I'm building Gael Langevin's robot arm from inmoov.fr, which has a few servo motors with circular control horns that control the string "tendons" of the fingers. The strings are tied very tightly so that they can fully contract and extend the fingers. I've noticed that over time as the fingers open and close, the screw holding the servo horn in place begins to loosen, the strings slacken, and the fingers lose their full range of motion. Is it because the strings are tied too tightly, or something else? I'm about to superglue the screws into place...
On the servos I have the control arms have a splined socket that fits over a splined shaft on the servo so the screw should not be subject to any rotational loads.
If your servo shaft is metal with a machine screw holding the arm (rather than a self-tapping screw into a plastic shaft) then it may loosen with vibration. If that is the cause I suggest trying some glue, but only use superglue as a last resort as you might never get the screw out again. I would try EvoStik contact adhesive.
Thank you for the advice! Yeah the servos I have are just regular screws with no splines, that sounds like a great design addition... I guess I'll just go for the super glue lol