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MKS LV8729 , a 128 µStep Driver // Any test?

Posted by epoxi 
Re: MKS LV8729 , a 128 µStep Driver // Any test?
March 25, 2018 05:40PM
Hey,

Just discovered this thread as am tempted to try LV8729's with my mks sbase 1.3. Did anyone have a chance to try 1/64 or 1/128 ? How is the noise then ? Or perhaps there's no use of that ? I think it's a misconception in my head that more microstepping is more quiet (probably isn't, right.. ?).

Thanks
Re: MKS LV8729 , a 128 µStep Driver // Any test?
March 26, 2018 03:20AM
I tried 1/64 and they were quiet, but they are quiet on 1/32 and I'm using an 8 bit controller so the number of steps/mm would be too high to achieve any reasonable speed at 1/64th.

More microstepping does mean less noise. That's why tmcs with 1/16th interpolated to 1/256th is both super quiet and very fast.

Edited 1 time(s). Last edit at 03/26/2018 03:21AM by DjDemonD.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
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Re: MKS LV8729 , a 128 µStep Driver // Any test?
April 23, 2018 05:16AM
I have noticed that some people have problems with their LV8729 drivers not having enough torque and I discovered something.
You can't use following formula for every LV8729 driver. Even if it is advertised on the sellers page because it just doesn't work for all of them. Chinese sellers like to copy paste info from others.
i = Vref / 0.5 (same as i = Vref * 2)


LV8729 datasheet gives us this formula instead:
i = ( Vref / 5 ) / RFI (2) resistance ( RFI is resistor and (2) means that there are 2 resistors.)



Yello LV8729 has two R100 ( 0.1Ω ) resistors, one on each side. This driver has default factory voltage ~0.4v. This means that you need to use following formula:
i = ( Vref / 5 ) / 0.1Ω ( Basically same as i = Vref / 0.5 or i = Vref * 2. )

For example:
( 0.4v / 5 ) / 0.1Ω = 0.8A
( 0.75v / 5 ) / 0.1Ω = 1.5A


And then there are two black LV8729 drivers. One of them has two R100 ( 0.1Ω ) resistors on the bottom which means you have to use the same formula as on the yellow driver.
But the other black driver has two R220 ( 0.22Ω ) resistors. And comes with default factory voltage ~0.8v. This means you have to use following formula:
i = ( Vref / 5 ) / 0.22Ω

For example:
( 0.4v / 5 ) / 0.22Ω = 0.36A
( 0.75v / 5 ) / 0.22Ω = 0.68A
( 0.8v / 5 ) / 0.22Ω = 0.73A
( 0.88v / 5 ) / 0.22Ω = 0.8A
( 1.0v / 5 ) / 0.22Ω = 0.91A
( 1.1v / 5 ) / 0.22Ω = 1.0A
( 1.43v / 5 ) / 0.22Ω = 1.3A
( 1.65v / 5 ) / 0.22Ω = 1.5A
( 1.98v / 5 ) / 0.22Ω = 1.8A
Re: MKS LV8729 , a 128 µStep Driver // Any test?
April 28, 2018 06:26PM
Just some additional info, since this is the first result when googling this driver: You may have to invert the enable pin signal if you are switching from A4988s, at least that's what I had to do to get them to work.

Concerning the drivers themselves:

They are much quieter than the A4988 but still quite audible when moving. Compared to the A4988 the sound is lower, being much easier on the ears. If no motor is moving they are practically completely silent. My A4988s produced a horrible headache-inducing whining sound when standing still, this is not a problem with the LV8729.

Since I have an ARM 32-bit-based board I can use 1/128 microstepping. The improvement compared to 1/32 is negligible though. The sound when moving is a bit lower and a little bit quieter, although not much so.
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