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Author Topic: How to identify a stepper motor  (Read 2396 times)
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Poty
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« on: December 20, 2021, 09:59:45 21:59 »

Dear friends:
I hope this timeof the year find you in good health and wealth.
I have a great problem (or a great misunderstanding) with stepper motors. I have a little project running about driving one of this, and I want a certain power, so I chose a Nema 17 one. When looking for characteristics, well, I had to learn about frequencies, currents and voltages applied to those ones, its pole resistance, bla bla bla, nothing out of this world... But then, when I decided what I was looking for... BAM! just a couple of datasheets, one from Germany, another from china, and nothing more.
I do suppose that being under NEMA normalization, something will be clear if I read Nema pages... Another crack in my skull.
So, even that I try not to disturb you with my baby questions, I have to, because Im lost.
Can, please, anyone send me a reference, little guide, whatever that help me in this mess?
Until now, The only thing that I certainly defined is that Nema 17 fixes the square size of the face plate, and the diameter and position of the screws to mount it. All electrical properties depends on the maker.
I only need info on bipolar stepper motors. But all references are welcome.
Thanks in advance, from the fourth world....
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vern
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« Reply #1 on: December 21, 2021, 08:36:26 08:36 »

even after reading your post twice I can not figure out what you want to know.
As you already found out: NEMA 17 is only a standard for mechanical properties.
Everything else is up to the different manufacturers, like current, voltage, stepsize etc.
You just have to pick one, depending on your application.
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Xwing
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« Reply #2 on: December 21, 2021, 09:05:37 09:05 »

I have a great problem (or a great misunderstanding) with stepper motors.

The acronym NEMA 17 indicates only the mechanical characteristics of the motor mounting flange, it has nothing to do with the electrical characteristics.
Unfortunately for low-cost steppers, especially Chinese ones, it is difficult to find complete data sheets.
Keep in mind that the actual power of the stepper depends on both the current and its size.

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devetka
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« Reply #3 on: December 21, 2021, 05:24:00 17:24 »

Can, please, anyone send me a reference, little guide, whatever that help me in this mess?

as already mentioned, reference for NEMA17 is only the face plate, so center cylinder size, hole mount and that is it...

All electrical properties depends on the maker.

exactly, and if you are not geting some reputable brand but ordering from PRC the electrical properties they adverties are for reference only, they have nothing to do with real data.

but do not despare!!

there are only few important aspects of the stepper motor
- inductance
- holding torque
- running torque
- current
- rotor inertia

Inductance you can measure with any decent LCR meter. With inductance you can then calculate maximal speed without torque drop

Torque will depend on the length of the stepper and some other parameters, since you already have a motor, who cares, plug it in and see if it has enough torque or not, if it stalls it dont Cheesy .. of course you can measure the torque too you can find ton of videos online on how to do it

Rotor inertia - this is important if you have really high acceleration and often speed changes, I have no clue how to measure this but again since you can not change it on the motor you already have who cares

Current - this is the most important aspect you need to know to get most out of your motor. You drive motor with current, not voltage, so even when motors do have voltage rating that is completely useless info. You want to know maximum current you can pass through the motor. This is rather simple to get to - more current you pass through motor more motor will heat up. Max safe operating temperature for the motor is around 70C but for e.g. I target 50C to be on the safe side. Increase current your driver is driving your motor with untill your motor is running at around 50C and that is your max safe current for your motor.

I am using this technique for 10+ years building robots, 3d printers, cnc machines and it never failed me. You look at parameters when you are purchasing motors, and if you need to get motor with certain parameters just forget PRC and get decent ones from Germany or Sweden or Japan ... but if you already have some, it is rather easy to determine how to drive them as wrt max voltage the limit will be your driver and not the motor, current limit you get to by measuring temperature... everything else you can not change so who cares..
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Poty
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« Reply #4 on: December 24, 2021, 11:47:19 23:47 »

