https://sims4studio.com/thread/466/blender-create-sims-absolute-beginners
Introduction
This tutorial will show you the way to use Blender to make a CAS pose for Sims 4. It is not exhaustive so if there's something you want to know about the process that isn't here please post in the thread and I'll add it to this tutorial.
What you will need
Sims 4 Studio
Blender 2.70
Making your animation clone
All poses are animations. They can be as simple as a single frame but for the type of pose used in CAS you will probably want it to be longer. I covered how to make the animation clone in my other pose tutorial so I'm not going to repost the pictures here. The basic process is as follows:
Open Sims 4 Studio and select Create Animation.
When the next screen comes up type the word trait into the search line.
When the pop up appears give your .package a unique name and click Save. Good names include your creator name and the name of the trait the pose will override.
The next screen will come up and you will see three buttons on the right hand side. Click the one that says Create New.
When the pop up box appears enter the name you want the .blend to have. This can be the same as the name you gave the .package if you want.
Once you've saved the .blend open Blender and open the .blend you just saved.
Rotating Joints and Moving the Model
b_ROOT_bind__ line. If you want a motion to affect the entire model this is the joint to use. You can select it by just clicking on this line.