Originally Posted by 109jb
Ah, ok so 1/2 microstepping is actually 400 pulses/rev settings on the drivers and Mach 3 motor tuning screen. 2 pulses per motor step. Correct?
So multiply the denominator and steps native to your stepper and get pulses per rev. So 1/8 microstepping would be set as (8 x 2000 =) 1600 pulse/rev.
So as microstepping in increased, likelihood of missed steps does as well? I read somewhere it increases torque too....I think I have some googling to do...
This is a topic for much debate. My understanding (and I have been corrected and or changed my beliefs a few times over the years with this hobby and most likely will again) is that microstepping is a tool for controlling resonance (the issue causing the roughness in your Y stepper). In actuality the stepper cant be between steps I dont think. I believe the resolution is determined by the leadscrews pitch and the number of steps of the selected stepper has (in this case 1.8deg/200steps per rev). I do understand a few areas within Mach to help with your issue and in explaining it to you it becomes clearer to me. Also when I am wrong, generally someone with a better understanding will set me straight. I have felt the frustration of silence also and would prefer input. I hope it is of use. There are issues with kernel speeds and potential of your computer to output enough pulses quickly at high step values is my understanding of why speeds can be limited. Still plenty to understand and read about. It is ongoing and there are many AHA moments.
I think I just had one of those AaaaHA moments......and I better reread this thread and re check my own settings too......thanks to all and thanks SwampDonkey for starting this....
Yes, micro-stepping most certainly DOES allow positioning between full steps. It would be useless otherwise.... But the exact size of those microsteps can vary considerably from the theoretical ideal. Doing 10X micro-stepping will NOT give you 10X the resolution.
And, in nearly all cases, the mechanical precision of the machine will be less than even the full-step resolution, due to backlash, flex, mechanical resonances, thermal expansion and countless other factors. So, if you're micro-stepping in an attempt to increase resolution or precision, you're just kidding yourself. It is primarily useful for mitigating mid-band resonance in stepper systems. Achieving even close to +/-0.001" accuracy is extremely difficult in the real world, and anyone who says otherwise doesn't know what he's talking about.
Regards,
Ray L.
Thanks Ray, I know that I have played with many different microstepping settiings only to find changes in speed but not accuracy necessarily. I get very confused on this topic and intentionally bring up what little I know hoping yours or someones correction will make it clear. I still wonder how the stepper could hold between poles with any predictablity. Of course there are many things I still wonder about this stuff. Like which class did I skip? Apparently all of the ones with this info LOL. Yesterday I saw you provide a formula on using a stepper for a power drawbar and the friction and involved. I am still trying to figure out how to word most of my questions. I always denied any reading or learning difficulties as a child, now at 50 maybe they were right. It is still fun though! Thanks.
The rotor simply reacts, fairly predictably, to the forces generated by the current in the coils. When you run current through one coil, the rotor snaps to a position that puts it in alignment with the magnetic field in that coil. Do the same for the other winding, and it snaps into alignment with that coil. It does this because the magnetic field creates a force that pulls on the rotor, exactly the way two magnets attract each other. Energize both coils at once, with equal current, and the rotor will snap to a position mid-way between the two coils. This is exactly what happend in half-step mode. Increase the current in one coil, and/or reduce current in the other, and the rotor is pulled closer to the coil with the higher current. That is precisely what micro-stepping does. A single coil is energized at full current ONLY when the motor is at a full-step position. If you're doing 10X micro-stepping, the next step will reduce the current on the first coil by roughly 10%, and energize the other coil at roughly 10% of its max current, pulling the rotor roughly 10% off the full-step position. The next step will reduce the first coil current another 10%, and increase the second coil current another 10%, and so on. It doesn't work quite so simply in the real world, due to frictional and other losses and non-linearities, but that is the basic concept.
Regards,
Ray L.
As Ray says guy's have a look here it's a pretty good animation
How Stepper Motors Work
Ray, Thanks for the explanation. I see MW has provided a link to a tutorial on steppers. I will have to watch it. I did believe I understood how the pole was attracted however I assumed all magnets were symetrically placed with 2 opposing magnets energized at the same time would create a central holding point. It never occurred to me about partially energizing one side and over energizing the opposite side. SD sorry to hijack your thread but loving the descriptions provided in helping my understanding.
MW, great link and description, Thanks
Glad to be of some tiny help
MW, Unfortunately I learn in "tiny" bits. The timing was perfect! ;-)
and you need a micrometer not a DTI to measure my "tiny" learning bits
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