mdrVB6 wrote:Thanks Carl, that is basically what I figured. So I'm correct to be using it in the 20 V range. So when I hold the red probe on the trim pot and the black to ground, I'm measuring 0.25. I guess what I'm asking is what are the units on that measurement and where on my motor data sheet can I find the acceptable range? I think that is a current measurement. I know I can run the motor up to 2.0A but I don't want it nearly that high for an extruder. Is 0.25 a good place to start? Thanks.
You are measuring Vref, which is the reference voltage the stepper driver uses to work out how much current to pump through the motors. You are measuring it in volts (V), so 0.25 = 0.25V.
If your Vref is 0.25V, then according to the motor driver specification, your motor current is being controlled to 0.5A, which is probably a touch low for that motor. You have room to go up, which is good news!
The more current, the more motor torque (when stopped / moving slowly) - they're approximately proportional. The disadvantage of running the motors with super high current is the heat, noise, and in the case of the extruder, the moire pattern it will put into the side of your prints (the microstepping becomes uneven).
I'd suggest similar to ward - my method's a bit different though.
(1) Get the extruder all up to temp, filament installed as usual, etc.
(2) Free-air-extrude a few 100 mm's
(3) While it's running, turn the pot down until the extruder starts skipping (clunking, you should be able to see/feel it skip).
(4) Now turn it back up and listen for a groaning noise - it appears gradually, the louder the groaning the more moire you'll get in your prints, but the less likely a skip will be.
(5) Tune back and forth until you're happy with a smooth sound but consistently no skipping (it's a balance!).
(6) Check the voltage when you're done, I guess it's likely to be a bit higher than you have it currently, but hard to say!
The pololu DRV8825 module allows Vref adjustment approximately between 0V and 1.1V, which corresponds to 0A - 2.2A motor current. Your motor will be fine over this range (nothing is likely to happen suddenly if you slightly over-drive it for a short time), so don't be afraid of playing with the Vref pot to get a feel for it. Take some time, get to understand the sound, it kind of makes sense when you listen to it. Think of it like tuning a guitar. 
As for whether this causes your splitting issue, no idea haha.
SD3. Mk2b + glass, heated enclosure, GT2 belts, direct drive y shaft, linear bearings, bowden-feed E3D v5 w/ 0.9° stepper
Smoothieboard via Octoprint on RPi
