Extruder failure after a while of printing

Hey guys, well I seem to have a problem with my extruder.
I've been trying to print test cubes and the resolution is looking pretty good, but I havn't been able to print a whole cube yet. It prints about 25-30% of the 20mm cube and then the extruder stepper just clicks back and forth. It just oscillates back and forth making a pretty big racket, as the rest of the steppers continue to work.
If I remove the motor from the extruder, I can get it to go without any load on it, but anytime I put a little load on it like rubbing my finger on it, it just starts shaking back and forth like before.
I replaced the stepper driver and it did the exact same thing. It printed about 30%, then freaked out. Now I'm scared I'm burning up these drivers...
I'm working with ramps 1.4 and E3D stepper drivers. The motors are Minebea Nema 17's with 1.8 step angles. I have both the stepper current and resolution (quietness?) potentiometers on each driver at around the halfway point.
Like I said, works well until it just doesn't. Anybody ever run into this?

sounds like your steppers are stalling, and you have to figure out why, when they stall can you reverse the plastic out.?

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Yes, I can reverse the direction, but sometimes when I hit the reverse button it goes forward instead, like it can't make up it's mind. Are my drivers in danger of being damaged? Or could they be the causeof the problem? I've read on other forums that to stop steppers from stalling the reduce the speed, but seeing as this is the extruder, I can't really do that...

It could be a under current issue.Have you properly adjusted the current on the pololu driver? Turn the little pot counter clockwise while jogging the stepper until it jitters or stops then go clockwise 1/8 or 1/4 turn until it is working well. I have seen that jitter when my connector vibrated off of the ramps board and was barely connected, you might check the wires.

I did not see a mention of a heat sink on the pololu drivers. do you have heatsinks and a fan on them?

If you are going to mess with the current settings, get a volt meter. Measure the voltages on the Vref. Monitor them while you are trying to set them. These tiny little pots are not very precise. It's very difficult to get them where you need them by bumping them up and down.

I posted this in another thread but I'm having the same issue. I'm using repetier host. During a print the extrude goes the right direction but the retract goes the wrong direction causing it to stall as it is forcing too much plastic to extrude. When working in manual mode, extrude goes extrude, but once you hit retract it goes the wrong direction for a little bit before starting to retract. then when you press retract once again it goes the right direction. it always seems to make this error when going from extrude to retract, not the other way around. I tested all of this with no load on the motor, switched out my axis motors that work fine, changed the vref to an acceptable level of 0.3v.

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If your motors actually turn backwards, that's not a good thing. It suggests that they either are defective or the driver board is blown.

I tested other motors and it's doing the same thing, so I don't think it is a motor issue. I also swapped out the driver board with one of the axis boards that works properly, same problem. seems very odd

I was monitoring pin 9 on the drivers which is the dir pin. on axis x y z, moving 1 direction it is ~0v changing the other direction it is about 5v. but on the extruder its either 0v or 2v. does this sound right? I am assuming the dir pin needs either 0v or 5v not 2v which is maybe why it is hesitant on changing direction

UPDATE:

I started to trace back to see why it is getting 2v instead of 5v. turns out it was being shorted by a pin right next it in the MCU. i carefully took a sharp knife and removed the excess solder and now it seems to be working

Edited 3 time(s). Last edit at 12/27/2013 01:14AM by vinhdinh.