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Soldering resistor onto A4988's ROSC pin

Posted by Ohmarinus 
Soldering resistor onto A4988's ROSC pin
February 04, 2015 12:51PM
Hi guys, I want to try and lower the vibration on my cheap stepper drivers, on my other printer I have these drivers: [reprap.org] and they work really well. But I think it can be simply done by just adding a resistor over two pins.

I have a few spare stepper drivers laying around so am willing to try some experimentation.

Can anyone explain to me which stepper pins I have to connect with what kind of resistor? I have read about someone who has done this before, and have been using the search, but it's been two years ago and can't seem to find it back anymore.

There is some talk about this on this page, but I haven't found the exact info I'm looking for:
[hydraraptor.blogspot.nl]


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 01:57PM
+1 for finding the answer. I would love to see how this is done. This could be very useful if it's effective and easy to implement.
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 02:02PM
Quote
jtoombs
+1 for finding the answer. I would love to see how this is done. This could be very useful if it's effective and easy to implement.

Yeah, I could just buy another set of Gadget3D's drivers, but I'd rather learn how to do this myself. My other printer is virtually silent, the fans make more sound than the motors! My new printer is a CoreXY, just like yours, and has a very stiff frame. I hope to be able to improve (lower) the vibration myself.


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 02:11PM
Wooo! Found it smiling smiley

You short the R4 resistor on A4988 stepper drivers... The fix is described >>HERE<< (but in GERMAN)


-David

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Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 02:41PM
Quote
MindRealm
Wooo! Found it smiling smiley

You short the R4 resistor on A4988 stepper drivers... The fix is described >>HERE<< (but in GERMAN)

Simply shorting it? But, R4 to what pin? Ground? I don't have to put a resistor from R4 to ground, but simply short R4 to ground? This sounds easier than I thought!

From translating it I found:
"so I have the R4 10k resistor bridges"

So this probably means I have to pull R4 to ground with a 10K resistor?


There is another German topic about this:
[translate.googleusercontent.com]

Edited 2 time(s). Last edit at 02/04/2015 02:47PM by Ohmarinus.


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 04:03PM
Download the A4988 datasheet and work it out from that. I'd do that for you, but it's not very practical on a mobile.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 04:13PM
Quote
dc42
Download the A4988 datasheet and work it out from that. I'd do that for you, but it's not very practical on a mobile.

I'm not easily insulted, so I'm not, but really, I did that already and I'm not so good at that. Hence me asking help from the community winking smiley

The file is here:
[www.pololu.com]

PDF:
[www.pololu.com]


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 04:26PM
If you don't get a definitive answer by tomorrow morning, I will have access to a computer then, so feel free to remind me about this thread by PM.



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

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 04:46PM
Quote
Ohmarinus
From translating it I found:
"so I have the R4 10k resistor bridges"

So this probably means I have to pull R4 to ground with a 10K resistor?
I think it means the R4 is a 10K resistor and he is "bridging" it....meaning shorting it out.

That would put the ROSC pin at ground (note that the R2 that would be the top of the divider for ROSC is NP....not populated).

At least that's my guess for this "mod" as I have no idea what the ROSC pin on the driver IC is for.
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 06:22PM
Thanks, it's interesting that they tell what they did, but don't show a picture of the physical change they made to the stepper driver..

Judging from this somewhat unclear image, it looks like you only have to bridge the resistor:


Title of the image is:
Quote

On the Pololu A4988 boards a small resistance has to be bridged, here done with a small piece of wire:
[Attachment 37445 hack_pololu.jpg]
(Picture by hardware Killer)

Edited 1 time(s). Last edit at 02/04/2015 06:37PM by Ohmarinus.


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 07:15PM
Ohmarinus,
You are right, you only have to bridge the resistor.
On a surface mount resistor the two ends have caps that are solderable.

One side of the resistor is connected to ground, soldering a wire across it does the trick and switches to "mixed decay" 100% of the time.

The docs indicate this can help not miss microsteps when stepping slowly.

I don't know if it makes them quieter. Higher micro stepping can help. Driving them smoothly can help, my Smootieboard is much quieter than my Rumba (different drivers),


My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
Can you answer questions about Calibration, Printing issues, Mechanics? Write it up and improve the Wiki!
Re: Soldering resistor onto A4988's ROSC pin
February 04, 2015 07:33PM
I will try this tomorrow. The drivers that I have, has the resistor placed on a slightly different place so I have to remove the cooling elements in order to solder the wires in place. Maybe I even have to buy a new soldering tip, my current tip is too big for soldering SMC-size things.

Will update on this when I manage to fix (might be tomorrow evening).


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
February 05, 2015 01:44PM
First experiments sound very promising, will upload a side-by-side comparison video later today smiling smiley Vibration is down by a lot and noise production by a bit smiling smiley

Oh, and it's superhard to solder an SMD that isn't stuck to the PCB! So I simply removed them and pulled a solder trace to short out R4.

Edited 1 time(s). Last edit at 02/05/2015 01:54PM by Ohmarinus.


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
February 05, 2015 04:00PM
I was actually really skeptical of this modification. Why would grounding a pin reduce vibration, and if its so helpful why not make it default behavior?

It turns out that this mod is for real, and confirmed in the datasheet.



Note that in a 3d printer the stepper motor is almost exclusively low speed, especially in pulley systems that have low mechanical reduction.

