The arm1 length adjustment should have a horizontally split overlap, not vertical, such that the bolts holding it together are put under tension by belt tension, not shear. It is easy for the two parts of arm1 to rotate WRT eachother if the bolts aren't done up extremely tight. This droops the arm down and could misalign the end of the arm with the optoswitches.
tjhowse
commented
4 years ago
The arm1 length adjustment should have a horizontally split overlap, not vertical, such that the bolts holding it together are put under tension by belt tension, not shear. It is easy for the two parts of arm1 to rotate WRT eachother if the bolts aren't done up extremely tight. This droops the arm down and could misalign the end of the arm with the optoswitches.