Example PC-Excellent FBT Taur Avatar - VRC Constraints

No script or anything--this is just an example for your reference of a working FBT taur rig using VRChat's new VRC Constraints! At time of posting, they were still in beta, but nearly finalized.

This rig is magnificently simple, compared to what I had to do before to fake reverse rotation with classic constraints. (Though, back then I didn't know about setting a parent transform's scale to -1...) 

There are ONLY TWO ANIMATION CONTROLLER LAYERS driving this taur! And only two Phys Bone components! And only two Contact components!

This rig can be simplified even further if you are an experienced user, but there is a minor impact to function. You can get it down to one Contact Receiver and one PhysBone, by replacing the existing HindCrossBOOL Contact&Receiver setup with a single large Contact Receiver on your left foot, which Receives "FootR" from your right foot. Use this float value to decide when your feet are far enough apart that you want to toggle your hind gait to "Same-Side Mode." Then, delete the "ParentConstraintXYYZ/HindSpinBone" transforms, and change the parameters used inside the "Opposite Blendtree" and "Same-Side Blendtree" gait states to piggyback off Spin_Angle instead (instead of their native HindSpin_Angle). 

If you use "the distance of your Humanoid feet apart" to drive the hind gait toggle this way, it will sometimes kick off when your feet are far apart from e.g. taking a big step forward, which shouldn't really trigger that mode... though there is a "Locomotion Detected" kickout from Any State to help with running around. 

If you use Spin_Angle instead of HindSpin_Angle from a separate Phys Bone on the butt to decide when you're spinning enough to take catch-up steps, you'll need to tweak the Phys settings on Spin_Angle, probably, and just overall tweak everything it's controlling (at the Source Weight animation level on the damped rotation constraint) to find a good compromise between detecting spin for stepping, and responding to spin by tightening up the damped rotation constraint. 

BUT your reward will be an extra Phys Bone Component and Contact Component to use for YOUR purposes, while remaining PC Excellent in your FULL BODY TAUR (or quad)!!