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IndustryArena Forum > CNC Electronics > Stepper Motors / Drives > Chinese stepper motors, how many steps?
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  1. #1
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    Chinese stepper motors, how many steps?

    Hi everyone,

    I was hoping someone could shed some light for me on the stepper motors that come with the Chinese 3040 machines. I'm tired of the "guess and check" method for getting the motors tuned in Mach 3 and I'd like to get them as accurate as I can. Obviously, I can't do any calculations without the number of steps on these motors.

    I've tried to count the steps but it's pretty hard to accurately count, since it's easy to overturn the hand wheel and go two or three steps further. I ended up counting near 100 steps. I'm not sure if it would ever be standard for a motor to have, say, 104 steps, or 97 steps. So I figure by counting and getting a number that is fairly close but maybe not perfect, I might be able to assume these are 100 step. Would it be safe to make this assumption?

    Does anyone else use these motors, and have you confirmed how many steps the motors have? I forget what the micro step setting is on the driver (James Newton drivers, super awesome drivers!) but that is much easier to determine.

    Thanks!

  2. #2
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    Re: Chinese stepper motors, how many steps?

    Most standard stepper motors have 200 Steps/Revolution, these will often be marked with 1.8 degrees/step on the motor. There are some steppers that have 400 Steps/revolution these will be marked with .9 degrees/step on the motor. Those are the two most common type available.

    Russ

  3. #3
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    Re: Chinese stepper motors, how many steps?

    Quote Originally Posted by CNCMAN172 View Post
    Most standard stepper motors have 200 Steps/Revolution, these will often be marked with 1.8 degrees/step on the motor. There are some steppers that have 400 Steps/revolution these will be marked with .9 degrees/step on the motor. Those are the two most common type available.

    Russ
    Oh, OK that's what the 1.8 means, thanks Russ! One of the motors had a sticker on it with 1.8, thanks for explaining that. Now just so I'm clear on the calculation, it will be 200 x (whatever the micro step setting is) / the pitch of the lead screw, right? (I believe the lead screw is single start)

    EDIT: Ok I looked at my leadscrews, they're more than likely metric, since I'm counting nearly 13 threads per inch. That's not a common imperial pitch, but I'm not sure what the metric pitch is. I'll have to take the nut down to the hardware store and see if they have anything that matches. I'm thinking it's a 2mm pitch.

  4. #4
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    Re: Chinese stepper motors, how many steps?

    YES,
    If you look at the FREE online copy of the MACH3 software manual they will show you how to calculate steps per unit. 200 p/r * micro stepping selected 4x, 8x, 16x, etc. Then if you have a ballscrew the the number of turn per unit like inch.

    Example calculation:

    Motor: Panasonic Servo 2000 P/R
    Gearhead: 11/1
    Ballscrew: 5 Turns/inch

    2000*11*5 = 110,000 pulses per inch

    Another Example: Using Metric Ballscrew

    Motor: 2500 Pulses/Rev
    5mm ballscrew > 1"/.196845 = 5.08 turns per inch.... 5mm = .196845" much keep in the same units for all calculations

    2500*5.08= 12,700 pulses/inch

    These were servo calculations which have higher number of pulses per revolution, but the stepper works exactly the same way.

    Russ

  5. #5
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    Re: Chinese stepper motors, how many steps?

    Awesome, glad I at least understand the math. Thanks again for the explanation. Once I figure out the lead screw pitch I should be good to go!

  6. #6
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    Re: Chinese stepper motors, how many steps?

    Well, I'm at a loss. After doing all the math, my situation has not improved! I used the formula the Mach 3 manual explains, which is "steps per rev * motor rev per unit". I also found a steps per calculator on Mach 3's forum, and my math and the numbers spit out by the calculator are the same.

    X axis = 10 microsteps, 1000 steps per unit
    Y axis = 8 microsteps, 800 steps per unit
    Z axis = 16 microsteps, 1600 steps per unit

    These numbers completely throw the machine out of whack. For the sake of ease, I'll convert to inches here...when I move the machine an inch, it actually moves closer to 1.5". When I guess and check and use the steps per calibration mechanism in Mach 3, I can get accuracy down to within .002", according to my dial indicator. I tell the machine to move an inch, and the needle ends up in almost the exact same spot, no more than one notch (.002") off. Same when I move it back. If I move it 2", I get the same result. Pretty happy with that accuracy, except I lose accuracy during actual cuts.

    When I run a test job, and cut a 7" rectangle, I end up with a rectangle that is 7 1/8" long. Or a 4" circle ends up being 3 7/8". I don't know what to look at to tighten up the accuracy...can someone suggest where I need to look/research/measure/whatever in order to get more accurate? Maybe the spindle isn't perfectly plumb with the table? Maybe the spindle is too heavy and the machine can't move it..? (Unlikely, since I've watched the machine haul butt across the table with the spindle and doesn't stall or complain or anything.)