The default behavior switches decay modes and is more efficient, but has discontinuities at the transition. At low speeds this is reflected by a "jump" which is likely what causes your vibration.
Re: Soldering resistor onto A4988's ROSC pin
February 05, 2015 06:01PM
Quote
Ohmarinus
First experiments sound very promising, will upload a side-by-side comparison video later today smiling smiley Vibration is down by a lot and noise production by a bit smiling smiley

Oh, and it's superhard to solder an SMD that isn't stuck to the PCB! So I simply removed them and pulled a solder trace to short out R4.

Maybe this mod makes it possible to screw down the current a bit, because it says there is less chance in skipping steps. That would decrease the sound level even more.
Re: Soldering resistor onto A4988's ROSC pin
February 05, 2015 08:00PM
I can try that. Actually, I can run the steppers now even without a heat sink... So probably it can even do with less power.


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
February 05, 2015 11:33PM
Ohmarinus, what is the coil resistance in your stepper motors? I read in the comments on the page Nophead wrote about this mod that this only works with low resistance motors. His were 1.65 ohms. Do you have low resistance coils?
Re: Soldering resistor onto A4988's ROSC pin
February 06, 2015 07:51AM
Phase Resistance: 1.7 Ohm ± 10% (20º C)

So in theory, that should be close to 1.65 Ohms.

Oh, and they're 1.2A stepper motors. Properly running, not getting hot. I think CoreXY needs way less power to move the carriage, since the movements are always coordinated by two motors simultaneously.

Edited 1 time(s). Last edit at 02/06/2015 07:53AM by Ohmarinus.


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
October 31, 2016 05:58AM
can someone post a pic of the modification?

R4 (0 Ohms) has to be removed ?

thanks!
Re: Soldering resistor onto A4988's ROSC pin
October 31, 2016 07:49AM
If your R4 is marked 0 ohms then your driver is allready modified, the old drivers used to have a R4=10kohms which needed to be shorted out.
Re: Soldering resistor onto A4988's ROSC pin
October 31, 2016 09:31AM
Quote
obewan
If your R4 is marked 0 ohms then your driver is allready modified, the old drivers used to have a R4=10kohms which needed to be shorted out.

this means my drivers are already into mixed decay mode?
Re: Soldering resistor onto A4988's ROSC pin
October 31, 2016 11:43AM
Confusing because I think that bridging and shorting are two different things. Are they?
Re: Soldering resistor onto A4988's ROSC pin
October 31, 2016 12:01PM
Quote
KDog
Confusing because I think that bridging and shorting are two different things. Are they?

nope, same thing,
Re: Soldering resistor onto A4988's ROSC pin
April 22, 2019 09:32AM
I was looking for an old thread I swore I had read somewhere in the past about shorting a pin on the A4988. I had not expected it was my own thread from more than four years ago.

Anyway, wanted to let you know that even after all this time, the CoreXY-lasercutter still runs perfectly silent. It's such a nice mod, that I've also done this mod to my other 3D-printers smiling smiley

Recently, my 3D-printer that I currently had working, has died with electrical issues and I have replaced the stepper drivers for cheap old A4988's, these ones I still have to short so I can record a before and after if anyone is interested? I know that the reprap printers are at the brink of disappearance, the forums have gone very quiet and everyone around me simply buys Chinese ready-made printers. No need for DIY anymore it seems. Even though I think DIY is still the best way to learn anything about these machines so I'll just wholeheartedly keep doing this.


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
April 22, 2019 01:30PM
I'd love to see(hear) the before and after
Re: Soldering resistor onto A4988's ROSC pin
April 22, 2019 06:04PM
Most of my printers have A4988 drivers. I now _have_ to try this mod to see if it takes the noise and jitter down a bit!

DLC


Kits: He3D K200 Kossel, Folgertech Kossel 2020 upgraded E3Dv6, Anet A8 upgraded E3Dv6, Tevo Tarantula enhanced parts and dual-head
Scratch: Large bed Cartesian, Linear slide Delta, Maker-Beam XL Micro Delta
Re: Soldering resistor onto A4988's ROSC pin
April 23, 2019 01:24AM
I'll be looking over the v0.6 duet schematics to see what their default setting is!
Re: Soldering resistor onto A4988's ROSC pin
April 24, 2019 04:31AM
Quote
obelisk79
I'd love to see(hear) the before and after

Okay, so I have made a video with before and after. Sadly somehow my video editing software cannot use the video files from my phone (Pocophone F1) so I have uploaded two videos with before and afters.

Before (part 1):
[youtu.be]

After (part 2):
[youtu.be]

In video #2 I show the specific mod at the end.

I hope it's clear smiling smiley any comments are welcome as I'd like to hear your reactions.

Edited 1 time(s). Last edit at 04/24/2019 04:47AM by Ohmarinus.


http://www.marinusdebeer.nl/
Re: Soldering resistor onto A4988's ROSC pin
April 24, 2019 04:47AM
@Ohmarinus

ffmpeg can convert nearly all video and audio formats, and it free

Seems only slightly quieter... and that could be due to different recording devices...
Re: Soldering resistor onto A4988's ROSC pin
April 24, 2019 04:48AM
Quote
Dust
@Ohmarinus

ffmpeg can convert nearly all video and audio formats, and it free

Seems only slightly quieter... and that could be due to different recording devices...

It's recorded on the same phone smiling smiley I think it's a big difference. Maybe it's the playback device you're using? j/k.


http://www.marinusdebeer.nl/
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