Thanks you all for your answers. Those confirm my original suspicious. Just the maker will give me the adequate response. I thougt that maybe NEMA will define an electrical standard too, so my questions.
Anyways, the most important question as a programmer.... Does anyone know the frequency limit for a bipolar stepper? I mean, the maximum rate of polarity changes that a stepper can accept before stalling?
I saw a few formulas online to calculate those, but those uses specific motor parameters, like those you mentioned in your answers before.
I love math, but hate when I cant get the necessary data. Plus, the steppers that I`m using (in a 3d printer) came with no identification, just NEMA 17 characteristics.
This is the key question.
Thanks in advance, I hope you have a Merry Christmas.
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vern
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« Reply #5 on: December 25, 2021, 09:46:02 09:46 »

Quote
Anyways, the most important question as a programmer.... Does anyone know the frequency limit for a bipolar stepper? I mean, the maximum rate of polarity changes that a stepper can accept before stalling?

again, this depends completely on the manufacturers data.
They list the maximum steps per second in their datasheet. Of course it all depends also on the voltage, the current and the load you have on the motor.
Of course it also depends on your software, you have to ramp up the frequency to go to full speed, if you don't it will not move at all under load.
Steppers are very tricky, I would recommend buying a cheap evaluation kit and check out some motors and their properties just to get some experience.
You could also tell us what you want to do with your steppers so we could recommend some designs and some motors that might suit you.
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devetka
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« Reply #6 on: December 25, 2021, 05:43:34 17:43 »

Does anyone know the frequency limit for a bipolar stepper? I mean, the maximum rate of polarity changes that a stepper can accept before stalling?

There is no limit. If you can overcame the back emf you can spin it as fast as you want till the darn thing blows apart from centrifugal forces Cheesy

You can use online calculators, e.g. I commonly use this one  https://www.reprapfirmware.org/emf.html

geometry - cartesian (so you get direct relation for your motor rpm)
supply voltage - here you can test different voltages
motor current - here you can test current
req. max. speed - set this to some super high value
number of motors in series - 1
motor properties: step angle, use 200steps as simplest to calculate, torque - irrelevant, current set same as motor current from first line, resistance and inductance measure and plug in real values
drive microstepping = x1
drive axis = leadscrew M6 1mm (easiest calculation)
this will calculate you 200 steps per mm, your motor is 200 steps/rev so 1mm equals 1rotation so 1mm/min = 1rpm so you can easily calculate rpm from speed in mm

now you play with the numbers Cheesy ... most NEMA17 motors can handle up to 2.5A for a short while but max amperage you measure by temperature as it will also depend on the way your driver is driving the motor (not all drivers are the same)

the max speed are the two bottom lines in the calculation, speed at with torque starts to drop - this is your max speed, after that speed back EMF is higher than your supplied voltage and you can not overcome it so your torque will start to drop


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Poty
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« Reply #7 on: December 31, 2021, 11:59:33 11:59 »

Well, that calculator made my day!!! Because the lack of information about those pap that I`m using, I took all those that I can measure (resistance, number of steps, and so), invented some (inductance and torque) and got results pretty similar to those who Im suffering with my application. More than 80mm/s paps arent fine., They starts to loose torque. and got max frequencies too: Aprox 38khz. Thank you!
Well... today is the last day of the year. I hope you can enjoy a good dinner with your family and loved ones.
Happy New Year!
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devetka
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« Reply #8 on: January 01, 2022, 06:00:25 06:00 »

glad I could help Smiley, thanks for the wishes, I wish you all the best in new 2022

that calculator really helps a lot both with existing motors and to chose motor when purchasing them... also when designing stuff so good bookmark to keep Smiley
it also explains how you can set your drivers to use more and more current but nothing happens and even pushing 10A into 1A motor do not work as your motor voltage is too low for the speed you want to achieve... so far I tried so many drivers for steppers it hurts ... almost all alegro has to offer, all kind of hitachi, texas instruments drivers both DSP and regular ... bunch of fancy arm32 based software drivers and out of everything I tried so far TMC are my favorites. They do not support as high voltage as some other drivers but for these small motors they have the best product range to choose from and the prices are decent for small hobby quantities that is also important as number of others are available only for high quantity orders
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