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New Pololu-Style driver ST820

Posted by Yellobello 
New Pololu-Style driver ST820
December 22, 2018 05:06AM
Hi,
on some aliexpress stores a new Pololu-Style driver with ST´s ST820 chip has popped up.
It supports driving your motors with up to 45V which is kind of massive (would be cool for Nema23 in CNC use)
and supports REAL 1/256th microsteping which is IMHO the only Pololu-Style driver whith this feature.
not even the TMC2xxx drivers have real 256 microsteps, they take 16 Microsteps and interpolate them internally and
drive the Motors with 256 Microsteps.
To be honest 256 Microsteps is also kind of overkill and our Nema17s won´t be able to resolve them repeatably
but the feature is there, and I bet they will be as silent as the Trinamic drivers.
The driver is also quite cheap, 3.29$USD and keep in mind that the price will surely drop with time.
So, I think the chip will surely be a competitor to at least the TMC2208 since I bet it will be quite silent,
it does not support the back-EMF sensing StallGuard(TM) feature which the fancier Trinamics have
but then again, 3.29$ is quite cheap.

What do you guys think about the driver chips? Has anyone actually used one?

Aliexpress store link
Re: New Pololu-Style driver ST820
December 22, 2018 07:16AM
This is a pololu product that someone has cloned... [www.pololu.com]

It has very low current... see comparison table [www.pololu.com]
Re: New Pololu-Style driver ST820
December 22, 2018 08:56AM
The biggest problem with any of those modules is that they can't dissipate enough heat to let you run any but small motors at rated torque. Add an easily broken current setting pot (and who knows how much current you'll actually get when you twist it?) to it and you have a perfect recipe for an unrelaiable printer.

45V NEMA-23 motors? Sure, if they'll deliver any torque at the very low current that thermal dissipation allows in this module. Take a look at a DM860 driver module for CNC machines. See that heatsink? It's not there because it looks nice.

"real" 256:1 ustepping offers the "advantage" of requiring a 16x greater pulse rate to drive the motor at the same speed as a motor being driven at 16:1 ustepping (or using interpolated 256:1 ustepping). Calculate the maximum speed your controller can deliver at 16:1 ustepping and divide it by 16 if you use this module at 256:1. ooops.

At 256:1 this thing can't go fast enough for a 3D printer (OK, it would be fine in the Z axis) and it can't supply enough current for a CNC router or mill.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: New Pololu-Style driver ST820
December 22, 2018 12:48PM
Quote
Yellobello
...not even the TMC2xxx drivers have real 256 microsteps, they take 16 Microsteps and interpolate them internally and
drive the Motors with 256 Microsteps.

All the commonly-used Trinamic drivers can do genuine x256 microstepping - or any other binary microstepping between x1 and x256. But they also offer the ability to interpolate to x256 - in some models only from x16, in other models from any lower microstepping.

Edited 2 time(s). Last edit at 12/22/2018 12:51PM by dc42.



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: New Pololu-Style driver ST820
December 22, 2018 06:58PM
Quote
the_digital_dentist
At 256:1 this thing can't go fast enough for a 3D printer (OK, it would be fine in the Z axis) and it can't supply enough current for a CNC router or mill.

Off course this is nothing for the 8-bit electronics, but most 32-bit µCs have enough power to drive the high step rates required. We finally arrived in the 21st century
with marlin 2.0 supporting the new electronics… or take a look at Klipper.. Smoothieboard 2 pro even promises to have an FPGA for step pulse creation...and so on.


Quote
dc42
All the commonly-used Trinamic drivers can do genuine x256 microstepping - or any other binary microstepping between x1 and x256. But they also offer the ability to interpolate to x256 - in some models only from x16, in other models from any lower microstepping.

I just checked the datasheets and the TMC 2130 and the TMC2208 actually do have native 256 microsteps, I honestly didn´t know this. The TMC2100 does just the interpolation from
1/16th microstepping and was the first driver that was available in a pololu package. The newer chips actually do offer the native 1/256th microstepping only through their respective ways of configuring the chip digitally, but when doing it with the MSx pins they again only offer the interpolated 1/16th microstepping, which is what mislead me.
Ok, cool so the Trinamic drivers do actually have native 1/256th microstepping, I did not know this.

But to be honest the whole 1/256th microstepping thing is a bit over the top. As I already said, the motors can´t really reslove the half a million steps per revolution, the torque diminishes to almost nothing and when applied to 3D printing, even the differences from 1/16th to 1/32th microstepping in print quality are very hard to see, if at all. The motor noise however goes down a lot, but then again you can interpolate and have about the same results. Trinamic does this for a reason.

Also, I just looked at the pololu website and they have quite a few new drivers since I last checked, most noteably the ST820 and also the TB67S249­ driver which can deliver currents of 1.5A(4.5Apeak!) this is quite a lot, and it even can handle 47V... this now is really something very useable for CNC and Nema23s!
Re: New Pololu-Style driver ST820
December 23, 2018 11:01AM
Quote
Yellobello
...
But to be honest the whole 1/256th microstepping thing is a bit over the top. As I already said, the motors can´t really reslove the half a million steps per revolution, the torque diminishes to almost nothing and when applied to 3D printing, even the differences from 1/16th to 1/32th microstepping in print quality are very hard to see, if at all. The motor noise however goes down a lot, but then again you can interpolate and have about the same results. Trinamic does this for a reason.
...!

The point is indeed not to have a higher resolution but to come close to a pure sine wave leading to a smoother rotation, less vibration, therefore less noise. I guess it is also the reason the driver can do interpolation, no need for the controller to issue all the intermediate pulses.


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
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