[boydage]

Have just gone to 2510 screws instead of 1605 screws for the Y Gantry on my router. I am wondering what will be the best resolution for the Nema 24s I have they are closed loop.

I think if I remember they are currently at 1600 SPR and am thinking that setting them too 2000 SPR might be the best way to go??? More or less? Setting I think is correct at 200 steps per mm for a 10mm pitch screw.

What do you guys think or have done if you have used 2010s?

[peteeng]

Hello Boydage - Resolution of a stepper motor is a two part issue 1) mechanical resolution or tolerance and b) electronic resolution or tolerance. If you have a standard 200 steps per rev motor with a +/-5% tolerance this means the following: (You can get 2% tolerance steppers and I have used 400 step motors with 5% tolerance so they are twice as accurate as a std one)

1 step is 360/200=1.8deg that 1.8deg is +/-0.05*1.8 = +/-0.090degs

Now you have the microsteps to consider - 1) microstepping is not a "hard" step it is a soft step and can vary quite a bit. But it gets reset every mechanical step +/- the tolerance of the step. 2) so with a 10mm lead screw 10mm = 1 rev = 200 mechanical steps. 10/200= 0.050mm per step at that point , 0.050mm +/-0.0025mm. So you can't achieve any better then +/-0.0025mm due to the mechanical reset....

So now look at the 1600usteps per rev. This is 10/1600= 0.0063mm and 2000usteps is 0.005mm and 4000usteps is 0.0025mm but remember these are not "accurate" steps they depend on the torque applied to the motor, the velocity etc etc.... If your drivers are good more usteps means smoother running so 4000 maybe good but no point going past 4000 as this is the mechanical accuracy... then there is to top freq of the driver to consider with the speeds you want to go... Many systems run 1200 or 2000 as the top number as past that there is no physical advantage. . Cheers Peter

[boydage]

Thanks Peter. Appreciate that. I didn't know some of what you wrote so yeh, thanks.

I am pushing quite a lot of mass with these little Nema 24s. I got them going today. They are closed loop, moving a large amount of mass with new seals. Certainly no problem with torque but the two motors sounded like they were bumping (electrically). Kind of as if one might be very slightly ahead causing the second one to catchup with a zip sound. Know what I mean with that explanation? It was intermittent too and one direction is better than the other.

Anyway. I ended up setting them at 1000 and they ran best that way. Also the encoders are 1000 line so I wonder if that also adds to a smoother run.

I am going to finish the installation off. Its a major modification. If the Nema 24s don't perform well I guess it's upgrade to something larger. Gee. That's going to be a few dollars. Regards Boyd

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