X and Y Sensor Flag Deformation Can Cause Erratic Motion Control & Crashes
The X and Y endstops provide origin coordinates to the controller so it can keep track of where the head is. When you power on the machine, the head automatically moves to the home position which also happens to be 0,0. When the axes trigger their respective optical sensor, the controller acknowledges and sets the 0 coordinate for each axis. If the controller does not receive the information from the endstops the machine can behave erratically and/or become damaged. Sometimes these sensor flags can get out of alignment and contact the sensor. It is important to check, adjust, and tighten the X and Y sensor flags periodically and make sure they actuate the optical sensor without making physical contact with the sensor. It is important to note that these sensor flags can break if bent too far or too many times.
Here is an example of a failed Y-axis sensor flag:
And here is a short video on this topic: