Z-axis steps or Extruder steps wrong?

Hey guys,
I started having an odd error recently, my z-steps seem to get shorter as I print. Notice in the image the small lip, that was caused by the extruder nozzle "pushing" into the layer below...smooshing it. As you can see the print starts out fine, but ends up smooshing my layers (i killed the print when I noticed this happening as it just gets worse the longer it prints). I re-calibrated both Z-axis steps and Extruder steps, both are right on the money. The only thing I changed recently was I replace a "cheapo" stepstick from China with a nice DRV8825 from Pololu.com. I replace the Z-axis stepstick so that's the obvious culprit, but how can I be certain? At first it wouldn't even work, then I turned it upside down (perhaps printing was wrong on stepstick). The everything seems to work okay... except for the problem I described above.

I really appreciate any suggestions and help on this one as I've hit a road block and I'm a noobie; don't wanna mess with the microstepping/pots if I can avoid it (nor do I really know how).

Prusa i3 from Replekio (they suck)
RAMPS / Atmega 2560
Repetier-Host V1.5.6

thank you!!!

You know, the drv8825 has 1/32 instead of 1/16 microstepping when you leave all the jumpers plugged? You have to adjust the z-steps/mm by factor 2...
The easiest way to do this, is connecting the controller to pronterfac and check the echo lines for: M92 X... Y... Z... E....

Then send : M92 Z( twice the actual value) followed by M500 to store it in EEprom

-Olaf

Thanks Olaf,
I will record your notes and look to them if I ever re-enable my EEPROM (i disabled it because it was only way I could get this darn thing working... like i said, i'm very new to this). I'm scared to touch EEPROM because I got this thing printing pretty good right now, but I know i'll have to that sooner or later if I want a better printing experience.

My problem was much simpler to solve, it was overheating. The DVR8825 runs very hot (tech support at Pololu said I didn't need a heat sink, i guess he was wrong.)... I ripped out a 120mm fan from an old computer and focused it right on my board, that did it; print came out great.(duh!) Although, I put my laser temp reader on it ran up to about 120F. I'm not an electrician or engineer, but that seems too hot? My "cheapo" stepsticks we're all under 100F.

Maybe I can barter my services; get help with my firmware settings and I will model parts/objects in exchange? Na... prolly a thousand 3d modelers on this forum.

Thanks again, Olaf!
- Richi

Quote
PixelPusher
My problem was much simpler to solve, it was overheating. The DVR8825 runs very hot (tech support at Pololu said I didn't need a heat sink, i guess he was wrong.)... I ripped out a 120mm fan from an old computer and focused it right on my board, that did it; print came out great.(duh!) Although, I put my laser temp reader on it ran up to about 120F. I'm not an electrician or engineer, but that seems too hot? My "cheapo" stepsticks we're all under 100F.

DRV8825s should run cooler than A4988s at the same motor current. However, I think some DRV8825 drivers use 0.05 ohm sense resistors instead of the 0.1 ohm sense resistors used by cheap A4988 drivers. So if you are using the same Vref, you may be running them at double the current.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

You can also write the M92 Zxx.xx line in the startcode of the slicer if you don't want/have EEprom.

dc42 is right, you have to adjust Vref, when the drv8825 get's so hot. That's not rocket science.
-Olaf