Stepper Motor microstepping

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Stepper Motor microstepping

This topic has 16 replies, 5 voices, and was last updated 1 January 2023 at 17:10 by ianj.

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31 December 2022 at 22:34 #626961
ianj
Participant
@ians
Looking at various stepper motor drivers, the dip switch settings on some for micro stepping have 1 (200 steps), 2A (400 steps) , 2B (400 steps) etc Can some one tell me what the difference is between 2A and 2B micro steps.

Ian
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31 December 2022 at 22:34 #15405
ianj
Participant
@ians
2A and 2B microstepping
31 December 2022 at 23:37 #626963
John Haine
Participant
@johnhaine32865
Hi Ian, I have never seen this on the drivers I have used (admittedly a small sample of 5 types). Could you provide more details on what type you are looking at please?
31 December 2022 at 23:50 #626964
ianj
Participant
@ians
Hi John.

As an example a DM 556

DM556 stepper driver
1 January 2023 at 09:55 #626984
Andy_G
Participant
@andy_g
The difference is in the waveforms used – have a look a pages 18 and 19 of the TBA 6600 chip datasheet:

**LINK**

I can’t see that there would be much practical difference, but one mode may reduce motor noise or be less vulnerable to resonance problems than the other in a specific application,
1 January 2023 at 10:37 #626994
John Haine
Participant
@johnhaine32865
Thanks Andy. Looking at those diagrams (b) looks like the "old fashioned" type where the coil currents are 0 or +/- 100% whereas (a) reflects more "modern" practice where at the intermediate stage the currents are 1/root(2) of max (70.71%).

I would suggest using (a) as a default, will probably give smoother operation. Mode (b) is probably to use the driver in legacy systems that might have used the old L297/298 style chips. Mind you the TB6600 is not a modern driver chip either, and I have read it has a reputation for blowing easily. Modern stepper driver chips like the A4988 (not so modern), and the TI DRV8825 and 8834 don't seem to have the alternate modes and only support the 70.71%.
1 January 2023 at 10:42 #626999
Martin Kyte
Participant
@martinkyte99762
I would agree with Andy, excitation mode B should produce more torque at low speed and mode Ashould run more smoothly at higher speeds. Mode 1 is probably better positionally. I would tend to select on test but with that in mind.

regards Martin

Edited to get the A and B the right way round.

Edited By Martin Kyte on 01/01/2023 10:50:51
1 January 2023 at 10:45 #627001
Martin Kyte
Participant
@martinkyte99762
My mistake I have A and B mixed

Edited By Martin Kyte on 01/01/2023 10:48:36
1 January 2023 at 10:53 #627004
Andy_G
Participant
@andy_g
Posted by ian j on 31/12/2022 23:50:30:

Hi John.

As an example a DM 556

DM556 stepper driver

As an aside, I'm pretty sure that isn't a genuine DM556 driver – it looks just like all the ones badged as TB6600, etc.

The real DM 556 doesn't have the 2A/2B modes and goes up to 128 microsteps –

DM556 driver manual

'Generic' TB6600 etc example

I believe that the *real* TB6600 chip (42V / 4.5A) only goes to 16 microsteps – these all go to 32, and are therefore "fakes" based on some other chip. Like John, I have heard of problems with these, where the rating of the actual chip used is less than the sticker on the case.

Interesting article here:

I only found out about this *after* I bought some (very cheaply!). Touch wood, they have been performing OK on my little CNC at 36V and ~3A.

(A happy New Year to all, btw! )
1 January 2023 at 11:03 #627007
John Haine
Participant
@johnhaine32865
Posted by Martin Kyte on 01/01/2023 10:42:09:

I would agree with Andy, excitation mode B should produce more torque at low speed and mode Ashould run more smoothly at higher speeds. Mode 1 is probably better positionally. I would tend to select on test but with that in mind.

regards Martin

Edited to get the A and B the right way round.

Edited By Martin Kyte on 01/01/2023 10:50:51

Hmm, I'm not sure. Mode B will produce more torque at the intermediate steps than the full step whereas with A which is true microstepping the torque should be equal. I normally find anyway that it's best to use at least x4 microstepping for smooth operation. Interesting that modern drivers seem to have abandoned mode A.
1 January 2023 at 11:19 #627013
Martin Kyte
Participant
@martinkyte99762
I agree with you John I don’t mean more torque than full stepping but compared to the other half stepping mode. Modern drives switch between micro stepping at slow speeds and full stepping at higher speeds which combines the advantages of both.
1 January 2023 at 11:43 #627020
SillyOldDuffer
Moderator
@sillyoldduffer
Posted by John Haine on 01/01/2023 11:03:40:

Posted by Martin Kyte on 01/01/2023 10:42:09:

I would agree with Andy, excitation mode B should produce more torque at low speed and mode Ashould run more smoothly at higher speeds. Mode 1 is probably better positionally. I would tend to select on test but with that in mind.

regards Martin

Edited to get the A and B the right way round.

Edited By Martin Kyte on 01/01/2023 10:50:51

Hmm, I'm not sure. Mode B will produce more torque at the intermediate steps than the full step whereas with A which is true microstepping the torque should be equal. I normally find anyway that it's best to use at least x4 microstepping for smooth operation. Interesting that modern drivers seem to have abandoned mode A.

My understanding:

Mode A produces a simple ON/OFF wave, which uses less power than Mode B, but inferior torque, acceleration, and more resonance effects. It's appropriate when the motor drives a fixed load at constant speed, which I guess is an unusual way of using a stepper motor.

Mode B ramps the wave from ON to OFF and back with one or more extra steps. Mode B consumes more power, but improves torque and acceleration whilst reducing resonant vibrations.

For many ordinary purposes, the difference may not matter, but I always select Mode B.

Dave
1 January 2023 at 11:52 #627022
Andy_G
Participant
@andy_g
Posted by John Haine on 01/01/2023 10:37:57:

Mode (b) is probably to use the driver in legacy systems

I agree – I'm pretty sure it's to mimic the old 'half stepping' drives that were in use before PWM became common.

In any case, a genuine DM556 would not have this setting.
1 January 2023 at 13:15 #627033
ianj
Participant
@ians
Thanks to all for your replies. All very interesting and useful information. I think I will use mode B, it's to drive a 4" rotary table and the extra torque will be good.

Happy New Year.

Ian
1 January 2023 at 13:46 #627039
John Haine
Participant
@johnhaine32865
Ian, I would suggest that you actually try both modes and Mode A may give better performance. And you may be better off using a higher microstep ratio anyway, depending on how fast you want to run.

Dave, according to the TB6600 datasheet it's the other way round!
1 January 2023 at 16:58 #627073
SillyOldDuffer
Moderator
@sillyoldduffer
Posted by John Haine on 01/01/2023 13:46:26:

…

Dave, according to the TB6600 datasheet it's the other way round!

John's right…

My first mistake of the new year. I'm on track to make sackcloth and ashes fashionable!
1 January 2023 at 17:10 #627079
ianj
Participant
@ians
Posted by John Haine on 01/01/2023 13:46:26:

Ian, I would suggest that you actually try both modes and Mode A may give better performance. And you may be better off using a higher microstep ratio anyway, depending on how fast you want to run.

ok John Mode A it is.
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