I know this is not as fun as making a new more durable servo arm, but what about just making a sturdy slam guard to protect the whole area?
Please excuse the crude paint interpretation of my idea, I just took a few minutes and I suck at it, but I think you get the idea.
The grey is a flat plate, perhaps 7075, perhaps thick Delrin, or I prefer UHMW (either one to keep it from hanging up)
Basically the yellow dots are your tie in points, the center one would tie into the upper link mount, the two on the right side would use spacers to reach the rear driver side servo mount screw, and the link mount area, giving you 3 solid mounting points that will not bend, and thus will protect your whole frontal area in a rock slam.
My logic behind this approach is that if you are going to slam a rock that hard that you might bend an arm, imagine what the transfer of energy is to the servo, and related gears, case etc. By making a more rigid - non bendable arm, you might be sending more force to the servo. Calculate the leverage at the end of the arm as it slams, which will be twisting or tweaking the out put gear. You may just crack the servo case, or worse. No big deal if you're just out practicing, but if that happened in a comp, well.. ya know. "thumbsup"
