Installing and Configuring DRV8825 Stepper Drivers

I recently bought 2 of the new Silent Step Sticks which I wrote an instructable about: Install and configure SilentStepStick in RAMPS - TMC2100 Schrittmotortreiber - They really impressed me, and wanted to trade up my last two A4988 drivers for a pair of DRV8825 Sticks.

So, you might ask, why didn't I either just buy two more of the TMC2100 or keep the A4988 I had? Fair questions.

First answer is that the TMC2100 are rather expensive at 10 Euros or so a piece. At least it is expensive compared to it being a completely non-essential upgrade. I also weren't sure I would really get anything from my Z-axis. Not like it moves around a lot.

The Extruder on the other hand is moving A LOT, but I was afraid I had to crank up the power a lot on the TMC2100 and thus negate any positive effect on the noise I might have hoped for.

And here enters the DRV8825 Sticks. They go natively 1/32 at the same jumper settings the A4988 runs 1/16, which directly translates into a more silent running (potentially). They also have a heck of a lot of amperage headroom. More than I'm going to use on my small printer. Especially since I run a geared Extruder and have a very efficient Nema 17 motor that doesn't require much to put out a lot of torque.

I found two of these for 3 Euros, including freight on eBay. Even came with heatpads and fine heatsinks, which you want.

So, what I hope to achieve here is less noise and enough power to go by :)

0 - Intro

1. Index - Content
2. Preparing, Installing and configuring on RAMPS
   1. Not much to it, but the small steps are important
   2. Preparations
   3. Configuring Vref
3. Modifying the firmware and final Words
   1. Modifying firmware
   2. Further reading
   3. Linkks
   4. Final Words
   5. Update after a few days usage. - Verdict

Not much to it, but the small steps are important.
Preparations

Clean up the chip and heatsink with some Isopropyl-alcohol, attach the heatpad and heatsink. Carefull not to put sticky fingers on them.

I ran my old A4988 at 1/16 and I want to take advantage of the 1/32, so I'll just leave all three jumpers in place under each stepper.

Then install the new steppers with the potentiometer pointing the oppositve way of the A4988 (see images).

That means the driver is installed with the potentiometer close to the Ramps power plug.

Configuring Vref

In order to measure Vref you first need to turn on your printer as you normally would. If you only connecct using USB, but not external power, you get a wrong reading.

You need to turn on your multimeter and set it at 2v. Put the red one on the potentiometer and the Black one on the Gnd pin. Both are marked on the images here.

Before starting this I read they come with a very high vref setting, and it is recommended to start around 0.5v Vref. After measuring mine, I can confirm they come with a very high initial setting. Mine both came at 1,65v or so! - Yours might be different, which just underlines the importance of doing this.

Contrary to normal potentiometer usage, the ones on most copies/clones of DRV8825 are lowered by turning clock-wise, so that is what we will do, to we hit 0,5v on each. - A quarter of a full turn lowered it to 0,7v, - after that it goes very, very rapidly down, so aim for the quarter of a turn + a tiny tad more.
If you buy your DRV8825 directly from pololu.com the Potentiometer are dialed up by turning it clock-wise:

From Pololu regarding their driver: https://www.pololu.com/product/2133

The current limit on all of our stepper motor drivers increases as the potentiometer is turned clock-wise.

After fiddling alot I had mine around 0,6v and will give it a go before spending more time on this.

Modifying firmware

We also need to double the steps we have listed for the motors we just changed the Stepper Drivers on.

Fire up your Arduinio IDE, open the Marlin firmware and open the Configuration.h sketch*
* Each document is called a sketch, and is selected by clicking the different tabs.

Hit CTRL+F and write movement settings (be sure to have marked the "ignore case", or write with all capitals)

I'll recommend you save the original info on a new line with a preceeding double // to mark it as a comment. You can see I have comments on all my axes.

I assume you ran 1/16 on the affected axes, so you just simply need to double that number. Notice I kept comments on both the old and new one as I might want to change back at a later point, and because it is nice to know why my settings are as they are now.

I pointed out my resolution as well. As you can see it is very high, and I'm really never going to use that high resolution, but the noise should be lower, higher microstep-setting.

After you have entered the new values and written any comments you like, hit the Upload bottom (arrow pointing to the right).

I have seen some other guides which tells you to flip the wires, but that is really not needed. I do not know why they say that.

Further reading

If you want to read more on this subject, you can go here: http://reprap.org/wiki/Pololu_stepper_driver_boar...

Links to the original Pololu pages:
DRV8825 Stepper Motor Driver Carrier, High Current
Old version: md20a: https://www.pololu.com/product/2132
New version: md20b: https://www.pololu.com/product/2133

Final Words

My printer is now doing its first print, and I must say I can't really tell the difference. Both the Z-axis and the Extruder motor is doing a great job at the 0,6v vref.
One thing about the DRV8825 is that they are supposed to run way cooler. Seeing as I have DRV8825 and TMC2100 Stepper Drivers only now, I can safely remove my actively cooling solution.

Update after a few days usage. - Verdict

I must say I'm a bit disappointed really. At first I didn't think there was any difference, but I experienced some high pitched whine from the Z-stepper. It always went away when it changed to a new layer, but it was not pleasant. The Extruder however became really noisy. I'm using a geared bowden extruder which multiply the problem, as it runs back and forth a lot; especially when making small intricate objects!

I didn't measure the temperature, but the new 8825 didn't seem to be running particularily cooler. Neither did my Silent Step Sticks. I know they can handle a lot more heat than I can handle on my fingertips, but I had expected something else..

I ended up putting back in my old A4988s and put my fan back on :)

Update 4. august 2016

I have found the issues I'm facing comes down to incompatibility with the motors I'm using and the DRV8825.. semms they just do not like each other.
I have changed the extrudre motor and now the 8825 behaves really nice. I've also changed Z-motor and instead of almost constant layer-whine it only does it now and again...

What I'm trying to say here: it is potentionally a nice driver, but as it is now I'll stronly recommend buying TMC2100 or one of it's newer version than DRV8825.. or at least start buying 1-2 drivers to test if they match your machine.

I now run a combination of TMC2100 on X and Y. A4988 driver on Z and a DRV8825 on extruder. Am going to change the 4988 for a TMC2100 as well. I just didn't have an extra.