I had another servo failure today, after a lot of walking around and showing the robot off. I'm seeing an interesting pattern. It's always the two servos which move the rear legs horizontally which fail. These seem to be under the most strain, being the servos responsible for most of the forward/upward movement of the robot with each step. Surprisingly enough, the gears are not failing at all. The cases are. The mounting tabs which connect the servos to the robot chassis have cracked on two servos now. I am also seeing failure of the case at the point where the gear shafts are held in place. Over time the shafts wear away the plastic until the shafts can wobble enough for the gears to jam or come unmeshed.
I have seem this type of failure before. Now that the problems with stripped gears appear to be solved it seems the plastic servo case is the next weak link. I have some ideas for reinforcing the servos but the machining involved may beyond the capabilities of my workshop.