In my last post I pointed to the RPi as the reason why I couldn't get the same smooth servo action as with the previous prototype.
It's a poor carpenter who blames his tools.
Today I went back and looked at the code and it turns out the real culprit was my shoddy middle-of-the-night programming. I've fixed the Python script and now the stutter is gone and everything runs much smoother. I also fixed a bug in the turning sequence which made the turning radius much wider than it needed to be.
This time around LB-312 struggles a bit when walking in reverse. That seems to be a mechanical problem. I tried to add some lithium grease to the gears but that didn't seem to improve things. A possible cause is that the load is unbalanced.
Or maybe I need to take another look at the code.