Quote Originally Posted by kd7eir View Post
I fought that demon myself for quite a while. /dev/tty/ACM0 only appears when the Pi can see the RAMPS via USB. Not sure what causes it to not detect it at times. Restarting OctoPrint seems to resolve it most times, occasionally I have had to reboot the Pi itself.
I used to struggle with this as well as a number of other seemingly random instabilities. I think the 5v regulator on the Arduino isn't really up to the task. With RAMPS and the LCD, it's very close to what it can handle--even on the Taurino Power. Adding a servo to the 5v rail caused me all kinds of instability. In the end, I cutt D1 off the RAMPS board and supplied 5v from the power supply to the +5v and VCC pins (no jumper) as well as to the Raspberry Pi through the GPIO pins, all with separate runs back to the power supply. This fixed pretty much all of the random symptoms I was having, including Octopi falling to start on boot and the Pi crashing or rebooting mid print.