How to change your A4988 stepper driver by DRV8825 ones

[phervier]

There is two main reason to change them :

• the DRV8825 is more efficient, it may deliver a 1.5A constant current to the motor without the need of active cooling
  
• it offers 1/32 microsteps vs 1/16 for the A4988 allowing more precision in the positioning. But keep in mind that smaller microsteps means less torque and more CPU needed for computation. As the delta printer are already very demanding in cpu power, it may speed down the printings.
  

First mounting same precision 1/16 step :

The example pictures are for the X axis driver it is the same thing for all the drivers.

• Remove the A4988, and remove the ms1 and ms2 jumpers (see photo).
  
  
• Put the DRV8825 in place, the IC is on the opposite side of the board compared to A4988.
  
• switch the power on (the motors should be connected) and set the appropriate voltage.
  In my case I have 42SHD0217-24B stepper motors, it is writen on the back of motors but not really readable. On the Geeetech site they are given for 1.5 of nominal amperage so the reference tension should be 0.75V
  you should measure the voltage on the side of the potentiometer (see picture), It is quite difficult to have a precise reference voltage as the overall range is very large.

it is done ! you may now use your motor at full power without too many heating.

Second mounting 1/32 step :

• Replace the A4988 by the DRV8825 without changing jumpers
  
• set up reference voltage (see higher)
  
• In your firmware change the number of steps by unit. In marlin it is the DEFAULT_AXIS_STEPS_PER_UNIT array constant, in configuration.h file. You should double values for the axes you change (in this order X Y Z Extruders). Update your firmware.
  switch on the printer connect it on your computer and send the following commands :
  
      M502 ; to take into account new constant values
      M500 ; to save the values in the EEPROM

It is done !

[piscanc]

nice writeup.

Few questions

Do 8825 drivers also come with different sense resistors like A4988? I have inbound ones from geeetech and i see your got R100 ones on.

Do you use them as 1/16 or 1/32, regarding speed?
Is 1/32 capable of printing at 100mm/s?

Marko

[phervier]

As far as i know there is only one flavor of DRV8825 but we may rely on Chinese copyist inventiveness to make new ones.

I bought mine from Geeetech, but only 4 (I do not remember why) so I could change only X Y Z axis at the moment. I used them at 1/32 steps without any problems. I am waiting a 5th one from another supplier.

I tried to print at 100mm/s the infill, moves seem ok but the extruders motor blocked sometimes. As it is still with bad A4988 at 35% of their nominal power I think the DRV8825 may allow this speed. I think i will use them at 1/16 steps on extruders to have more torque.

[wilsoc5]

Great guide. I just did this upgrade (1/32 stepping and voltage set at 0.72) and now for some reason my motors won't stop when homing. M119 correctly registers the switches whenever I do it manually. Still using Marlin and tried your github version of marlin with same problem. Thoughts? I can manually move the motors after a restart (and then hitting one of the switches manually), and each switch works correctly. Just not in homing.

[wilsoc5]

Nevermind. Apparently my X and Y towers got crossed when I reassembled it.

[uzi3l]

great write up. I'm waiting on 5 for my printer. one question and sorry if this is stupid where have did you ground you multimeter?
on the A4988 i did it to the GND on its self, (gets very fiddly) but i see you have just the +(red) touching the potentiometer.

[spikey1973]

@ phervier: great work-up..

just one question.. i understand the part of measuring the voltage on the side of the potentio meter.. but where do you connect to ground?
really difficult to see on the picture and i really don't know what would be a good point for this.

greatz matthieu

never mind... found one. i'll try to explain where for the once after me that have the same issue.
since i don't have a picture online i can't post it here so i'll try to navigate through it with the use of the layout image of the gt2560 board from geeetech. 

on the image there is a bare metal contact point of 8x5 mm inbetween the dipswitches / jumpers of the extruder 2 stepper driver and the bluish part with 150 printed on it (inductor). on my board there was a component mounted (forgot how they are called) on there.. if this is the case. no problem, it is soldered with two / three legs (can't remember) at the bottom and a straight bar at the top. use this straight bar, it is a ground. 

i set them all 5 on 7.49 V (strangely enough it was nearly impossible to get them on to 7.5, but easy enough to get them all the same so i set the to the value nearest to 7.5, being 7.49)

[wavey75]

Thanks for this guide, it's great.

I'm confused by a couple of things, so I just wanted to clear them up. When you say 1st mounting & 2nd mounting, does this mean I can either do it this way OR do it the other way, or MUST I do both things to use these newer driver chips?

Also, is checking the voltage just for peace of mind, or should we record the reading and enter it into the firmware somewhere?

Sorry if my questions sound a little like I'm nit-picking, but I'm confused and my drvier chips and stepper motors are getting very, very hotand I'm trying to fix the problem.