problem: Eyes constraint works well, but when I rotate the eyes, the aim becomes weird, it rotates by itself in it's local axis and sometimes it flips.
images:
solution:
-aim vector: the direction that the local axis of the constrained object will point at (in this case, the locator is in Z direction, so put 1 on Z)
-up vector: a vector that works with the aim vector to control the orientation of a constrained object. From the range of my knowledge, this is normally will point to the locator as well to avoid the flip. so in this case, put 1 on Z as well. because when you rotate the eye,
-world up vector: this one determines the scene's world up, which is Y, so put 1 into Y.
By default, up vector and world up vector would have the same value, meaning they'll stay aligned as close as possible. that's why when you rotate to the extreme degree, sometimes maya don't know which to calculate and give flip result, or double rotation, because of double orientation.
p.s: I don't really understand about this one, so please anyone, correct me if I'm wrong. :)