  7. #7
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    Re: Chinese stepper motors, how many steps?

    You have not taken the ballscrews into your calculations

    You only show the stepper and micro stepping

    Russ

  8. #8
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    Re: Chinese stepper motors, how many steps?

    Sorry, here's the calculator I used where I included the pitch of the screw:

    https://www.machsupport.com/forum/in...?topic=16315.0

    So (200*microstep)/2 gave me the numbers above. Either way, it turns out the guess and check method yields very good results and I have to believe that isn't the source of my problem. I need to figure out why the movement is dead on when I'm in MDI, but as soon as I run a test job the cuts are off. I'm inclined to think it has to do with cutting action and flex. I read somewhere that climb milling can cause tool movement, etc.

    I mean the cuts are in the ballpark, but I have a few projects ready to go but I don't want to cut anything until I can get a bit more accurate. I'm hoping that's not a pipe dream with a Chinese machine.

  9. #9
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    Re: Chinese stepper motors, how many steps?

    The pitch on the lead screw is (probably) 5mm. It's the same on the 3020 and 6040 machines (I have a 6040)
    The metric example on the calculator spreadsheet is what you need to use. i.e. (200*microsteps)/5

  10. #10
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    Re: Chinese stepper motors, how many steps?

    Oh, interesting. I don't quite understand how to measure the lead screw then...from thread crest to crest is 2mm, but I assume for metric that isn't how one measures the pitch.

    So let's examine my z-axis. Right now, steps per is set to 499.9something...basically 500. Micro step set at 16, and it is accurate to within .002". When I use the calculator and the 5mm pitch figure, I get (200*16)/5 = 640. Now, I haven't plugged in 640 into the machine yet. I'll definitely try in a little bit and see what happens, but I don't understand how the machine is accurate on 500 steps per unit. That would mean my micro steps are 12.5, which isn't a possibility! Either that, or the pitch is actually 6.4. Also unlikely!

    Maybe when I plug in 640 it will retain accuracy, I have no idea. That would be awesome. But even with a 5mm pitch, the math all makes sense until I actually apply it to the machine. I'll give it a shot though and see how the machine reacts.

    Thanks for the tip on the 5mm pitch! I'd assume these screws are single start?

  11. #11
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    Re: Chinese stepper motors, how many steps?

    When you use metric ballscrews which is what almost all Chinese machines use, the calculation will be as follows"

    10mm ballscrew =.393", so 1/.393" = 2.54 turns to move one inch.
    5mm ballscrew = .19685, so 1/.19685" = 5.08 turns to move one inch

    Z axis = 16 microsteps, 1600 steps per unit

    200 step/rev * 16 * 2.54 = 8128 step/inch: If you are using a 10mm ballscrew

    or

    200 steps/rev * 16 * 5.08 = 16256 steps/inch : If you are using a 5mm ballscrew


    You are using 500 steps/unit on your Z axis and you say it is accurate within .002", clearly you have something wrong. Maybe you have the machine setup in metric not inches? Another recommendation: Most places do not recommend microstepping greater than 10x, I would set your machine to 8 instead of 16.

    Russ

  12. #12
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    Re: Chinese stepper motors, how many steps?

    I should have mentioned...I DO have Mach 3 set up for metric, it makes more sense to me. (Until I have to do all these conversions, of course!) So the 640 steps figure lines up with the 16256 figure (16256/25.4 = 640). But still, 640 is significantly different from the 500 steps per unit, which seems to be pretty accurate.

    I'll look into changing the 16 to 8. I built the drivers from a kit and the guy helped me set up the micro stepping but I don't remember why he set z to 16. Out of curiosity, what is the advantage of 8 vs. 16?

  13. #13
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    Re: Chinese stepper motors, how many steps?

    On micro steps on a stepper motor these are not exact steps, but they have determined that if you apply the right voltage for the right amount of time the motor moves a predictable amount between the two of the 200 poles on a typical stepper motor. The greater the microstep number, you can increase your resolution. If you ask the expects from Gecko drive for example they will tell you after 10 there is no gain and it actually gets worse, that is why I recommend 8. When you have it set to 8x and 200 p/r then you get 1600 pulses per revolution which is similar to many servo motors, so you have higher resolution. While 16 might look good on paper because you double the resolution it is really not recommended, you will find 8x will work just fine and give you good results.

    Do you have backlash in your system, since this was a Chinese machine they are probably using ballscrews so backlash would be minimum and certainly not enough to throw off your calculations that much.

