Welcome,
surprisingly there is not too much information on the cooperation between Houdini and Motion Builder. Could you share your knowledge? I have a character modeled in ZBrush, I just started auto rigging it in Houdini, but… how do I export the rig (skeleton at least) to Motion Builder? Or should I build skeleton in an other app? Or maybe should I import the model to Motion Builder first? And how about skinning then? Will the skeleton from MB read to Houdini for the weights to be painted? I am really lost here. Thank you in advance,
Artur

FBX is one route you may wish to explore.

Houdini and Houdini Indy support FBX import and export.
Houdini Apprentice only supports FBX import.

Import of FBX rigs also construct a geometry SOP network to do the skinning and deformation.

Thank you. So you suggest to use external skeleton built in MB, import an .FBX and do the skinning in Houdini? And what about muscle deformation then? Houdini Auto Rig offers nice Muscle deformation option, which bases all rig skinning on muscles not bones. Would that kind of binding of weights work on rigs imported from MB (I gues I would have to do an autorig and feed imported rig as an update rig, maybe?)

Skeleton built in MB should import in to Houdini via FBX. Along with the skin.

The bones will be in null<->bone_joint with a look at constraint a la Maya.

You can add muscles to the bones as the constraints to the muscle system. No issues there.

The auto-rig tools are a series of assets to construct an armature which then is used to author an Animation rig and Deformation rig. This is a custom set-up that won't translate over via FBX to Maya or Motion Builder.

The muscles use the Muscle Deform SOP to bind the skin to the muscles. This is a custom modifier not supported by Maya or Motion Builder. Therefore the muscles will not transfer out of Houdini via FBX.


I would pick the application that is to be used for:
- animation
- skinning/deformation

Animation is just channels and as long as names match up, should come over via FBX or as channels. May require a bit of hand work or scripting if you use Maya to do keyframe animation. Motion Builder should be able to export channels that can be imported in to Houdini CHOPs and applied to rigs procedurally and mix/match.

Skinning and Deformation can be done in Houdini and is probably dead locked there. Arguably it's the same in Maya as advanced deformers may not translate well in to Houdini.


Round-tripping of data between several applications still has a lot of hiccups. FBX between Autodesk products has it's own issues and is not a perfect solution. The common data format are the hierarchies and animation which does round-trip reasonably well though. It's the advance deformers (muscles, etc) that don't round-trip very well.

Best to dive in and start punting around MB, Maya and Houdini with a simple character.

Hope that helps.

Well, that helps a lot! Thank you. I think I make a skeleton in Motion Builder, export for weighting to Houdini (really nice tools here), and then export back to MB to do the actual animation, which I feed back to Houdini as the last step. The reason I am a little bit confused is that the auto rig tool seems pretty neat - it has eye controllers by default, for instance. And blending between FK/IK on-the-fly. But when I asked my friend- houdini veteran whether I should pick MB or Houdini for animating, he strongly suggested MB. I am a bit prejudiced to FBX format, since I have seen a lot of strange things happen to non-plotted animations after imports/exports. So my final question is: is auto rig any good for production pipeline?
Thank you again

I tried importing MB rig to houdini to align its skeleton with my model, paint weights and then export back to MB, but I ran into an issue. This nul->bone system you mentrioned causes Houdini cannot see a hierarchy of bones, unless I modify it by pinning bones directly to each other. Then nulls seems needles, but I cannot delete them, since they are targets for lookAt channel parameter. Is there a way to “rewire” this MB skeleton somehow, so that Houdini sees it as a fully fledged rig?

I made a skeleton in Houdini according to the naming scheme for Motion Builder. I imported it to MB and characterized successfully, but my weights are wrong and when I move/rotate joints, the character disappears. Anyone encountered that?

Just curious, I know its been a while but were you able to fix the weight and moving/rotation issue ?