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  1. #1
    I am currently considering this kit: https://www.ebay.co.uk/itm/393192724008

    It's a 4 Nm closed loop closed loop stepper, and my intentions are to replace the 1.8 Nm stepper which is used in my "poor man's lathe" project: http://www.mycncuk.com/threads/14589...or-man-s-lathe which I started just for fun and to see if a rotary axis can be used as a simple "lathe" type of machine. It turned out that at least drilling works well, so I continued with this activity and will test even turning probably during the weekend. Currently I manage to run the stepper at 2280rpm reliably but because of the 1:6 gearing, that results in 380rpm on the chuck, which I am well aware of is a bit low, especially for soft material. So I have two changes which I planned.

    1. To replace the gearing with a 1:3 ratio. This will result in double speed, but also half the current torque. Maybe that's still better on soft material than low speed and higher torque, but to compensate the loss of torque, I also plan...

    2. to replace the stepper with a closed loop stepper. In theory, it should mean I get much better torque all the way because the driver compensates for the step loss and applies more current when higher torque is necessary. In theory, I should also be able to run the motor at faster speeds than a stepper motor could run. So the combination of those two is beneficial (higher motor speed and torque), the motor I am aiming at is a 4 Nm motor which is more than twice of the stepper I now use. Of course, I still plan to change the gear ratio also, so with all that, I aim at having around 1000 chuck rpm which would be phenomenal considering this fairly cheap solution.

    I have no experience with closed loop steppers, so I have a few questions.

    Are all closed loop steppers and drivers equal? I don't mean specification wise, but more like quality wise. Does it make a difference who is selling them? What about the drivers? Does it matter which one is used for the same motor? Any pitfalls? I know you prefer AC servos, but currently I am concentrating on DC. I also know there are larger motors which are better suitable for this sort of task, but those are too large for my current ambitions, so I'd like to keep the NEMA 23/24 form factor and also don't want to build or buy a new PSU, so I plan to use my latest 48V 340W DIY PSU, even though the above kit comes with a PSU. Can I trust the torque table? I know it says 1600 microstep, which is wrong since they must mean 8 microstep (1600 steps/rev) but if that is true then at least at 1500rpm I will get much more torque since I intend to run it at 2 microstep (400 steps / rev).

    A last question, which is maybe the most important to find an answer to. The listing says maximum rpm is 2000. I asked the seller if that is true and he replied within an hour (very good response time) that the maximum rpm is indeed 2000 rpm. He did not explain why, even though I asked. The encoder is good for 5000 rpm, so why is there a limit? Or is it possible that the seller does not know everything? I mean, normally, a stepper can be run at almost any speed in theory, as long as the pulses are supplied within the specifications. In theory. In reality, that's different, which is why my stepper stalls at 2400 rpm, but at 2280 rpm it is running happily forever. So why is there a 2000 rpm limit on the closed loop stepper? Is that a built in sort of hard limit? Or is due to something else, or maybe it is like the stepper, after a certain rpm it becomes unreliable, so the seller says 2000 rpm is the maximum, because he knows that it works up to that value?

    OK, many questions and long text, but I hope I can get at least some answers, hopefully at least the last part will get answered, because I would like to increase the speed, and my hope is to be able to run the stepper at 3000 rpm. Maybe that's too ambitious...

  2. #2
    Ok first off Not all closed-loop drives are equal.!! (or motors)

    I haven't used those drives or motors so this doesn't apply to them at all, however, In the past, I have used drives that look very similar (probably come out of the same factory) and wasn't very impressed.
    The reason is two-fold, firstly, compared to the Lichuan drives I use now they gave much rougher stepping action, mostly down to the way they handle resonance I believe.
    Secondly, they gave lower torque at higher RPM, which I believe is down to how they handle the current/volts combined with resonance plus only allowing 50V max. They struggled much past 1500rpm which is where the extra volts come into play, the 4.5Nm Lichuan's I use now will happily shift a 40-50Kg gantry with 10mm pitch screw between 20-25Mtr/min using 55Vac which translates to 2000 to 2500Rpm.

