Actually, we were thinking something like
this, but with a claw attached via another shaft to the arm segment so as to be able to "dunk" the ball over the overpass. But that claw's linkage isn't my concern at the moment - I'm more worried about the primary joint (in the upper left corner of the picture).
That is to say, our planned arm is a two-stage articulated system with a total reach of about 8-9 vertical feet (for hurdling purposes), and the linkage in question is the primary joint of the arm (hence the reason for the large torque requirement).
I do believe that mounting the arm directly to the 60-tooth output sprocket is probably the best means of attachment, but I still do not know how big to make the shaft to which said sprocket is attached, or how to attach the sprocket to the shaft (we intend to use a
60-tooth IFI sprocket to attach to this high-torque arm, but the only keyed hubs that I can find are these
AndyMark ones, which seem grossly insufficient for this application).
The idea that a 6-pound claw at the end of maybe a 5-foot arm (30 ft-lbs.) bent a .5" solid steel shaft is a bit disturbing - it almost certainly rules out the 3/8" shaft in the middle of our assembly (which must take 28.5 ft-lbs.) unless we can find some funky alloys (or, God forbid, titanium, although if that is the only feasible avenue then we may well consider it).
I guess that I'm just looking for hard numbers here, or some way of calculating them.