    Here is what I would recommend. Do some tests... Put a piece of tape on the ballscrew of any given axis and using a fine tip marker to draw a line. Then get a piece of wire or something that can point to the line. Now issue 200 pulses and see if the motor actually turns exactly one time. Do this test on all axis.

    Off the top of my head the most logical reason you are off is something is set wrong on the stepper driver board. But start with the test I just suggested. You must have the motor driver with microstepping turned off for that test. Then do the test again with 4X microstepping. It should take 800 pulses to turn one revolution, and step your way up and see if something is set wrong.

    My guess is the motor will turn exactly one turn when set to no microstepping, but you need that data point first so you can figure out exactly what is happening.

    Russ

  14. #14
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    Re: Chinese stepper motors, how many steps?

    If your numbers don't match, there has to be an error somewhere. It's math, not magic. Could it be that your microstepping is set to 1:5 instead of 1:16? That would be a perfect match: 200 steps per turn * 5 microsteps / 2mm pitch = 500 steps per mm. (Yes, there are stepper drivers that do decimal microstepping - 1:5, 1:10, 1:25 and so on.)

  15. #15
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    Re: Chinese stepper motors, how many steps?

    These are the drivers I'm using:

    6064: 4AMP Stepper Motor Driver Kit. massmind

    As far as I can tell, 5 micro steps isn't an option. I also don't know what the pitch really is, since it appears the standard for these machines is 5mm. I'll take the nut off and run over to Home Depot to check.

    CNCMAN172, I'll run your test in a little bit. It doesn't look like I have much backlash, though I haven't tested for it other than watching the dial at the end of a movement. For the test though, could I put tape on the hand wheel of the motor and the motor assembly, draw two lines to show the point of origin and run the test? That way if they line back up after 200 pulses, the motor would have made one revolution. Right?

    Also when I remove the jumpers for micro stepping, the 200 pulses would be the same as 200 steps/unit in mach 3?

    EDIT: OK it looks like I can't even set the driver board to no micro steps. If I don't use any jumpers I have 64 micro steps. The closest I can get is 2.

  16. #16
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    Re: Chinese stepper motors, how many steps?

    Canman77,

    This driver seems to have these options for steps but did not see the manual to make sure you have it set correctly.

    Yes, you can put the tape anywhere as long as you can tell the motor actually rotates one rotation during that test.



    Selectable phase drive (1/2,1/8,1/10, 1/16, 1/20, 1/32, 1/40, 1/64 step)


    Russ

  17. #17
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    Re: Chinese stepper motors, how many steps?

    Canman77,
    Missed this question.

    Also when I remove the jumpers for micro stepping, the 200 pulses would be the same as 200 steps/unit in mach 3?

    No... You will need to tell MACH3 the steps per unit are 200 * ballscrew calculation, depending on if you have a 5MM or 10MM ballscrew. Then tell MACH3 to go from 0 to 1", the shaft should rotate one time.

    Russ

  18. #18
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    Re: Chinese stepper motors, how many steps?

    The manual is mainly a guide for building the driver, not so much for fine tuning it. But step 15 below and the chart to the right are somewhat helpful:

    Slowing 69.16.243.61&c=1&t=42690.4470497685

    I think the idea behind this driver is to tweak it until you find a setting that works for the machine. So I'll probably have to start with 1/2 stepping and see. I'm going to go dig into the drivers and run the test. I'll let you know what I find. Thanks for all the help, I appreciate it.

    EDIT: Also thanks for the Mach3 explanation for the test, I'll start with a 5mm pitch.

  19. #19
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    Re: Chinese stepper motors, how many steps?

    Quote Originally Posted by canman77 View Post
    Also when I remove the jumpers for micro stepping, the 200 pulses would be the same as 200 steps/unit in mach 3?
    Only if you have a drive screw with a 1mm pitch. With a 2mm pitch screw the number would be 200/2=100 steps/unit, with a 5mm pitch the number would be 200/5=40 steps per unit and so on.

    Here is a crazy thought: check if you have scaling turned on in Mach3. Did you install Mach3 yourself, or did it come with the machine?

  20. #20
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    Re: Chinese stepper motors, how many steps?

    Quote Originally Posted by CitizenOfDreams View Post
    Only if you have a drive screw with a 1mm pitch. With a 2mm pitch screw the number would be 200/2=100 steps/unit, with a 5mm pitch the number would be 200/5=40 steps per unit and so on.

    Here is a crazy thought: check if you have scaling turned on in Mach3. Did you install Mach3 yourself, or did it come with the machine?
    I installed Mach 3 myself...so I have no idea if I have scaling turned on! I'll take a look. What does scaling do, and should it or should it not be on?

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