Drivers don't see the final rotation of a constraint. How to get copied rotation instead of (0,0,0)? The Premise:
Say you have a driver on Bone A that makes it's rotation = 50% of the rotation of Bone B.
Bone B has a copy rotation constraint to copy Bone C's rotation.
My expectation would be that Bone A's rotation would be 50% of Bone C's rotation.
The problem:
Bone A does not rotate at all because the driving rotation property on Bone B still shows as 0, 0, 0 even though Bone B has visibly copied the rotation of Bone C.
How would I get a driver to see the final rotation of a bone after applying it's constraints?
EDIT: A tangential part of my problem was I was using the &quot;RNA&quot; &quot;Single Property&quot; for the driver, but by switching to &quot;(x) Transform Channel&quot; I can then specify local space and get the result I want.
Let's reproduce the issue: two cubes, one copying the rotation of the other using a constraint. Each cube has a Suzanne copying the rotation of the cube in front of it, using a driver.

the driver for &quot;sleeping&quot; Suzanne:

Changing its type to Scripted Expression, default variable type to  Transform Channel and the property type to the rotation axis of your interest: