The central pivoting shaft is coaxial with the second stage idler pulley, and based on the bearing locations it looks like that shaft rotates with the pulleys. It's a self-destructing mechanism!
I'll be interested to see what the rest of the mechanism looks like, but from the renders we can only really tell that there are two wheels that go different speeds. Keep in mind that if these are indeed wheels for driving the robot, then the mechanism will have to be supporting a lot of weight. Make sure your parts are sized appropriately!