Stepper Motor Selection

Dear all,

I have doubt in the Stepper motor selection. May i know wich torque i have to use to select Stepper motor in the following list

1.Rated Torque
2.Peak Torque
3.Holding Torque

could you explain why?

Thanks & Regards

V.SIVA SHANKAR

Hey..

You are looking at Holding Torque, don't know why but you are looking for motor of about 70oz for the x, y and extruder, you can use lower rated ones for the z as they don't do much work..

Auzze

Isn't holding torque also the peak torque and the rated torque? I think they are all the same.

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[www.hydraraptor.blogspot.com]

re the various definitions: from the NEMA standard ICS 16

3.2.1.12.4 Rated Torque (Continuous torque, full load torque, output torque )
Torque developed at rated voltage and rated speed without exceeding the temperature rating.

3.2.1.12.3 Peak Torque
Maximum torque developed by a motor under specified conditions when teh maximum allowable peak current is applied.

3.2.3.20.4 Holding Torque
Peak resistance to rotation of a gradually rotated shaft of an energised motor for a specified mode of winding excitation and applied current.

but as the guys say above, for the purposes of a reprap it all simply comes down to the holding torque,
and for those of us metricificated - for (e.g.) a Prusa-Mendell, typical holding torque recommended is "at least 40 Newton*cm", NEMA 17 steppers.

Dear All,

Thanks for your reply

1. Can I get the smallest motor with 19Nm torque either servo or stepper motor. could you refer any manufacturers?
2. Can I go for direct drive motor instead of Servo & Stepper motor?
3. Could you explain if direct drive can perform same as Servo & Stepper motor?

Thanks & Regards

V.SIVA SHANKAR

nb99 Wrote:

> and for those of us metricificated - for (e.g.) a
> Prusa-Mendell, typical holding torque recommended
> is "at least 40 Newton*cm", NEMA 17 steppers.

Hm, interesting. Wiki page on stepper motors recommends using motors with approximately 13.7 N*cm. Where did you get 40 N*cm figure?

I'm particularly interested, because I'm currently selecting steppers for my first Prusa, and I'm seriously going to buy ones by Zapp Automation (I'm in the UK), which have holding torque of 21 N-cm. Now I'm confused, as if 40 N*cm recommendation is correct, those motors do not qualify.

Could anyone clarify the matter?

The 40 N*cm reference comes from the vitamins BOM on the Prusa page that you get to from the main reprap.org menu "Build a reprap" link.
[reprap.org]

It fits with the fact that the two makes of steppers I have seen advertised here in NZ for repraps are 48 N*cm.
However, I'm guessing its not an absolute limit - it's certainly worth getting other folks practical experiences as to whether the figure of 40 is over-conservative, and how low can you go....

My 48 Ncms have a ton of torque (so to speak) for all 4 Prusa axes, so presumably could get away with rather less before skipping happens.

added after some searching:
I see on the reprap.org/wiki/Stepper_motor page it does mention 13.7 N*cm - but I suspect that was in reference to the NEMA 14 steppers, the lists of motors on that page shows the small 14s with those lower torques, but most of the listed NEMA 17s are 40+.
Once again hearing from people what worked for them is probably most useful...

( random info: "14" and "17" refer to the width of the motor, 1.4in and 1.7in )

Edited 2 time(s). Last edit at 01/21/2012 07:12PM by nb99.

If your buying from Zapp I would recommend buying these. Nearly double the torque of the one you link at only £1 more.

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My Reprap blog

jds-reprap.blogspot.com

@nb99,

Thanks for pointing that out. I've updated the wiki page on stepper motors.

@JoeDaStudd,

That's what I've done. I missed them when I had first look.