FBX to Biped : There and Back Again

Convert HIK FBX to Autodesk 3dsMax Biped

How to match the 3ds Max Biped to your custom skeleton for easy sharing of rigs, animation and better retargeting in MotionBuilder.

Use Case:
You Have a character rigged for Unreal with custom joint locations using the ART rig. You also have existing animations that are in Max and Maya and you need to have people use Biped to animate.
Biped is a GIANT pain to fit to other skeletons… so this handy guide will help you out.

Part 1:

Use the #Autodesk Character Generator to create a file and download for max. In the zip there is a script that will build a Biped that matches the skeleton. We tried a few variations of existing scripts and custom tools but they all had issues, this is the best choice for speed and getting a good end result.

Autodesk Character Generator download settings to get the Maxscript

Part 2

Next import the Character Generator FBX skeleton you downloaded and align it to your custom skeleton. We did this in Maya since that was where our source skeleton came from.
We aligned position and used IK to rotate the joints so they stayed clean, then froze transformations to clear the skeleton of rotation values. (this puts the rotation into the joint orient)
Then mirror the FBX skeleton joints so you don’t do twice the work, and be sure to replace the _L for _R.
Export the FBX skeleton back out to .FBX and then import into #3dsmax

Align the FBX skeleton to your own custom skeleton

At this point we don’t care if they are a one to one match because we can adjust the Biped structure/bone count after it is created, we just need the major joints to align and the fingers!!

Part 3:

Import the exported aligned .FBX file in to Max
Open the free script CharacterGenerator_FbxToBiped.ms from your Character Generator download zip file that will convert the skeleton to a Biped.
Run it and the FBX skeleton gets replaced with a matching Biped, that we then edited in FIGURE mode to add prop, twist bones and adjust neck count.
Note we placed a marker at the head and then had to snap the Biped Head back to where it was after changing the neck count, since the head moves when the bone count changes 🙁
Now save off a .FIG file so that anyone that needs to can create a Biped that matches your custom skeleton.

*The hip joints in Biped don’t like to move so some manual adjustment might be needed to align hips and feet but it is minimal and easy to snap the ankles to the correct location. Just double check against your source skeleton.

MotionBuilder or Maya HIK retargeting:

If you need to retarget existing FBX moves onto the character, from Max, Export this new biped as .FBX and you can characterize it in MotionBuilder. From there you can retarget animation onto it, then save that motion back to FBX and import that motion with file Import directly onto the Biped skeleton. This will bypass the Biped mocap import/BVH process because it is very limited and destroys the motion quality AND makes everything harder. By staying in FBX the entire way and you will have a Custom Biped that has full motion capture ready to save out or animate in #3dsmax and stay in sync with anyone using Maya or MotionBuilder to animate with.

Final step after loading into Max is run the script that builds the Biped


Part 1: Custom Biped skeleton for MotionCapture retargeting and animation in #3dsmax from #Maya or #MotionBuilder

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