High Torque Arm design questions

[magnets]

As an offseason robot project, we're designing, and possibly building, a box-grabbing robot. We want to play around with some heavy lifting, and we were having some issues coming up with a strong pivot/bearing and drive mechanism for the arm and we were wondering what experience people have had with high torque mechanism.

Currently our goal is to make the maximum torque around 200+ ft-lbs.

This is in the ballpark of 2010 climbers. I've read through team 33's presentation of their hanger. I'm trying to find team 254's PDF as well as some pictures, which had some torque calculations and IIRC, material selection.
I'm looking at chains, belts, and gears.

The maximum tensile strength of 35 chain is 1,760 lb, so with a driven sprocket of PD (200/1760) = 1.36" it is AT the breaking point. It seems reasonable that a near 8" diameter sprocket would be safe (max size we can make easily). Is this right?

I've been told that chains can never handle this much torque, but I think that they can. For instance, my car, which maxes out at 150 ft-lbs of torque, at speeds a few hundred times faster than the robot's arm will go transmits all of its power from the torque converter to the input shaft of the transmission with a chain (or five ).


I've pretty much decided against belts. They're about 10 times weaker with working tensions than chain, and they'll probably slip unless I use a serious belt/massive sprocket, both of which are expensive.

I'm considering gears because I have tooling (7 pitch, 14.5* PA involute cutters) for it. It's really slow/boring to make these gears, so I plan on avoiding this if possible.

Any suggestions?