scene because the content is under an NDA.