    Regards the motors then most closed-loop steppers are pretty much the same motor as a standard stepper, just with an encoder fitted. It's the drives that make the difference.
    I say most because some are better than others and again I find the Lichuan motors to be made just that bit nicer than some others. Also, you have 3 phase steppers and these are different animals altogether. They are smoother and have more torque and spin faster, unfortunately, you don't find many in nema23/4 with much above 3Nm ratings and 50Vdc drives, that said they will easily match a 4Nm 2 phase using the same voltage.

    On large machines like 8x4, or 10x5, I fit 10nm closed-loop Nema 34's with mains voltage drives and they stop for nothing and spin crazy fast. Much faster than same size 2 phase motors.

    These days I nearly always fit drives that allow AC voltages for simplicity and cost savings, I have run them on both AC and DC using toroidal transformers with smoothing Caps and can see no difference in performance. Now I just hook them up to a 55VAC transformer(toroidal) and away they go.


    Have you considered looking at DC servos.? These spin plenty fast, usually 3000rpm + and give constant torque with lower voltages like 48Vdc.
    Something Like these https://www.ebay.co.uk/itm/283050605...AAAOSwKJhbRIeE

    They are low torque but it's constant across the RPM and they will spin up to 4500rpm with no or low loads. This will work better with your ratios as you'll have far more torque at the higher rpm's than a stepper will have.

    Other than that then I'd say spend a little more and get a 200w AC servo with a brake and do the job right.!
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  3. #3
    Those "DC servos" are closed loop steppers with the driver and encoder integrated into the motor, which is pretty neat. You just supply the DC power (48V or so) and the step/dir signals and it does the rest. These seem to be clones of the Leadshine Integrated Easy Servo family, although I've no idea how well they've been cloned. http://www.leadshine.com/producttype...stepper-motors

    I used a 2Nm Leadshine on the Z axis of my Bridgeport conversion and it's been seamless. Having said that, I've only used proper AC servos since, the last lot being the Lichuan A4 servos that JAZZCNC has been using. They are a bit basic on the software front compared to a Yaskawa but seem to work adequately and are a fraction of the price. You can also swap the cooling fans for something more civilised easily enough if you don't want to have to wear ear defenders(!).

  4. #4
    Quote Originally Posted by Muzzer View Post
    Those "DC servos" are closed loop steppers with the driver and encoder integrated into the motor, which is pretty neat. You just supply the DC power (48V or so) and the step/dir signals and it does the rest. These seem to be clones of the Leadshine Integrated Easy Servo family, although I've no idea how well they've been cloned.
    Don't think they are steppers Muzzer, I have never used any but I've seen them fit on machines and they certainly don't sound like steppers. They sound just like servo's whisper quiet and smooth, plus they spin much much faster. I have used plenty of Leadshine Easy servos which are definitely steppers, 3 phase steppers.
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  5. #5
    Perhaps you are right but there is mention of "1.2 degree step angle" and "closed loop stepper vs open loop stepper" in the description. The photo of the internals also looks pretty much identical to my Leadshine. It's often hard to tell from the websites, as they are often cobbled together from all sorts of random graphics and machine translated Chinglish.

    I see that JMC do both integrated stepper and integrated servo motors in the same mechanical concept, so there ARE some out there. They do a 400W, 60mm, 3.5Nm (pk), 3000rpm true AC servo for about £100 on AliExpress etc, which is starting to sound quite interesting. It's only 48V though, so would need a meaty PSU. It's possible the link earlier is to a JMC or one of its clones of course.

    https://www.jmc-motor.com/product/978.html
    https://www.jmc-motor.com/ntegratedservomotors.html

  6. #6
    Quote Originally Posted by Muzzer View Post
    Perhaps you are right but there is mention of "1.2 degree step angle" and "closed loop stepper vs open loop stepper" in the description. The photo of the internals also looks pretty much identical to my Leadshine. It's often hard to tell from the websites, as they are often cobbled together from all sorts of random graphics and machine translated Chinglish.

