Dough rounding machine inner workings

[Roctavio]

Hello, I have seen a machine that can round bread dough very easily and don't undestand how the movement is achieved.

Watch these videos please:

http://youtu.be/fFjovsZokcc
http://youtu.be/6gicSTS-nCo?t=13m35s
http://youtu.be/2VF_ipbpgAM?t=4m42s

As you can see, there are 2 drums that turn at the same time, one outer, one inner. The inner drum's movement is what I can't figure out. In my opinion it turns at the same rate and direction as the outer drum, but not only does that, also there is another movement, a "circular" movement around the longest axis, that moves the dough pieces around the edges of the outer drum.

My question is how that circular movement of the inner drum is produced?

 

[256bits]

Most likely the inner drum just moves back and forth, and the dough rotates due the combined motion of the inner drum and the rotation of the outer drum.