I have read the Wikipedia page on gimbal lock, and am still confused about the entire matter. My understanding is that, using a local coordinate system, if you rotate a model about its X axis then its Y and Z axes experience gimbal lock, and become "locked" together. However, my understanding is that if you rotate the X axis, then both the Y and Z axes rotate with it, and as such remain separate. Wikipedia, as always, while a good resource is difficult to understand on this topic. Could someone please endeavor to explain this to a person who does not have a Master's in physics or mathematics?
I gather that it's an inherent weakness of just storing three axial rotations (Quaternion, on the other hand, also evaluates orientation value).
(Per ideasman42's comment): We can easily see this for any object using Euler rotational system, by manipulating the rotation widget with transformation orientation set to Gimbal. It turns out to be easy to reproduce, by manipulating 2nd axis in the evaluation order (Z for XZY, or X for ZXY, etc.). I get the following condition on XYZ order by just manipulating Y axis:
First, I recommend looking at the Guerilla CG video that explains The Rotation Problem as it relates to 3d animation. This is important because it explains why Euler and Quaternion rotations are different. Unfortunately the only available copy has very poor A/V sync.
Cut to the chase in Part 2: Euler (gimbal lock) Explained