I am in the process of building my first CNC router. I am using an Arduino UNO with a CNC shield V3. I am using A4988 Motor Drivers and some NEMA 23 motors salvaged from a printer. The motors are running off of 24VDC. The Arduino is running GRBL 0.8c and I am using GRBL controller software and Universal GCODE sender.

The problem I am having is I can jog the motors, but sometimes they will randomly switch directions.I don't know what is going on.