Maxscript: Constrain to Biped 1


So in 2016, I wrote a maxscript to constrain humanoid characters to 3ds Max bipeds for easier animation.  Every once and awhile, I get someone asking me for the script and some questions regarding it, so I decided to write a post about it for the future.

Here are two videos demonstrating how it works and its setup:


A quick summary:

  • What this script does:
    • Builds a biped, sizing it to fit a specified character
    • Uses Orientation Constraints to drive the original rig’s bones to the biped
  • What this script does NOT do:
    • Require new reskinning or transfer of the original rig’s skinning, which often causes issues.
    • Transfer .fbx animations — or any kinds for that matter — to the biped.  This is JUST for the rig itself.

Why?

Why write a script like this?  Well, for one I’m old-fashioned.  I’ve always liked the 3ds Max’s biped.  It’s not perfect, a little buggy; however, I’ve felt it gets the job done and has a lot of extra features — saving poses, postures, animations, etc. — that writing on my own would be rather time-consuming.  Additionally, exporting just the biped itself can be rather problematic as it sometimes moves bone objects, which causes issues with animation retargeting since that is focused more on rotation.  Since this original rig is preserved and only driven by Orientation Constraints from the biped, this is less of a problem.

Then, despite the fact other character creator tools such as Mixamo supplied rig to biped scripts, though scripts never quite worked as well as I would want, often deforming the original mesh or rig and causing unforeseen issues.

The Script

Firstly, you can download the script here.  Note, this script was written for 3ds Max 2016 but has also been tested in 2017.

Instructions

Unzip the downloaded file and run the .ms file.  You should then see the following window:

There are two columns.  The left column, Biped Bones,  is for all of the biped bones that’ll be created; the right column, Character Bones, is for the bones in the original rig.  Note, there are 2 neck bones and 3 spines in the left column; however, the 2nd neck joint and 3rd spine joint do not need to be defined and are prefaced with [IGNORE].  When this was written, it was for one specific rig that used 3 spine joints and 2 neck joints; however, since this caused issues with Unity, I decided to remove those; thus enabling it to work on more humanoid rigs.  Unity can now handle a 3rd spinal joint, but still doesn’t use a 2nd neck joint in its default, humanoid rigs.

To start populating the right column, click the row you want to define and then click the bone / node you’d like to associate with the biped bone.  It’s a bit tedious.  There are two buttons for saving and loading, Save Selection Set and Load Selection Set, respectively, that can help a bit.  If you know the names or they are named in a way that can be populated quickly through copy-and-paste, this can be done by saving a text file, updating it, and then reloading it.  In the .zip, there are two examples of these files; they are setup for use with iClone Character Creator 1 rigs.

Once the right column has been populated properly, the Validate Bones button will check to make sure the bone slots are all assigned.  This will also show a pop-up for any bones that are missing.  Warning:  This’ll generate a pop-up for every missing bone.  

If all bones have been signed, click the Build Biped button.  This will generate a biped that’ll match the size of the original rig.  You do not need to, but it is suggested to then rotate the biped as closely to the original rig.

Then, the Build Helper Rig button will create a new rig that is identical to the original rig except it’s bone orientation will match the biped’s, meaning the up, forward, and right axes will match the biped’s.  This is important for the next step.  Essentially, an early thought for this experiment was to:

  • Build a biped
  • Align the original rig to the biped

However, one of the big issues is that rigs and their bone rotations can come in a variety of orientations.  If you use 3ds Max’s default align too, arms will sometimes be rotated in strange positions.  The helper rig solves this by standing as the middleman between your original rig and the biped.  It’ll be the same size as your original rig but the bone’s will match the orientation of the biped.

Next there is the Align To Biped button.  This aligns the helper rig to the biped and then the original rig to the helper.  This is why aligning the biped to the original rig helps; otherwise the changes can look rather broken.  They are easy to fix because, again, this is just affecting rotation and not placement of the original rig.

The Create Constraint button is the final step.  All other steps should be completed first — including making backups in case there is an issue.  This will create Orientation Constraints between your original rig to the helper rig and from the helper rig to the biped.

Once this is done, the rig should now be driven by the biped.

Other Buttons & Tips

As you may note, there are two buttons I’ve yet to discuss, Quick Parent and Quick Child.  Quick Parent create a parent bone the selected bone’s parent and itself.  This would be used for something like a rig with only one spine.  This will create the second spine automatically that can be used in the rig.  Then, Quick Child, creates a joint at the end of a joint.  The biped rig requires 5 fingers as well say finger nubs, for example, and this button will create these quickly.

Another tip is that if you create a child, for something like the head nub, make sure that they are aligned perfectly vertically; otherwise, the head will be tilted when aligned to the biped.  The toes have a similar problem I haven’t quiet figured out, but again, aligning the created biped as closely to the original rig as possible will help resolve some misalignment issues.  Another tip is that instead of rotating the biped once it’s created, rotated the bones of the original rig to match the newly created biped as closely as possible.

Final Steps

After completing the steps, you can now animate just the biped as your would except you should NOT rotate the pelvis bone; this causes the hip and spine bones to translate slightly, causing issues upon export.  They will export fine, but your animations won’t match perfectly and when importing to Unity, you’ll get errors about how those bones have translation data and that said data will be ignored if it’s part of a humanoid avatar.

Also, don’t export everything; use the export selection and select only the original rig’s joints and/or any meshes you’d like to export.

Quick Summary

  • Unzip this file.
  • Run the BipedRigCreator.ms script in 3ds Max
  • Define the joints in the right column, creating children or parents where needed
  • Validate the bones
  • Build the biped
  • Build the helper rig
  • Align to the biped
  • BACKUP (if not already)
  • Create constraints

Wishlist

I’m unsure if I’ll add anything to this script anytime soon, but here is a list of things I’d like to do:

  • Streamline the bone selection or remove the left, right column idea as they aren’t lined up
  • Allow for multiple spine joints / make the correct number of spines based on the number of spine joints assigned)
  • Adjust errors for the head nub and foot nub issues
  • Not show a pop-up for every missing bone, but instead a list of all missing bones upon validation

Anyway, if you use the script, great!  I’d love to see what people do with it.  Again, I mostly wrote this so people who would like to use it in the future have something to refer to.


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One thought on “Maxscript: Constrain to Biped

  • Henrythejedi

    Hello, Mattrified
    Wow this script of yours is the most important script I have ever downloaded.
    I searched heaven and earth for the script to convert those damn good looking reallusion character creator models straight to 3d max biped and yours is THE ONLY ONE in the whole world to do just that.
    Man, keep up the good work
    The only concern I had is that my mesh moves around the elbows and shoulders when I click on the Align to Biped button(as you do in your Rig to Biped Demo at 4 minute 32 seconds)
    Is there a way to force my mesh to remain completely in position even after clicking the align to biped button
    and also, the toes on the biped, is there a way to add more toes(5 toes) to the script
    Thank you once again for such a truly life changing script