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IndustryArena Forum > CNC Electronics > Stepper Motors / Drives > CNC ignoramus seeking stepper help
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  1. #1
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    May 2021
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    CNC ignoramus seeking stepper help

    Hi guys, apologies if I've posted in the wrong location or if it's been covered umpteen times already.
    I have absolutely no CNC experience whatsoever, but I'm a tinkerer and love trying to make things just for the hell of it which has led me here.
    I am attempting to make a CNC (for wood and aluminium) measuring approx 600mm x 600mm. I have had a look over a few threads trying to gather info, but I'm struggling a bit.
    I have plans for the machine, but after reading about the stepper motors the plans recommend, they could well be too 'underpowered' and are miles apart (specs wise), they are:-
    1st recommended is a Nema 23
    2.3 v
    2.8 A
    0.83 ohms
    2.2 mH
    The 2nd is a nemá 23
    3.08 v
    3.0 A
    1.1 ohms
    3.6 mH
    I'll be using 4 motors and am thinking of using a DM542 stepper driver for each (as opposed to the TB6600 suggested in the plans) and an Arduino uno 3 (or raspberry pi3??), there's also 2 x SFU1605 ballscrews.
    I have researched other motors and found the following:-
    1st choice nema 24 2 phase
    2.5 v
    5.0 A
    0.5 ohms
    2.2mH
    2nd choice nema 24 2 phase
    1.4 v
    4.0 A
    0.35 ohms
    1.3 mH
    ...my questions are...
    1. Are the nema 24 overkill?
    2. What size power supply should I be looking at for 4x nema 23 or 4x nema 24?
    3. What driver should I use...DM542, DM556 or R60???
    4. Does the inductance really matter that much?
    5. What current, inductance etc should I be looking at?
    Going off a calculator in one of the threads, am I right in assuming the rpms are (respectively), using a 36v power supply...
    1st nema 23 = 876 rpm
    2nd nema 23 = 500 rpm
    1st nema 24 = 490 rpm
    2nd nema 24 = 1038 rpm
    Any help would be much appreciated, please bare in mind I know nowt about CNC etc, so layman's terms please. Thank you.
    Mick

  2. #2
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    Nov 2013
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    Re: CNC ignoramus seeking stepper help

    Hi,
    believe it or not, there is no such thing as Nema24, Nema23 is a known and standardized size, but not so Nema24.

    Nema 23 means that the motor is 2.3 inches square or 57mm. What is commonly refered to as Nema24 is in fact 60mm square.
    So Nema23 is the American (inch units) motor whereas the Nema24 is the metric equivalent. In terms of motor performance there is little
    or no difference.

    All stepper motors lose torque the faster they go, thats just the physics of steppers. The inductance is a resonable measure as to how bad that torque
    degradation will be and therefore limit how fast your machine will be. So inductance is VERY important. Most first time buyers don't know about inductance
    an so buy on the basis of highest torque...makes sense right? Well no, high torque often means high inductance and consequent loss of high speed performance.
    The manufacturers know that newbies buy on torque so they make high torque motors as cheap as possible to capture them but such motors are as slow as a wet week.

    In fact inductance is only part of the picture, the true measure of how fast a motor might be is the 'Inductive Time Constant' which is the product
    of the winding resistance and the winding inductance.

    1st Nema23:
    0.83 x 2.2 =1.826msec
    2nd Nema23:
    1.1 x 3.6 =3.96msec
    1st Nema24:
    0.5 x 2.2 =1.1msec
    2nd Nema24:
    0.35 x 1.3 = 0.455msec

    So clearly the 2nd Nema24 is by far and away the fastest motor you've listed.

    The classical way to make a motor run fast without losing steps is to use the highest voltage you can, I would not limit your machine with a paltry 36V
    drivers. The highest voltage driver commonly available are 80V....get them and run them at 80V....don't mess around...if you want your machine to perform
    then use the highest voltage you can.

    As to the size of the power supply.....that's not quite as straight forward as you might believe.

    Lets imagine you have a 5A stepper motor with a 1 Ohm winding resistance and a 50V power supply. If you hooked up the 50V supply to the stepper
    the current would be 50/1 =50A!!! and it would blow up almost instantly.

