i've been browsing ebay for Nema-17 stepper motors, for a future project. The motors i'm looking at are all of a similar size
but have big differences in specification. I'm struggling to understand the relationship between the inputs and outputs.
Below are few key details for a couple of motors i looked at. Motor 2 has far higher voltage, draws twice the the current and yet has practically the same holding torque. can someone please explain this to me?
0.4N.M Holding Torque
12 V, 24 V
45Ncm Holding Torque
Thanks everyone for your responses.
To answer your question directly - a stepper motor's voltage limit is determined by the thickness of the coil wires, and the dielectric strength of the insulation around the wire.
Motor specs can be very inaccurate, especially now that stepper motors have become a commodity item sold by millions of copy & paste sellers who don't understand what they're selling.
That's why you pay more money buying from reputable retailers who guarantee datasheets that are accurate to the part you're buying.
thanks AS_Motion_Lab that was really helpful. sorry for the slow response.
I have recently been looking at Steppers as well.
I have already looked at the arduino link posted below
But it leaves many questions and some things I don't fully agree with or maybe don't understand.
Such as only using a Round object for torque testing
Sometimes you will need a lever and this could be relevant.
Steppers are pretty complicated to get a full grasp of in a short period of time.
Don't know if you have seen these yet or not.
Or how much you know or don't.
I am in no way endorsing this company one way or the other. don't know anything about them
But, their videos explain things pretty well.
https://youtu.be/-ZYQ-GqraLc - Part 1https://youtu.be/xqrbr_6L71Y - Part 2 - all about Torque and Inertiahttps://youtu.be/Y6O9Stcg09E - Part 3
Keep in mind they are using a better Driver
Most hobbyists use the A4988 or DRV8825 drivers
Most 3D Printers use them also.
My guess is the concepts should be close.
Yeah those videos are accurate as far as the general concepts go. LOL I'm scared to look at appendix C.
There are a ton of details you could include when picking a motor, but in the context of printers we can narrow those variables down significantly. What I like most about those videos, is how they discuss the idea of 'system design'. That's the way to go... kind of like running a modern turbo engine... what max boost? ...well what octane, timing, etc... You can't arrive at the highest point of the ladder without knowing which end is up.
This discussion reminds me of when I was in to researching and characterizing brushless dc motors for rc aircraft. There are so many unknown choices out there, some good but most bad. A good approach to finding the good ones requires testing many motors using known repeatable scientific methods. In the context of rc motors, most of that work was done by a handful of passionate hobbyists, who compiled meaningful test results and shared the data publicly. Using that data to choose a motor was a relatively efficient process... there were/are apps and spreadsheets that contained compiled data and produced graphs that could be used to easily find the best motors for a given application... and there was the rcgroup motor community that was very active at pointing folks in the right direction, and sharing new developments in power system testing.
The 3dp community could benefit from better organization of community members who are passionate about motor design. We see lots of shared info with regards to firmware, hot ends, extruder systems, etc... but imho the community is lacking when it comes to someone looking for the best motor for their rig (load, supply voltage, gearing, speed, cooling, driver... all taken in account). Fully understanding the physics inside a stepper isn't for everyone, but that understanding could be better applied in compiling useful info in one place for users to make use of.
Maybe we should start a motor only group that focuses on testing and comparing stepper motors, and presenting that data in a way that is directly useful to most of the community.
Stepper motors are very specialised devices, and so don't make the mistake of assuming normal dc motors rules apply - it is not voltage that is important to control - it is the current that flows to each winding that must be controlled. Steppers can be run at any sensible voltage (typically in the range 5v-50V) provided you drive them via a stepper controller - which will manage the operation of the motor within current limits of the motor. DON'T apply d.c.voltage yourself without a controller because you may select a voltage that exceeds the d.c. current rating of either your power supply or the motor - which won't be good news.
The "NEMA" figure only defines the face-plate physical dimensions (for bracket mounting).
The length of the motor is determined by the number of winding/lamination layers and so hence the motors power/torque/max current, so with all other factors being the same, then these 2 motors would seem to be similar.
The figures you quote are not complete and miss out critical features. I suspect that motor 1 figures are indicative at a set operating point., whilst the figures for motor 2 are 2amps max rating (a very importation figure to know as you will need to encode your controller with this current limit). You need to google the part number and obtain the manufacturers full spec sheet.
Please read up some interesting stuff about steppers and how to valuate.https://www.machinedesign.com/motorsdrives/misconceptions-about-stepper-motors-explained
Try to understand the stepper motor part of the story and the driver part.
When all absorbed, coins will fall in place and you did it all by your self. :-)
There is a lot of good info here: https://forum.arduino.cc/index.php?topic=284828.0
Basically, if you take the same motor and double the DC voltage, you also double the DC current. This says nothing of ac signals which are attenuated more with frequency (ie less torque at higher rpm). So with just those numbers given there is not much to compare. If those were specified as DC values and holding torque, then the first motor is more efficient at 0rpm... but since no inductance or resistance, or even rpm is given, we have just numbers to fill out a meaningless paper.
0.4NM = 40Ncm, now it looks like together
I found this: (so both motor are likely the same)
The simplest is just to connect DC to each winding in turn, via switches (FETs, driver ICs). And in that case, use 4.8V (5V - switch losses) as you confirmed from current and resistance. This is fine at low and medium speeds.
If you need maximum performance, you'll find the motor's inductance attenuates short pulses, so running the motor faster reduces its torque. You can overcome this with a more complex stepper driver, supplying pulses at the recommended 12-24V, to maintain current and torque at higher speeds.
Each pulse is maintained at a high voltage for long enough to build the rated current in the phase, then it should reduce in voltage to the safe level of 4.8V for the remainder of a slow pulse or steady state. This reduction in voltage can either be timed, or achieved by monitoring and limiting the drive current.
So both voltage ratings can be correct : 4.8V continuous, and 12-24V for an optional boost to high speed performance.