You’re describing axis angle, quaternion is on another level of alien… https://www.youtube.com/watch?v=zjMuIxRvygQ
@calpgrmr no you can’t… all four components are used to describe a rotation. Always make sure the rotate order makes sense before animating. The “main” axis should be last : if the controller is meant to rotate on Y axis a lot, choose XZY or ZXY.
There’s still something you can do if you wan’t to keep animating using eulers instead of quaternions : bake movement to an empty (by constraining it to the animated controller then launching “bake action” operator), change the controller’s rotate order to euler, then constrain the controller to the empty (the opposite as before), and bake movement again. Of course your fcurves will be sampled every frame but I think there’s an operator to simplify curves. I haven’t used that in a while so can’t remember how it’s called