Stepper Motor Torque Choosing Stepper Motors

Hi, sorry if I'm putting this in the wrong place but I'm new to the forum.

Back in 2016 I built a Mendel90 with a Gen7 1.5v mother board and used stepper motors from 2 old Beckman dot matrix printer plus I had a extra stepper motor as a spare. The stepper motors I have are Astrosyn 17PS C026-02. I've looked online for a datasheet but could not find one. I think these stepper motors only have 28 N-cm holding torque.

I have looked through the Mendel90 documentation and online but can not find any were that it mentions what size stepper motor or what holding torque I should use for the X, Y, Z and E stepper motors.

I would like to know if anyone out there knows what holding torque (N-cm) I should use for the z-axis motors.

Also I would like to know what holding torque (N-cm) I should use for the extruder without the big gear. I would like to do direct drive of the filament.

Does anyone have any idea?

Thank you, Kenn.

the duet wiki has an excellent article on motor choice and the reprap forum as well (but older)

Hi Sungod3k, thank you for the reply.

I did find the Duet wiki page :
Duet Wiki choosing a stepper motor

When I was younger I worked for a company that manufactured stepper motors so I have a little back ground in them. It did take me a few times going through the page to under stand what they were getting at, but for a newbe it might be over welming.

I find that most of the documentation says to get Nema 17 but there are several models most are 1.8deg. at 200 steps, no guessing there.

I did find a starting point on the RepRap Stepper Motor wiki page.
RepRap Stepper Motor wiki

It states "The Mendel officially requires approximately 13.7 N·cm torque (19.4 ozf·in) of holding torque (or more) for each of the X, Y and Z axis motors to avoid issues," ,
but still no mimum torque requirements for the direct drive extruder.

I did measure the torque on the Astrosyn 17PS-C026-02 stepper motor I got out of the Beckman dot matrix printers. They had around 0.9466 N-cm torque, it's so small that I can stop them easly with 2 fingers when running.

I figure I'll start with Nema 17HS15-0404S, they have 26N-cm torque, 12 volts at 0.4A and are low cost around $7 each + shipping. They should work for the z-axis and extruder.

Thank you, Kenn.

That may not have enough torque for a direct drive extruder. I'm using this one which has around 175 N-cm.

Don't go for a 12V 0.4A stepper, it is a very bad match for the constant current drivers used in repraps. Look for a motor which needs between 2 and 4 volts and has a rated current around 1.3A.

26Ncm torque is enough for an extruder with 3:1 gearing, but as @etfrench says, not for a direct drive extruder.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
etfrench
That may not have enough torque for a direct drive extruder. I'm using this one which has around 175 N-cm.

That is way overkill (unless you want to cold extrude 3mm filament ) and in fact so heavy that you will need bigger motors to move the gantry if you want to achieve decent speed. Besides the hobbed gear will be the limiting factor..

Edited 1 time(s). Last edit at 03/23/2019 04:01AM by MKSA.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Quote
dc42
Don't go for a 12V 0.4A stepper, it is a very bad match for the constant current drivers used in repraps. Look for a motor which needs between 2 and 4 volts and has a rated current around 1.3A.

26Ncm torque is enough for an extruder with 3:1 gearing, but as @etfrench says, not for a direct drive extruder.

True, this is a bit too weak but the NEMA 17 40mm long 3.4V 1.5A with 45 N.cm will do. Just need a small diam hobbgear (around 9mm dia). Simple and cheap for a start.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

To add to the excellent advice given, the driving voltage needs to be sufficiently high to get the rated torque. It should be around 2.5 to 10x the rated steppermotor voltage. It's a balance between torque and running the motors cool enough.

When I upgraded from a ramps with A4988 stepsticks at 12V to a duet with tmc2660 at 24V I got much more torque and the steppers ran 3-4x faster before stalling. This is with nema23 steppers originally ment for cnc.

I use nema17 2.5A steppers for the extruder. I've set the motor current to 1.8A. it runs quite hot at around 40-50 degrees but it has a lot of torque and can move quite fast for retractions without skipping steps/stalling. I use 1:3 gearing. I use a long 3mm inner diameter bowden tube that needs about 5-6mm retraction. The quicker it can retract the smaller the blob at the spot where it retracts.

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Kind regards
Imqqmi

NFAN CoreXY printer:
[reprap.org]

Thank you for all the good advice, but I didn't think anyone was going to answer after 200 viewings so I bought the Nema 17HS15-0404S.
Not a total loss they were only $7 with free shipping, total of $21 dollars. I guess I'll use them for the z and y axis.

