Help with final motor specification decision

Hello

It would be really nice if I could get your opinion for a stepper motor buying decision. It is for a 4 motor 3 axis CNC machine for wood machining, featuring a 2.2kW air cooled spindle.

The setup is:
– 2005 ball screws with 12mm machined end for joint coupling
– 8mm/12mm round or 14mm/12mm keyed plum flower type shaft coupler (depending on choice below)
– 20mm linear rails

The drives are 4 x DM556T (made by Leadshine), featuring the following current table choices:
Peak RMS
– 3.8A 2.7A
– 4.3A 3.1A
– 4.9A 3.5A
– 5.6A 4.0A

The choice is between:

1) NEMA23
Current / phase 4.2A
Resistance 0.9 ohm
Rated Voltage 3.78V
Inductance 3.8mH
Holding Torque 3Nm
Phase / Wires 2 / 4
Shaft 8mm

2) NEMA34
Current / phase 4.0A
Resistance 0.31 ohm
Rated Voltage 1.36V
Inductance 2.86mH
Holding Torque 4.5Nm
Phase / Wires 2 / 4
Shaft 14mm

Price is not an issue here, as both solutions are virtually identical in price.

I saw a number of posts online that recommend NEMA 23 over NEMA 34 based on smaller motors having a larger torque at higher RPMs – as required by the 5mm ball screw. However what attracted my attention to this NEMA 34 motor was the very low inductance (even compared to the NEMA 23) while also providing a higher holding torque. Unfortunately I don't have any torque diagrams available.

Further, the NEMA 23 has a 8mm shaft, whereas the NEMA 34 has a 14mm one. The 20mm ball screw is 12mm diameter with respect to the coupling connection. Would you be concerned going from 8mm to 14mm with the coupler?

Could you please let me know your opinions?

Thanks,
Christian

None of them.
For one, with your drives limited to 50v max nema34 are out of it.
For second, 3.8mh inductance is too high.

https://www.omc-stepperonline.com/ne...m-4-wires.html

A motor like this would be much better, with the drive set to 5.6amps.
https://www.automationtechnologiesin...-single-shaft/

Hello

Thank you both for your replies and recommendations. Both are really great suggestion of motors with very low inductance. I am particularly interested now in the StepperOnline motor.

Dsap1976 – Could I ask you please about your setup. I saw you posting in another thread where you mentioned going from 7Nm NEMA 34 to 4Nm NEMA 24 while running at 60V. The motor you pointed me to has 1.85mH. The formula I was taught to use to calculate V(max) is 32 x SQRT( Inductance in mH ), which would result in 44V max supply voltage. Are you running a similar low inductance motor at 60V despite that? I am trying to understand if I am making a mistake with the voltage calculation.

Thanks,
Christian

Hi,
the simple rule is use the highest voltage drivers and power supply you can get your hands on. The higher the voltage
the faster you can go before the inevitable degradation of torque defeats yor stepper.

Craig

Hello

Yes, sure. But there is a recommended maximum for each motor, right? The above formula seems to be the general recommendation on the internet, but for very low inductance motors this also would results in a lower recommended maximum supply voltage value.

I was curious how far anybody here is actually pushing it. So if you are running a very low induction motor at a high supply voltage it would be interesting to know. Are people using different formulas to calculate the recommended maximum?

Thanks,
Christian

Hi,

Quote:

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But there is a recommended maximum for each motor, right?

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No. Have you ever seen on any of the stepper spec sheets a maximum recommended driver voltage? At most they list the insulation voltage withstand, usually 500V.

Quote:

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but for very low inductance motors this also would results in a lower recommended maximum supply voltage value.

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No, the whole point about getting the lowest inductance motor you can is to go as fast as you can without undue degradation of torque. Don't throw it all away
by using a lower driver voltage, use the maximum you can find.

I drive my Vexta steppers with genuine Vexta drivers. The drivers are powered direct off the 230VAC line but internal to each driver is a DC power supply of about 150VDC.
Thus the drivers are supplying to the stepper 150VDC pulses......they go like hell. I routinely run them at 2400rpm but have run them at 3000rpm without losing steps.

Craig

Quote:

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But there is a recommended maximum for each motor, right?

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Gecko came out with that formula, and they claim that higher voltages don't offer any benefit.
Lots of users have found that higher voltages do indeed run faster, and modern high end drives keep the motors cool at those higher voltages.
The only real limit is to keep the motors from getting too hot. (<80°C)

Thanks Gerry - now that you mention it, I am sure that the Gecko documentation is exactly where I had my information from.

Christian

Quote:

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The only real limit is to keep the motors from getting too hot. (<80°C)

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I used nema 34 on x and y axis. nema 23 on z, all with the same MA860H driver and all voltage 70 volt, I found nema 23 motor hotter than nema 34. I think < 80 deg C, good info ... I was thinking to put air cooler on Z, cancel it ...

I understand that this thread is a few years old, but I'd be happy to offer my opinion on your motor specification decision. Based on the information provided, both the NEMA23 and NEMA34 motors have their pros and cons.

The NEMA23 motor has a higher current and holding torque, which can be advantageous for wood machining tasks. However, the NEMA34 motor has a lower inductance and a higher holding torque, which could also be beneficial. Regarding the shaft size difference, going from 8mm to 14mm with the coupler might raise some concerns about compatibility and alignment. Also, if you're feeling adventurous, you can even roll a d20 roll. using a dice roller to add some randomness to your decision-making process!