I added a 9g RC servo to my 3D printer for tool change purposes. It actuates a latch that locks the parking extruder in place. You can see the servo in action in this video at around 30 seconds: https://www.reddit.com/r/3Dprinting/comments/q276ct/wip_prototype_of_my_asymmetric_semiparking_dual/
With a new servo everything works fine. But after a few prints, the servo starts jittering. After a few more, it starts flailing wildly between its extremes (as long as the servo is enabled, if disabled it stops) and after a few more prints after that, it will stop working all together.
I've tried 9g servos of different brands (I already destroyed two HXT900 from Hextronic and a MG90S from DIY MORE, which has metal gears). So I don't think it is a straight servo quality issue.
The voltage is regulated to a nice 5V, but on one servo I tired getting the jitter under control by regulating the voltage from 4.8V to 6.0V, with no change.
The servos are only active for around 20 seconds for each tool change, to reduce heat and wear. They get detached after that.
What could be causing the servos to fail like that? Am I using the wrong type of servo for the application?
I use the same servos on RC planes and never had any problems like that there. But then again, the 3D printer runs for much longer on the same servo than any of my RC planes ever did.
Edit: The problem only occurs while the servo is attached. While the servo is detached, it doesn't move at all, doesn't vibrate, hum or get hot.
The first servo died without the detaching. I only added the detaching after the first servo died. I am using a SKR v1.1 board with an LPC1768, which, for some reason, in Marlin doesn't use Hardware PWM. So the signal always jitters, which makes the servos hum, vibrate and get hot.
I don't think that the jitter is causing the wild flailing, since a fresh servo will always work fine, but after a few hours of printing, it will start twitching, which gets progressively worse until the servo permanently runs between its extremes while powered.