Extruder motor stops turning midway through print

I have a Makerfarm v2 Prusa (Printrboard, Marlin firmware, Pronterface) using Greg's extruder and a NEMA 17 motor. Every single time so far, the extruder has stopped moving in the middle of the print process. I set the pot for the extruder at 4 o'clock -- less than that the motor will seize and more than that, it will heat up much quicker.

The hotend is 3 mm and I'm using ABS and I'm wondering if the motor just doesn't have enough torque after building up back EMF or if I'm just doing something wrong.

I've done the following tests:

- During a print, I'll watch until it appears that the extruder gears are no longer turning. I'll then pause the print, move the hotend to a different spot, and extrude manually. Result: The extruder will still seize.
- Then I try retracting and "extruding" less than the retraction distance. Result: The extruder will not seize.
- Then I try extruding up to the calculated point where I know the extruder would be beginning to force the filament through the hotend. Result: The extruder, again, will seize.
- I've tried adjusting the pot at *this* point and repeating, with no discernable effect.
- I will keep the print paused, go away for a long time, come back, and restart. Result: The extruder will operate normally again, much like it did when it first started, of course, with inconsistencies in the print.

Temperature of hotend, 235C, of bed, 135C.

I'm using this power supply. The drop in power does seem to correlate with the temperature of the extruder motor.

Any suggestions? I am at a loss.

1st, turn your motors off and make sure you can extrude by hand. Unplug E motor if you can figure out how to turn them off. Mine are generally off when I turn the printer on. You will need extruder to temp before trying.

[Edit] I realize these are instructions for ramps, but they should be modifiable to printrboard. Math may be different.[/edit]

Rather than relying on pot position and motor behavior, I would recommend you use the v-ref method. This page needs a more descriptive less mathematical description, but the general idea is:

You will need a voltage meeter capable of measuring < 1 volt DC.
Position probes as show and measure voltage.
Adjust pot in tiny increments until the desired voltage is obtained.

Start out at 0.4 volts and work your way from there. My motors never run hot. They don't even really get warm.

I don't know if printrboard supports a second power supply, but my printer still had bugs after all kinds of tuning. They didn't all go away until I added a second PC power supply.

Edited 1 time(s). Last edit at 08/13/2013 12:08PM by appdev007.