I am looking to upgrade my original X-Carve NEMA 17 motors to NEMA 23 motors. I currently have an X-Controller. I’m trying to get an idea of what will and will not work with my equipment.
In another posting @JustinBusby said that:
What does it mean that it has “a lower inductance which pairs better with the 24V of the X-Carve”? Or, at the very least, what specifications am I looking for in a stepper motor to make sure it pairs better?
Thanks,
Jim
The spec sheet of a stepper motor will list an inductance value on them, usually in mH (milliHenry).
There’s a lot of stepper motor theory (https://www.geckodrive.com/support/step-motor-basics.html is a great read, Section 4 covers inductance) as to how inductance relates to operating voltage but it boils down to the operating voltage is setting an RPM limit of useable torque while the stepper is turning.
The lower the inductance, in general, the flatter the torque curve at low RPMs meaning you maintain more torque and don’t get power output limited.
Does this REALLY matter on the Xcarve? I think it does but the math says maybe not.
1500 mm/min (~60ipm) is an RPM of 37.5:
(40 mm/step) / (1600 steps/rev) = 0.025 rev/mm
0.025 rev/mm * 1500 mm/min = 37.5 rev/min
Looking at 2 torque curves (3.6mH inductance vs 5.4 mH inductance), realizing one is 24V and half step, the other is 1/8th microstep at 48V, looking at around 100 RPM (still over 2x higher)
3.6 mH @ 24V 1/8 microstep is about 138 oz-in (half the graph value)
5.4 mH @ 24V 1/2 microstep is about 155 oz-in
Now microstepping is at play. 1/8 microstepping has less incremental torque than 1/2 microstep so you could say the 3.6 mH value at 100RPM will be higher and probably on-par with the other motor.
Much higher RPM values makes the difference much larger.
All that being said, I did some tests awhile back (Z Axis Acceleration Tuning - #13 by JustinBusby) and found that 2 similar motors (269 oz-in and 270 oz-in) when used on my linear Z had a 15 ipm difference in their max rate value.
What does it all mean? Essentially get what you want and is cheaper because at our speeds, it doesn’t really matter. I’m just an engineer that likes the theory and for $3 more per motor got the lower inductance one.
Majority of Xcarve users won’t go over 60 ipm so most don’t need to worry so does a 3.6 vs 5.4 mH actually matter? And we’re only talking the X and Y at those RPMs.
At speeds 120+ ipm, then it starts to matter more and not to mention, based on the tests I did for a Z axis, it def can matter there.
And it’s all theory and not real world.
I’ve had great success with my 3.6 mH 270 oz-in motors and a warm fuzzy that it is ideally better.
I’m an engineer. I like to know the math and what should happen and then do whatever I want as long as it works and ignore what analysis says should happen.
Make sure the ones you get are not over the current capacity of the controller.
I have bought a 290 oz-in one and its fine for the controller I use. I bought it because I was having issues with the X axis as I have a heavy spindle on it. Its about 9lbs which is more than the router. Also I had some extra deflection from the dust collection hose as its adds a bit of tension. Below is the link to the one I purchased
https://www.amazon.com/Stepper-Motor-Bipolar-269oz-Router/dp/B00PNEPI0A/ref=pd_lutyp_rp_7_2/130-4347198-1472461?_encoding=UTF8&pd_rd_i=B00PNEPI0A&pd_rd_r=554ae635-3505-4f7c-8e44-2317ff72e2f9&pd_rd_w=jj1Uh&pd_rd_wg=Y3RiP&pf_rd_p=a4e8f244-37b2-46ab-9332-ab1ac63f3abd&pf_rd_r=C3NG26YCGBBHWFZ8Z61T&psc=1&refRID=C3NG26YCGBBHWFZ8Z61T
Thanks everyone for their feedback on this.
@StephenCook as far as not going over the current capacity, that actually seems difficult to do with any reasonably sized (for an X-Carve) stepper. The X-Controller is rated at 4A per phase and most steppers that I have seen and considered at are 3A or less. But, still, good to remember.
Now, if I was to consider this stepper:
The specifications says (emphasis mine):
Motor Type: Bipolar Stepper
Step Angle: 1.8 deg
Holding Torque: 1.9Nm(269oz.in)
Rated Current/phase: 3A
Voltage: 3.36V
Phase Resistance: 1.12ohms
Inductance: 4.8mH ± 20%(1KHz)
The voltage is 3.36V??? I thought the steppers were driven at 24V (in the case of the X-Controller). Is this a number I need to be concerned about when choosing a stepper, or is this like the inductance and it doesn’t really matter for our rigs?
Thanks again,
Jim
No. The stepper driver controls the current to the stepper, so the voltage rating don’t really matter.
I use the same steppers for the Y that came with my x-carve.
I didn’t upgrade them as there is 2 of them vs 1 on the x.
The ones from inventables are 3.2v which isn’t that far off.
Also note: I am using a Gecko 540 now. No x-carve controller.
But my Y steppers, as well as X & Z, are from my original Shapeoko 2, so I only have NEMA 17 steppers. That’s all they engineered for back then. Probably made sense considering that they only shipped with a Dremel knockoff also.
Other than my steppers, everything about my current rig is just like a modern 1000mm X-Carve, including the DeWalt router.
I figure if I am going to upgrade, I might as well make them all NEMA 23 steppers.
The driver manage the voltage thing - no worries.
It “steps down” in effect the 24V input to a manageable level for the stepper motor.
anyone find issue upgrading to 260oz motors with shaft too short to align pulley ? how did you correct this
did you have issue with shaft being shorter and aligning pulley the 140oz steppers are 24mm the one you got is 21mm?
If the lacking 1/4" of shaft length prevent you from securing the pulleys etc your only option is to replace steppers with new ones with long enough shaft.
how did you get yours to work same cnc ? you got the 21mm shaft ones correct
I bought my system a while ago but I did not have any issues with shaft length. Getting new steppers with correct length shaft is the recommended option.
finding them is issue anyone have link to 269oz motors with near 24mm shaft
