That is more of a general Unity question and this page has some useful resources:
The Ultimate Character Controller uses Unity’s Animator Controller to control all of its animations. The Animator Controller makes it extremely easy to replace the built-in . . .
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I am having a similar problem. I think while creating an animator is a general unity question indeed, more clarification is needed because it is not as simple as creating an animator with whatever transitions you want. This animator needs to work with UCC, which means working with all your parameters and inputs.
The linked doc describes how easy it is to simply replace animations in the demo controller, however as mentioned multiple times by your team, that is not recommended at all.
It would be very very helpful to have an overview of how to create a new animator controller that actually works. This is easy for third person perspectives as you can just kinda copy the demo controller, using the appropriate parameters to change values etc. The problems arise when trying to also match the first person arms to the animations.
I've watched the whole anim structure video three times now, and it does provide a good overview of the demo controller, but really offers no insight on editing this for your own purposes, or how to ensure that first person perspectives match. I think to sum this up perfectly, we want to see the workflow for adding a new animation, matching that to first person, etc.
A tutorial that is not just an overview of the asset, but rather how to use the asset separate from the demo, would be very much appreciated.