1 Topic by brucesdad13 (edited by brucesdad13 2016-11-10 16:05:53)

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Topic: Pololu DRV8825 for Extruder

I purchased and installed a Pololu DRV8825 onto my Sang board on my SD2. I set the Vref based on this Soliforum post at 0.2. I didn't have to change the steps/mm in Repetier (or more correctly when I changed it was extruding double so I set it back). I know this is a drop-in type replacement for the stock A4988 driver. I left the three jumpers in place. Is mine working at 1/32 or is it still in 1/16 mode? I also seem to be reading that the Vref should be 0.5V.

I read on the replacement parts post that the stock SD2 motor is rated at 1.3A so perhaps 0.6 VRef would be better.... running at 0.2 VRef I've had seemingly fine prints and when printing 0.5mm layer height everything is nearly perfectly smooth. Anyone else have a DRV8825 for their extruder? The impetus was to eliminate Moire pattern...

http://soliforum.com/i/?NctKKSd.jpg

References
https://www.pololu.com/product/2133
http://www.soliforum.com/topic/2817/ste … ref-chart/
http://www.instructables.com/id/Install … -on-RAMPS/
http://reprap.org/wiki/A4988_vs_DRV8825 … ver_Boards

Edit:
Also read http://cabristor.blogspot.com/2015/02/d … steps.html My power supply is 12V. I'm thinking of trying the fast decay mode... well actually first I will set Vref to 0.5V and try that and then thinking of trying Fast Decay.

SD2 Pro + RH + Slic3r on Win7Ent (~Craigslist Oct. 2016 my 1st printer: upgrading & calibrating to near perfection)
- E3D V6 hotend; 30A PSU; Glass bed for ABS or Blue Tape on glass for PLA
- X-axis NEMA 14 press on fan (thing:1871741); Lawsy almost everything else; 3mm Z axis rod (thing:1868824)
- Sang board w/all headers, ATmega1284P w/OptiBoot and Marlin beta firmware; VRef tuned

brucesdad13's Website

2 Reply by heartless (edited by heartless 2016-11-11 00:35:38)

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Re: Pololu DRV8825 for Extruder

I am not 100% positive on the Sang board, but I believe that all 3 jumpers in place would indeed be 1/32.

dont get so hung up an the actual number for vref. on the extruder.
What I like to do is start a tall, single wall cube and tweak the vref until it is feeding well (not skipping steps), but does not have moire (the diagonal banding caused by the electrical pulses of the motor)

and tiny increments can have a big impact, so go easy. wink

SD4 #1 & #2 - Lawsy carriages, E3D v6, Rumba controller board, mirror bed plate, X motor fan, upgraded PSU & Mica bed heater
SD4 #3 - in the works ~ Folgertech FT-5, rev 1
Printit Industries Beta Tester - Horizon H1

3 Reply by Edwin

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Re: Pololu DRV8825 for Extruder

I have some DRV8825 in my printer. If all three jumpers are set, they will run on 32 steps.
Otherwise, I run this at 0.65 to 0.85V at the vrev. How many can be adjusted depends on the cooling, which one should have anyway to cool the board.

4 Reply by carl_m1968

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Re: Pololu DRV8825 for Extruder

On the 8825 vref directly converts to current. So . 85 would be . 85 amps.   1.2 would be 1.2 amps to the motor and so on.  It will be different for every printer and every axis. Also it is probably a bad idea to mix driver types.  I personally use only 8825 drivers as I think they are superior.

Printing since 2009 and still love it!
Anycubic 4MAX best $225 ever invested.
Voxelabs Proxima SLA. 6 inch 2k Mono LCD.
Anycubic Predator, massive Delta machine. 450 x 370 print envelope.

5 Reply by IanJohnson

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Re: Pololu DRV8825 for Extruder

I had better luck setting the vref by ear.  Set the extruder speed to something very low, like 10 or 5 and manually extrude some filament.  It will be slow enough that the sound will be pulsing rather than humming, making it easier to hear the difference the vref makes in the performance of the motor.  Turn the vref pot back and forth, and settle into the spot that gives the smoothest sound.

1/32 microstepping will eliminate moire, but it can make it worse when you first install the driver, until you tune the vref.  You can go by the voltmeter reading and recommendations, but in the end the right setting will depend on the actual performance of the driver, motor, printer.

6 Reply by brucesdad13

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Re: Pololu DRV8825 for Extruder

Thanks all. It seems to be working well now. I also did the fast decay hack and not really sure if that made much difference but whatever. Still banging my head against the wall. Moire is gone and a 20mm single wall test cube looks great at 0.05mm layer height. I tightened up all the carriages and so forth and installed the cable chain. I'm still having some issues here and there and if I'm interpreting it right could it be temperature? Most noticeable at the top of the part is some rather ugly looking and offset layers. The lower portion of this squirrel printed good but where it moves to infill there's thin indent line... this was 0.2mm layer height and 5% infill.

