why do we need TWO axes now?
Well, if you'll remember with the single-axis, the angle in which the joint could move was VERY limited. Sure, you could trim away paper, but that leaves a very unsightly exposed area. This joint system allows itself to bend in at a perfect 180 degrees.
What this system allows is for the two axes to act as one large joint and perform a total of 180 degrees, more correctly simulating how far an arm or leg can bend.
Now that you understand the upgrade, please move onto Building the Example.