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New stepper drivers messing up print scale

Posted by GingerNinja 
New stepper drivers messing up print scale
December 19, 2018 08:01AM
Hey guys (and girls?)
I recently replaced the DRV A4988 stepper drivers on the x and y axes of my printer (sort of a prusa i3 running on ramps) with DRV8825 drivers. I put them the right way around and all, but now if I tell either of those axes to move say 50 mm, then it only moves 25 mm. I haven't changed any of the firmware settings . . .
I have all 3 jumpers under each driver so it should be running with 1/16 micro stepping right?
Do I need to change micro stepping or steps per unit settings?
Any help would be appreciated.

Thanks
Dan
Re: New stepper drivers messing up print scale
December 19, 2018 08:18AM
In the new marlin 1.1.9 they have a way to set the stepper drivers that are being used.

* Specify Stepper Driver types
* The options are used to determine driver pulse timings as well as more advanced functionality.
* Stepper timing options can be overridden in Configuration_adv.h
*
* Options: A4988, DRV8825, LV8729, L6470, TB6560, TB6600, TMC2100,
* TMC2130, TMC2130_STANDALONE, TMC2208, TMC2208_STANDALONE,
* TMC26X, TMC26X_STANDALONE, TMC2660, TMC2660_STANDALONE,
* TMC5130, TMC5130_STANDALONE


Computer Programmer / Electronics Technician
Re: New stepper drivers messing up print scale
December 19, 2018 09:55AM
The 8825 drivers are 1/32 steps with all 3 jumpers set
Re: New stepper drivers messing up print scale
December 19, 2018 10:21AM
Thanks Obewan
So in that case I double the steps per unit for the X and Y axes right? Or keep it as 1/16 and remove a jumper?
Re: New stepper drivers messing up print scale
December 19, 2018 10:25AM
If it moves fast enough, leave it at 32:1- the printer will probably run quieter than it will at 16:1.

Are you aware of the low speed step-skipping problem with the DRV8825s?


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: New stepper drivers messing up print scale
December 19, 2018 06:38PM
you need to either double your steps/mm or adjust the micro stepping jumpers following this table.

Micro stepping jumpers for DRV8825 (Jumper on == High)


Edited 1 time(s). Last edit at 12/19/2018 06:39PM by Dust.
Re: New stepper drivers messing up print scale
December 19, 2018 10:59PM
Thanks Dust smiling smiley

I tried doubling the steps per unit and was struggling to find a balance between the motors getting really hot (current too high?) and the motors losing synchronization when I decreased the voltage on the trim pot. Do the motors tend to run hotter at 1/32 micro stepping, or are the DRV8825 drivers just harder to tune than the A4988 ones?
Re: New stepper drivers messing up print scale
December 19, 2018 11:09PM
The DRV8825 uses a different formula to calculate Vref

I_TripMax = Vref × 2 
or 
Vref = I_TripMax / 2

Edited 1 time(s). Last edit at 12/19/2018 11:09PM by o_lampe.
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