The extruder setup I'm trying to do is a MK8 with Bowden tube in order to keep the weight off the y_axis. I have the MK8 attached to a piece of angle iron attached above the y_axis.

I did find some info on the MK8,
http://www.geeetech.com/wiki/index.php/MK8_Extruder]http://www.geeetech.com/wiki/index.php/MK8_Extruder[/url]

in the MK8 documentation it states they use a 42BYGHW818 stepper motor, but I couldn't find a datasheet to tell me what the Ncm holding torque was. I did find a datasheet for the 42BYGHW811 which has a holding torque of 50 Ncm. So I'm guessing the 42BYGHW818 should have around 60 or 65 Ncm holding torque.

The filament I'm using is 1.75 ABS and PLA.

The Gen7 1.5v board uses a 12 volt buss that's why I choose the 12 volt stepper motor. The DRV8825 stepper motor driver says it can handle 7 - 47 volts but I don't know if it sets it automaticly or if I have to set it in the Marlin firmware. Plus the DRV8825 can handle current up to 2.5 amp. The stepper motor I'm getting only uses 0.4 amp so I figure it would keep the DRV8825 cooler.

I use the Mighty Core bootloader and Marlin 1.1.9 firmware, plus I upload it using the Arduino IDE 1.6.7 through a Arduino Uno to a ATmega1284 (non-P) chip. Since the guy on the Arduino forum fixed the Marlin firmware for the ATmega1284 (non-P) I've been able to upload to the chip over 30 times without any problems.

Thank you, Kenn.

To get good performance from 12V stepper motors you will need at least 24V power. The reason is that the voltage rating of the motor is the voltage it needs to provide the rated current at standstill. When they are moving at significant speeds, they need higher voltage. You can calculate the voltage that the motors need at speed using the motor EMF calculator at [reprapfirmware.org].

Edited 1 time(s). Last edit at 03/23/2019 05:36PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hi Dc42, thank you for the reply.

So what you are saying is to use a low voltage, higher current stepper motors for the x and y axis because they need the speed. The z-axis doesn't really move all that much during operation maybe 1mm at a time.

The Mendel90 https://reprap.org/wiki/Mendel90

Thank you, Kenn.

Quote
KennTech

The Gen7 1.5v board uses a 12 volt buss that's why I choose the 12 volt stepper motor. The DRV8825 stepper motor driver says it can handle 7 - 47 volts but I don't know if it sets it automaticly or if I have to set it in the Marlin firmware. Plus the DRV8825 can handle current up to 2.5 amp. The stepper motor I'm getting only uses 0.4 amp so I figure it would keep the DRV8825 cooler.

The DRV8825 doesn't know anything about the voltage (voltage limit is probably related to the trace sizes). It only cares about current. You'll need to set the current before connecting your stepper to it.

Hi Etfrench, thank you for the reply.

So what I getting from you is that the DRV8825 doesn't change the voltage coming from the 12 volt buss. It sound like if I plug one of these low voltage stepper motors in to the 12 volt buss that it would fry.

I can adjust the DRV8825 current but it is still going to put 12 volts to the stepper motor.

Thank yoou, Kenn.

No, that's not how they work Generally speaking, you can use any voltage up to 10X the rated voltage. The current cannot exceed the rated current. See dc42's earlier post about the EMF calculator.

Quote
etfrench

The DRV8825 doesn't know anything about the voltage (voltage limit is probably related to the trace sizes). ......

WRONG !

Edited 1 time(s). Last edit at 03/24/2019 05:08AM by MKSA.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Quote
KennTech
.... 42BYGHW818.....

Just measure the coils resistance. If it is around 4 ohm, it is OK.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Quote
etfrench
See dc42's earlier post about the EMF calculator.

As nice as it was for dc42 to show me the EMF calculator, it only has 3 printer geometry and none are the Mendel90. I did save it for later use if I build a Delta printer. Plus I don't have the money to buy a 24 volt power supply. The 12 volt power supply was free out of a discarded computer.

Right now I'm not looking for speed so much but quality in a print. Once I have this printer running I can print the parts for a new machine.

I'm disabled so not a lot of money to go out and buy new parts.

I've had a heart attack, double by pass heart surgery, Chronic Obstructive Pulmonary Disease (COPD), angina and the beginnings of diabetes.

I want to build a InMoov Robot and make it as a surrogate so I can still do things if I get stuck in a bed or wheel chair.

Thank you, Kenn.

Mendel 90 is a Cartesian printer, so that's the setting to choose in the motor EMF calculator.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hi Dc42, thank you for the reply.

