[sanddrag]

The shaft would be exntended, no hanging in mid air.

I don't actually plan to build this thing, but if I did here's a few things I would do.

Actuation: Not really sure but I'm thinking pneumatics for speed and strength. Might try multipositioning but maybe just use two cylinders in series.

Gears: Might try 3/8" wide to save space, but 1/2" is probably a safer bet. 20 pitch seems to work well and be readily available. I suppose beveling the edges a little bit would aid in meshing, probably adding a couple thousandths in the c-c distance would as well. Other than that, I wouldn't match speeds or anything, it should be fine

Any more comments/ideas?