    I see that JMC do both integrated stepper and integrated servo motors in the same mechanical concept, so there ARE some out there. They do a 400W, 60mm, 3.5Nm (pk), 3000rpm true AC servo for about £100 on AliExpress etc, which is starting to sound quite interesting. It's only 48V though, so would need a meaty PSU. It's possible the link earlier is to a JMC or one of its clones of course.

    https://www.jmc-motor.com/product/978.html
    https://www.jmc-motor.com/ntegratedservomotors.html
    Ah maybe we are at cross purposes here, I was talking about the link I gave to DC servos which are just like those JMC motors, the link the OP gave was for a closed-loop stepper.
    To be honest it was the JMC I was thinking about but couldn't remember where I'd seen them..
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  7. #7
    Thank you for the advices and answers. I really appreciate your comments.

    There is a lot to be considered and since I have no experinece with closed loop steppers or servo, I really don't know why a weaker servo is more expensive than a stronger closed loop stepper.

    I had a closer look at this one: https://www.omc-stepperonline.com/in...rvo-motor.html

    It is very similar to the one recommended by Jazz, bur it is a Stepperonline version. There is though one difference which immediately is obvious, that is the the Stepperonline version has no enable signal. It is not clear to me when the motor is enabled and when not. I mean, I am actually using the enable signal, and I want to be able to disable it so that I can manually rotate the spindle if I want to, without having to power off everything. It is not clear to me how that can be done unless there is an enable signal. It is also not very clear to me if this is a 3-phase servo or not. The one in Dean's link looks like a 3-phase motor.

    But there is another question... that is about the torque. Both Dean's, and the one here have considerably less torque than 4Nm... so would a closed loop stepper with 4Nm be equal to these two...? I mean, high rpm and smooth, quiet running is one thing and is very nice, but if it is at the expense of less torque then I don't see the benefits. I need this motor to be able to hold the chuck when I use it as a rotary axis, not just rotating fast. So what's the secret? Can these servos be used as ordinary rotation axis steppers also, and can they hold the position when used on the CNC mill?

  8. #8
    Quote Originally Posted by A_Camera View Post
    There is a lot to be considered and since I have no experinece with closed loop steppers or servo, I really don't know why a weaker servo is more expensive than a stronger closed loop stepper.
    The servo at first might appear to be weaker, however, the stepper torque rating is when the motor is stood still, the moment it starts turning the torque drops away, and as the rpm's rise it drops dramatically to the point where at say 1500rpm you will have very little torque left. A servo motor rating is continuous across the RPM so at the rated speed you will have the motor's full torque rating, also they have a peak rating which can be between 3 x and 5x the rated torque for a number of seconds.
    Often this is more than enough to accelerate an axis up to speed before dropping back to the rated torque which again is often enough to drive the axis and then peak again to stop it.
    Then if you apply a ratio like what you will be doing, let's say 6:1, then your 0.6Nm becomes 3.6Nm at the output, and let us say the peak of 3x the rated then you have nearly 11Nm of torque for short bursts of time.

    Now I'm not saying this motor is the answer to your question but if you need speed and torque then you really do need a servo, DC or AC.
    The servos tend to be more money because they are so much more sophisticated in terms of electronics and what can be done with them.

    Quote Originally Posted by A_Camera View Post
    I had a closer look at this one:

    It is very similar to the one recommended by Jazz, bur it is a Stepperonline version. There is though one difference which immediately is obvious, that is the the Stepperonline version has no enable signal. It is not clear to me when the motor is enabled and when not.
    It does, however, this must be done using the RS232 port. Not ideal I know but this one of the advanced features a Servo provides among others. Though I do think it's silly not providing a dedicated enable pin.

    Quote Originally Posted by A_Camera View Post
    It is also not very clear to me if this is a 3-phase servo or not. The one in Dean's link looks like a 3-phase motor.
    The link I gave wasn't a recommendation for that motor but more to show the type of motor, that is a DC Servo motor with integrated drive. After Muzzer's comment, I looked again and agree with him that it does read like it's a Stepper but says it's a DC Servo, these two things conflict with each other because while both uses DC current they are internally structured very differently, so I wouldn't trust the advert description on this.