    The driver applies the 50V available UNTIL the current reaches 5A AND THEN uses PWM to limit the current to the rated and safe 5A.
    This is where it gets a bit tricky, when the driver goes into PWM limiting the current drawn from the power supply reduces also.
    Output Voltage =5V, Output Current= 5A
    input Voltage= 50V Input current =0.5A

    Yes....you read that correctly....the driver is effectively behaving like a transformer for DC. If you want to read more about this then read the theory
    of how buck regulators work....its fascinating.

    The point is that only for very brief periods of time, micro seconds only, is the power supply required to deliver 5A, for the rest of the time it can loaf along
    at lower currents.

    Most people recommend that you size you power supply to meet the rated current of two (of three) steppers. Thus if you had three 5A steppers then a 10A supply
    is needed. The very heavy current burst required of a power supply are best delivered by a linear supply, that is a mains transformer/rectifier/capacitor combination
    rather than switch modes supplies. Linear supplies are very much more tolerant than switch mode.

    Craig

  3. #3
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    May 2021
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    Re: CNC ignoramus seeking stepper help

    Strange, I replied to your response and its now disappeared!!!!

  4. #4
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    446

    Re: CNC ignoramus seeking stepper help

    I’ll give you my two cents after building a few home machines.
    My go-to stepper for X and Y is nema 23 at about 4” long. Never ran out of power.
    Z can be about half that. Double shafts is handy
    I don’t cut aluminum which is harder on the machine and bits then you think.
    I’m also not cutting with bits above 1/4” as all you need to do is take more passes
    Don’t be tempted to go arduino. Get a real cnc controller and cost more but it’s worth it.
    I’ve used Chinese drives and G540. If you want a strong 4 axis drive that you will never have issues with go with the G540.
    If you can afford it look at water cooled drives instead of routers. They are high speed, much quieter and don’t blow dust all over the place like a router does.


    Sent from my iPhone using Tapatalk

  5. #5
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    Re: CNC ignoramus seeking stepper help

    Quote Originally Posted by Mickyas View Post
    Strange, I replied to your response and its now disappeared!!!!
    What Craig said.

    The 2nd option stepper.
    I also wouldn't bother with DM542 or equivelents.
    I'd get something like the DM860T from stepperonline and use 60V for nema 23/24 sizes.
    80V for nema 34 size.
    https://www.omc-stepperonline.com/di...or-dm860t.html
    Or the Y series:
    https://www.omc-stepperonline.com/di...-34-motor.html
    These can use AC too so you could even just get a toroidal transformer that's equivelent voltage and use that instead.
    I think you'd be looking at around 42Vac direct toroidal in this case but I'm no guru on these.

    I use DM860 drivers on 60Vdc atm with 566oz steppers (3mh inductance) and I'm plenty happy with them.
    I get no lost steps, colossal acceleration, decent max velocity. Just have to check your heat and adjust amperage accordingly.
    Mine actually run pretty cool with their amp rating set as peak on the drivers but I only run them up to 3000mm/min (118ipm) rapids.


    I started out with 36V 'kits' and ended up very disappointed, money wasted.
    Acceleration was poor and limited velocity.

  6. #6
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    Re: CNC ignoramus seeking stepper help

    Hi,

    Are you saying the drivers I mentioned are no good?
    No, I didn't mean that, but rather they have their limitations. As dazp1976 has just posted, he started out with 36V drivers and was disappointed.
    Then he stepped up to 60V and found what he was looking for. He would have spent less overall had he bought the 60V units to start with....but that's the learning curve.

    I would suggest you buy the highest voltage, best quality drivers you can straight up. If you buy right you will still be using them in ten years time, long after the memory
    of the cost of them has faded, whereas cheap and underperforming drives will be a thorn in your side forever.

    Craig

  7. #7
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    Re: CNC ignoramus seeking stepper help

    'Are you saying the drivers I mentioned are no good?'

    It's not that they're bad.
    It's more that you leave yourself with no options.

    You can turn bigger things down if you don't need all of it.....
    You can't turn smaller things up if you do need more.

  8. #8
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    1153

    Re: CNC ignoramus seeking stepper help

    Or the Y series:
    https://www.omc-stepperonline.com/di...-34-motor.html
    These can use AC too so you could even just get a toroidal transformer that's equivelent voltage and use that instead.
    I think you'd be looking at around 42Vac direct toroidal in this case but I'm no guru on these.
    I used this kind driver with 62 vac, easier and cheaper than vdc ... just toroidal stepdown transformer ... motor torque higher and can get faster speed ...

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