2015-01-05 - RAMPS and stepper motors

my Prusa i3 uses RAMPS 1.4 for stepper drivers control. since the very beginning i had problems with OY axis. few days ago i started to break every print i was doing. fortunately for me Rafał was around. as he's highly experienced with electronics he said that stepper motor is holding too weak – that the stepper motor of this size (engine salvaged from some printer) should be very hard to rotate manually, when powered, yet this one can be turned pretty easily…

we did some digging through electronics' schematics over the net and we managed to find that stepper motor drives have power regulation. it is Vref-based current feedback. my regulating Vref, using this potentiometer:

one can adjust current, and therefor increase power to a particular stepper motor (each controller has its own pot.). adjusting the voltage from ~0.35V to ~4.5V made all the OY problems go away.