I added the binder clip in.  Well, combining the thinner parts with how strong the binder clip is flexes the shell now.

I modeled 4 different spring tensions into the lever arm and base plate as 8 sets of holes. The closer you get to the pivot, the less applied force.  All of them are way too strong.

So, I need to change that, beef things back up a bit, and still stay thin or at least stay out of the tape path.

Secondly, my choice of using gravity to engage the ratchet arms is not reliable. The attachment to the lever arm as modeled is a pin, which grabs in the socket on the arm.  It would probably work fine if it weighed more than a gram, but it doesn't. 

It all amounts to it only works... sometimes.

The way I see it I have two choices for the ratchets.  Add an actual spring of some sort, or model a 3D printed spring and build the lever arm and ratchets as one piece.  I toyed with the latter already and it works, but accuracy is not as good.

Working on it.