The machine now rotates 130 degrees. I was hoping to get a full 180, however this isn’t possible due to the spacing between the pvc pipe and the threaded rod. When the stepper motor is off, there is some rotation of the gears which would cause the pen piece to move slightly, however when the stepper motor is on this should no longer be a problem.
The first half video shows the machine rotating at a constant speed, however this sort of movement will be uncommon, occurring only when a horizontal line is drawn across the arm. The second half of the video shows a more common stop-and-start movement which also shows the servo motor is strong enough to hold the machine at different angles.