Video: From FBX to CAT Rig With Skin Transfer (3ds Max)
Hey, fellow animators, I’m Miloš Černý. Let’s first summarize what we actually want to achieve in this tutorial. I have an .fbx file here, with a deer model. When you import an .fbx with a previously rigged model into the 3d software, it will most likely look something like this. It has all the bones and the model is still skinned properly. But you can see it doesn’t have an information about it’s rig anymore. And therefore, you are not able to do any reasonable animating with it. I bet you have already experienced a situation like this. Maybe you have downloaded some .fbx on the internet, maybe you needed to get a rigged model from Maya to 3ds Max, maybe you have just lost a file with the initial rig. It doesn’t matter. Sooner or later you will probably get into a situation like this. So what do we want to achieve then? We want to rebuild a rig for this deer with exactly the same bones and skin as it was before.
And because you are on my channel, we will do a CAT rig of course. A little side not here. If you get these horrible bounding boxes around the bones and you don’t want them, just head to Customize, Preferences, Animation tab and switch Key Bracket Display to None. Ok, so basically what we need to do is a fresh CAT rig from scratch. But a big help for us is, that we will use the existing bones as guides of where we need to place the pivots of the new bones. So create a CAT Parent and a Pelvis. Align the new Pelvis to the old one and of course, always make sure, you have all the axis selected for both position and rotation and also Pivot points for both objects. Now, I know that I always tell you to resize the bones properly so they match the model as best as they can, for skinning. But here it doesn’t make any difference, because we have the skin already done and we will just transfer it to this new rig. So in this case, the size of the bones doesn’t really matter. Now a spoiler alert, we will have to do this alignment for all the bones. So a pretty repetitive task but it usually only really takes a few minutes.
I will show you how I will do one Leg and then will probably speed up the rest of the process. Start aligning the IK platform first. If you don’t have any reference bone for the IK platforms in your .fbx file, don’t worry. Just place the platform manually to the place where it fits the model. Do the ankle after that, and then align rest of the bones from top to bottom. The shortcut for Align is Alt+A by default. That one will be pretty useful for this. Sometimes the bones need more then one alignment because of the IK. You could switch to FK though and align them that way to make sure they are on their places precisely. Here I didn’t think it’s necessary however. Ok so now I will speed this up as I said. If you don’t know how to build a fresh CAT rig for a quadruped, you can check one of my older videos, or even my recent Dino-Bird series. Both are linked below the video as well. After we are done with this new CAT rig we will transfer the skin from the old one to this one. So stay tuned.
However this doesn’t take too long. The whole process took me only something about 5 minutes. This is a very simple rig though. Ok, we are done. Now to the more important and less known part. Transfering the skin. First I want to say though, this actually has nothing to do with CAT anymore. It’s a 3ds Max feature and can be used for any skin and any bones. So we have a new rig done with all the bones renamed as well. Let’s select it and put it into a new layer to keep order in our file. It’s pretty important here, because here we can not get lost in the namings. You can see I have two layers with rigs, one with the old one and one with the new one. Now if we try to animate with the new rig, it of course doesn’t move the mesh, because the mesh is still skinned on the old one. So we need to transfer the skin between them.
The mesh has the skin modifier but we can not just delete it and add the new bones because that will basically just destroy the skin and apply a basic one. What we need to do is to go to the last ‘Utilities’ panel, go to ‘More…’ and find ‘SkinUtilities’. These two buttons will appear. Now with the mesh selected hit ‘Extract Skin Data To Mesh’. It will create this new mesh object with ‘SkinData’ in it’s name. And it basically has all the skin values saved in the that mesh. They are two separate objects. Now we need to select our main mesh and we can just delete the Skin modifier from it completely. Because we have all the data saved in that new object. Now if you select both meshes at once and go to Utilities Panel again to import the skin, nothing will happen. That’s because the main mesh has to have a skin modifier with bones in it. So let’s do that. Make sure you have the right one selected and apply a Skin modifier. Hit Add bones, and add all the bones from the new rig.
Again, make sure you are selecting the right bones. That’s why it’s important to keep order in your file when doing this. Now when you select both meshes and hit Import Skin Data, this window will appear. Here you basically just need to pair all the bones to their counterparts one-by-one. You can do Match By Name if you have the names identical, but here it doesn’t work for me as you can see. I could just delete the CATRig part from the Target Bones if I wanted, but I wanted to show you that you can do it manually as well without any problems. After you are done with all the bones just hit ok and you are done. The new rig affects the model now, not the old one. You can actually delete all the unnecessary parts now. SkinData mesh, as well as the old rig. Now everything is finished. You have your CAT rig for animation and it exactly matches the bone placement and skin from the .fbx file you had. You can now create new animation layers and animate whatever you need. A lot of people asked for this video and I was finally able to make it, so I hope you liked it. Thank You to all my Patreons and if you enjoy my channel, subscribe, like and comment.
See you in a next video. I am Miloš Černý and Thank You for watching..