I found this web page that goes into a little more detail about the dynamics of stepper motors there voltages and current.

An interesting explanation about steppers voltage rating

I'll see if I can find other pages that talks about the stepper motor voltage ratings. This will help with the EMF calculator.

Thank you, Kenn.

Here's a web page that explains it even better.

http://blog.inventables.com/p/stepper-motors.html

Let me restate that to say that the driver isn't going to destroy itself or the stepper as long as the current is lower than the max specified current of the stepper and the voltage is less than 10X the specified voltage of the stepper.

So Dc42 what you are saying is to look for the lowest EMF volt rating for any given stepper motor. Is that correct?

Quote
KennTech
So Dc42 what you are saying is to look for the lowest EMF volt rating for any given stepper motor. Is that correct?

Not quite. Low EMF/low inductance comes with high rated current, and if that rated current is too high then the stepper drivers on your controller electronics won't be able to drive the motor adequately.

Stepper motors in 3D printers are typically run with a peak current of between 60% and 85% of rated current. More than 85% and they get too hot; less than 60% and you would have been better off choosing a less powerful motor (and the microsteps may be less even). You need to make sure that the stepper drivers on your controller electronics can handle a peak current in the range 60% to 85% of the motor rated current.

The considerations go something like this:

1. What current are your stepper motor drivers comfortable with? This varies from about 1.0A (plug-in TMC2130 drivers) to 2.4A (TMC2660 drivers on a Duet WiFi). Or even higher if you use external stepper drivers.

2. How much torque do you need from the stepper drivers? 25Ncm is enough for most small 3D printers, except for ungeared extruders. Larger printers with heavy print heads and direct drive extruders may need more.

3. Are you using 12V or 24V power? 24V gives you more options. Modern printers such as the Prusa i3 Mk3 and the Ender 3 use 24V.

4. Based on #1 and #2, select a motor with a suitable torque and rated current, then factor in #3 to work out whether it will give you the speed you want.

Edited 2 time(s). Last edit at 03/25/2019 05:43PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hi Dc42,

Well my power supply is 12 volts and the DRV8825 driver boards can go to 2.5 amps. So I guess I'll look for motors that are up to 2 amps and around 2 to 4 volts.

But I'll have a time trying to find them not to many chooses online.

Thank you, Kenn.

There are tons of NEMA 17 steppers to choose from online. I'm using these from StepperOnline on my delta printer and on my rose engine. All of them are using the DRV8825 drivers set to 1.5A. Current price is around $10US.

Quote
KennTech
Hi Dc42,

Well my power supply is 12 volts and the DRV8825 driver boards can go to 2.5 amps. So I guess I'll look for motors that are up to 2 amps and around 2 to 4 volts.

But I'll have a time trying to find them not to many chooses online.

Thank you, Kenn.

Gee, you are making a mountain out of a molehill.

They are easy to find as they are currently the most common ones (Aliexpresss, Banggood) due to the demand for these 3D printers and plywood CNC !

In the past, in older machines like old printers, scanners with less stringent requirments and the use of simpler driving circuits, they were made and rated for the power supply used (12V or 24V). Most not even hybrid steppers.
In fact I made a geared extruder with one of these PM 35mm stepper. It worked fine BTW.

As I wrote, just measure the coils resistance, around 4ohm or less, it is OK.

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"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)

Quote
KennTech
Well my power supply is 12 volts and the DRV8825 driver boards can go to 2.5 amps.

DRV8825 drivers on little plug-in boards will not go up to 2.5A because the PCB heat sinking area is much too small.

With those drivers and 12V power, I suggest you look for motors with around 1.68A rated current. There are lots to choose from with that current rating.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
MKSA
Gee, you are making a mountain out of a molehill.

All you guys have been through tough dissisions of selecting the parts for your 3D printers.

You took chases made mistackes and made corrections, you've figured out what works and what doesn't work.

You have the knowledge that I lack, I'm trying to obtain the correct knowledge. So I can make as few of mistackes as possible and a informed purchase.

This will also help other folks who don't get the documentation that is out there.

Sorry if I'm fustrating anyone.

Thank you, Kenn.

I found this one on Stepperonline: ]Nema 17 Bipolar 1.8deg 36Ncm (51oz.in) 1.68A 2.8V 42x42x39mm 4 Wires

It's the only one close to dc42 description and they only sell it from China.

Why do you think that one will work better than the 84 oz-in? If both are run at 1.5 amps, which will have more holding torque? Which has better phase resistance and inductance?