Stepper Motor microstepping

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

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?

Hi John.

As an example a DM 556

DM556 stepper driver

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,

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%.

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

My mistake I have A and B mixed

Edited By Martin Kyte on 01/01/2023 10:48:36

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! )

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.

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.

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

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.

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

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!

John's right...

My first mistake of the new year. I'm on track to make sackcloth and ashes fashionable!