Extruder randomly changes polarity

Hi there,
My Prusa i3 is running pretty nicely now thanks to the great people of this forum. However, I've got a weird problem with the extruder motor - each time I click extrude in Pronterface, the extruder motor changes direction. Any ideas why?
MarkR

... hmm ... maybe something with the assignment of the DIR-pin of the extruder?

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Viktor
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Each time? Is it very consistent, not random?

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Yvan

Singularity Machine

Sorry I should have been more clear. It alternates consistently when clicking "extrude", as in click once it rolls clockwise, click twice anticw, but when printing it appears to move randomly, though I'm sure there's some twisted logic beneath it all.

Maybe you're using "relative extrusion" vs. "absolute extrusion" and pronterface is expecting the opposite? Try sending an M82 (i.e. set extruder to absolute mode) or M83 (i.e. set extruder to relative mode) and see what happens. I believe most interfaces are set to use "absolute" mode by default, although I prefer "relative" mode. The slicer and host software have to know what mode you have it in though.

A quick test would be to hook your extruder stepper to the driver for one of the axises.

I had a tb6560 driver act like that and was fixed by replacing the driver. I had my board powered up running XYZ test and calibrations without a motor hooked up to the extruder driver.

Edited 1 time(s). Last edit at 01/05/2014 05:15PM by Dirty Steve.