I understand the durability of the plastic can be questionable, but so far we have survived. We have already competed at the Arkansas regional with no problems with the winch. Most of the parts were done with 15% fill and 4 layers. The ratchet hub which probably takes the most load was done with 5 layers, I can't remember if we increased the fill rate on that part. We did have a small part on another part of our robot break fortunately we took the 3D printer with us, and it was a part that only took about 30 minutes to print.
The winch is pulling in a web strap, and the launching force of the catapult arm is created by two of the 25 pound constant force springs from Vulcan. We can make a successful shot if we are around 10 feet or so from the wall. I think the amount of torque provided by the springs is about 650in-lbs, and due the angle that we are pulling, I think the maximum force exerted on the webbing is around 72 pounds when we initially start pulling but decreases from there as we pull it in.
With respect to the winch, the only part that broke during practice was the lead screw nut sheared off the head. This wasn't even a part we had printed. But it happened because we overdrove the lead screw. Since then we have had a couple of limit switches in place to keep that from happening again.
The parts have been uploaded to thingiverse:
http://www.thingiverse.com/thing:271463