http://soliforum.com/i/?VIh5nyZ.jpg

It's a print of this: http://www.thingiverse.com/thing:11705

SD2 Pro + RH + Slic3r on Win7Ent (~Craigslist Oct. 2016 my 1st printer: upgrading & calibrating to near perfection)
- E3D V6 hotend; 30A PSU; Glass bed for ABS or Blue Tape on glass for PLA
- X-axis NEMA 14 press on fan (thing:1871741); Lawsy almost everything else; 3mm Z axis rod (thing:1868824)
- Sang board w/all headers, ATmega1284P w/OptiBoot and Marlin beta firmware; VRef tuned

brucesdad13's Website

7 Reply by heartless (edited by heartless 2016-11-12 02:15:54)

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Re: Pololu DRV8825 for Extruder

could be temperature, could be filament drag, could be a lot of things... it is so hard to diagnose over the internet. tongue

overall, the little guy looks pretty darn good, except for the couple of lines you already noted...

when printing, keep an eye on the temp graph - if you are getting a lot of fluctuation you may want to do a PID tune to stabilize the temp.

this is a screen grab of mine printing ABS - zoomed in to 10 minute time frame - note how straight that line is? that is what you want.

http://soliforum.com/i/?pnUbJe9.jpg

yes, there is a little fluctuation at the very beginning as it settles in, but after that it is dead flat, and it stays that way throughout the print

(and yes, the screen says "past 60 minutes" - it says that regardless of the zoom level =/ )

SD4 #1 & #2 - Lawsy carriages, E3D v6, Rumba controller board, mirror bed plate, X motor fan, upgraded PSU & Mica bed heater
SD4 #3 - in the works ~ Folgertech FT-5, rev 1
Printit Industries Beta Tester - Horizon H1

8 Reply by brucesdad13

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Re: Pololu DRV8825 for Extruder

I know so hard to diagnose. I've rebuilt and upgraded this printer for a month straight and still not quite there. Sometimes rather disheartening. wink My temp graph is straight across perfectly flat and even. I have an E3D V6 and 30A power supply so no real issue keeping the extruder at PLA temps. Hrm... I played with the belts tightening a bit the small Y belt and I also tried lowering the temp another 5C. I've switched over to printing a few Benchy boats. Sometimes it's two steps backwards because I had printed a squirrel, benchy, and dragon all at the same time and the came out looking very nice except that the nozzle must've snagged on some overextrusion or such and from a certain layer up they were all shifted in X. I tightened the X belt too. Now that I've been mucking around the prints aren't as nice. Pics coming once I have a decent print...

heartless wrote:

could be temperature, could be filament drag, could be a lot of things... it is so hard to diagnose over the internet. tongue

overall, the little guy looks pretty darn good, except for the couple of lines you already noted...

when printing, keep an eye on the temp graph - if you are getting a lot of fluctuation you may want to do a PID tune to stabilize the temp.

this is a screen grab of mine printing ABS - zoomed in to 10 minute time frame - note how straight that line is? that is what you want.

http://soliforum.com/i/?pnUbJe9.jpg

yes, there is a little fluctuation at the very beginning as it settles in, but after that it is dead flat, and it stays that way throughout the print

(and yes, the screen says "past 60 minutes" - it says that regardless of the zoom level =/ )

SD2 Pro + RH + Slic3r on Win7Ent (~Craigslist Oct. 2016 my 1st printer: upgrading & calibrating to near perfection)
- E3D V6 hotend; 30A PSU; Glass bed for ABS or Blue Tape on glass for PLA
- X-axis NEMA 14 press on fan (thing:1871741); Lawsy almost everything else; 3mm Z axis rod (thing:1868824)
- Sang board w/all headers, ATmega1284P w/OptiBoot and Marlin beta firmware; VRef tuned

brucesdad13's Website

9 Reply by carl_m1968

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Re: Pololu DRV8825 for Extruder

Have you tried printing at a . 1 or . 2 layer?  . 05 is really pushing it for some printers and could be beyond yours.  Every printer is different and just like filament even the same brand and model has variations. While one might be able to print that low another will not.  Honestly going below . 10 is overkill for even artistic prints.  The visible layers are a trademark of the technology. If you want to get rid of or minimize them then you will need a different technology like SLA or post finishing like cold vapor and fillers or sanding.

Printing since 2009 and still love it!
Anycubic 4MAX best $225 ever invested.
Voxelabs Proxima SLA. 6 inch 2k Mono LCD.
Anycubic Predator, massive Delta machine. 450 x 370 print envelope.

10 Reply by brucesdad13

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Re: Pololu DRV8825 for Extruder

That's good advice. I've switched to printing with more realistic layers and although things aren't perfect I'm happy that dimensionally I've had perfect fits. I've printed up a storm all week of Raspberry Pi 3 B and Arduino and breadboard holders. big_smile Among other items that help with electronics learning...

http://www.thingiverse.com/make:268906
http://www.thingiverse.com/make:268654
http://www.thingiverse.com/make:268905
http://www.thingiverse.com/make:268071
http://www.thingiverse.com/make:268907

SD2 Pro + RH + Slic3r on Win7Ent (~Craigslist Oct. 2016 my 1st printer: upgrading & calibrating to near perfection)
- E3D V6 hotend; 30A PSU; Glass bed for ABS or Blue Tape on glass for PLA
- X-axis NEMA 14 press on fan (thing:1871741); Lawsy almost everything else; 3mm Z axis rod (thing:1868824)
- Sang board w/all headers, ATmega1284P w/OptiBoot and Marlin beta firmware; VRef tuned

brucesdad13's Website