Thank you Chris! I found that if the J2 jog angle is small, say 10deg, the arm shaking is obvious. When the jog angle is large, the movement is smoother. Maybe the trajectory generated for a short motion is jerky. Later I will investigate how to generate a jerk bounded motion.

Hi Pierre, did you get feedback of the Teensy powering? I run into the same problem during wiring. Thanks! If both Teensy and Mega 2560 are powered by PC's USB, does it have same ground as the 5V PSU?

Thank you! I ordered from Arrow. Maybe I was lucky to get the last several. Today when I checked Arrow it became "Out of Stock" again...