    Quote Originally Posted by A_Camera View Post
    But there is another question... that is about the torque. Both Dean's, and the one here have considerably less torque than 4Nm... so would a closed loop stepper with 4Nm be equal to these two...? I mean, high rpm and smooth, quiet running is one thing and is very nice, but if it is at the expense of less torque then I don't see the benefits. I need this motor to be able to hold the chuck when I use it as a rotary axis, not just rotating fast. So what's the secret? Can these servos be used as ordinary rotation axis steppers also, and can they hold the position when used on the CNC mill?
    Well without knowing the torque you require then it's nearly impossible to answer, but my gut feeling is that you will need a little more than 0,6Nm and the answer to me is to use either an AC or DC servo with a higher Nm rating and with a brake.
    This will give you both higher RPM you would like and the brake will hold the motor when at standstill. If this was an industrial 4th axis it would have a separate brake to lock the rotation.

    Obviously, this would be more expensive than your stepper setup but it's the only way you will get higher RPM's and torque with reliable results without getting silly about it.
    End of the day a typical 4th axis isn't a lathe, it's not designed for high rpm's but for positional indexing. If you want Lathe performance with accurate indexing then you will need to dig deep as it gets expensive very quickly to do it right.
    (Look for Simpson36 on youtube if you want an idea of how complex it can get.)
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

  9. #9
    Thank you once again. I did watch those videos and seen his work (I am one of his followers) but... There is no way I want to compete with Simpson36 or anyone else. I am too old for competitions, just want to have fun and learn something new. My goal is just that. In the end, if I like it, or see a huge need of a real lathe then I'll buy one. To be honest, I don't think my machine will ever be able to be as good as a cheap 800-1000 USD cheap Chinese micro lathe, even though, mine might well end up being more expensive in the end.

    Regarding the needed torque, honestly, I don't know what I need. All I know is that the current stepper is labelled 1.8Nm, but that's always holding torque. I don't know what the real torque is at 2280 rpm, which is what the rpm is now when the chuck runs at 380 rpm, but it is enough to drill in steel. This weekend I did some turning tests, which was a disaster but not mainly because of the stepper, but because of the extremely weak cross slide I was trying to use. Anyway, I could only turn soft plastic...

    I understand that your link was just an example, not a direct recommendation, but it seems like all 180W servo has about the same parameters. Had a look at JMC servos as well, and also the Stepperonline, but I don't think I want Stepperonline, due to that crazy RS232 enable solution. I don't know how they were thinking leaving out the EN signal and saving one opto coupler, I want a controllable enable/disable, and I don't regard RS232 is equal to that, since I can't use the same signal I am using for the other steppers, so Stepperonline is out of the picture.

    The other thing about the torque is that I want to change the gearing from 6:1 to 3:1 or 2:1 (not decided yet which one) to get higher rpm, so if I do that I will lose torque but gain rpm. Anyway, if those servos are really that good, then I could test with 2:1 reduction, which could give me 1500 rpm on the chuck and about the same torque as I have now with the plain stepper, which should be fine to play with, so right now I am very much tempted to try that out. It's not too late yet to take a step up and use NEMA34, but I would prefer not to, because it would mean a huge change. It would also mean that it starts to become too large for my CNC, which means I might as well give up, which I don't want to do at this stage.

    Anyway, it is fun to test this this out, even if in the end, I will not use it for anything serious, but of course, it would be more fun if I could use it for something as well.

  10. #10
    Quote Originally Posted by A_Camera View Post
    It's not too late yet to take a step up and use NEMA34, but I would prefer not to, because it would mean a huge change. It would also mean that it starts to become too large for my CNC, which means I might as well give up, which I don't want to do at this stage.
    That would be an expensive mistake, large motors like Nema 34's require lots of voltage to spin fast and by lots I mean 150V+ to get any reasonable speed with torque.

    The price of AC servos has come down to such a level that they nearly match High voltage drives which are required to get speed and torque from large steppers. So I would look at those before large steppers.

    I have these 600w AC servos on my plasma machine and while only 1.9Nm they massively outperform the 4.5Nm closed-loop stepper motors. Which at just over $200 is a very good price, I would fit these and pay the extra over the JMC or any of those types of DC servo every time. (They also do them with a brake)

    https://www.aliexpress.com/item/3304...5be81468ni78om

    Like I said before if you are going to go this far then do it right the first time because while digging deep hurts I always find it works out cheaper than experimenting and far less hassle.
    -use common sense, if you lack it, there is no software to help that.

    Email: dean@jazzcnc.co.uk

    Web site: www.jazzcnc.co.uk

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