Stepper Motor Selection

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Stepper Motor Selection

Post by rstuckey » Tue Jun 12, 2018 5:05 am

I have a k-flop, and kanalog. Will go Servo route eventually, but considering Kstep with steppers just to get my small milling machine going.
If I were to max out the performance of the Kstep, can anyone suggest what sort of specifications I should be looking for in my stepper motor selection?

Thinking of stepper that has:

2 phase
0.42 ohm per winding
Model: JMC , 86J1895EC-1000

What are your brief thoughts?

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Re: Stepper Motor Selection

Post by TomKerekes » Tue Jun 12, 2018 6:14 pm

Here are some thoughts:

The inductance of 4.1mH will probably limit the speed significantly to several hundred RPM.

KStep's limit of 5A shouldn't reduce performance much.

The low resistance and low motor voltage will limit the supply voltage that can be used with KSTEP. To have good microstepping with KStep the Supply voltage must be < 12X the motor voltage. Or:

5A x 0.42 Ohms x 12 = 25V

Ironically relatively long thin motor cables can add resistance and help in this regard.

Tom Kerekes
Dynomotion, Inc.

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Re: Stepper Motor Selection

Post by Moray » Tue Jun 12, 2018 9:40 pm

Motor inductance is the main contributing factor to a stepper motors performance, as the higher the inductance, the higher a voltage that's needed to force the current through the coils at speed. So if you have limited voltage, then you want motors with as low an inductance as possible.

You'll often get better performance with a smaller motor spinning faster via gearing, than a big motor spinning slower with no gearing.

It's worth have a read of Gecko Drive's stepper motor basics, as it has a reasonable amount of info without being too technical - ... asics.html

If you were in the UK, my recommendation would be the NEMA23 motors from cnc4you. They do 3.1Nm motors with an inductance of 3.2mH, and 2.2Nm with 2.5mH ( ... 01B-Nema23 and respectively). Or they also have a 4Nm with an inductance of 3.0mH.
Using the gecko drive voltage recommendation calc of 32 x square root(inductance), means the 2.2Nm ideally needs 47V, the 3.1Nm 57V, and the 4Nm 55V.

I'm sure if you look at the relevant datasheets, and search for the motor model numbers, you'll find similar motors from a more local supplier. You may even find performance graphs for the motors, which will give a good idea how they'll act at speed. However, as you say it's for a small mill, I'm going to guess you won't be needing them to spin them that fast.

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Re: Stepper Motor Selection

Post by rstuckey » Wed Jun 13, 2018 11:06 am

Thank you very much for the extensive responses to my questions.
It appears that there is a lot more to selecting the correct motor than I had originally thought.
It would appear from a cursory look at discussions about stepper selection that inductance isn't discussed as often as it should be.
I'll let you all know how I go.

On another note, I am really looking forward to getting involved with this discussion group.

Kind Regards
Richard Stuckey.

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