Problem: Losing Steps?


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Thread: Problem: Losing Steps?

  1. #1

    Default Problem: Losing Steps?

    Hello, I've been having an issue with my converted cnc milling machine that seems to be progressively getting worse. It seems to be losing steps of sorts on the X axis only.

    The machine uses Pacific Scientific Stepper Drivers and Powermax II stepper motors (P22NRFB-LNN-NS-00).

    I've narrowed it down to being a motor issue. I've picked up 0,0,0 and ran a program without cutting any metal and the error on the x was approximately 0.9mm.

    The second time I repeated the same process and had 0.5mm of error on the x axis.

    I believe that this isn't a controller offset issue as I ran the identical program both times from the same position. The x axis everything is moving freely, I just disassembled it to verify and everything is nice and smooth.

    Sitting idle (no motion commanded, machine on to pump way lube only), the stepper motor for the X axis is much warmer (about 85 degrees F vs the Y axis at 75 degrees)

    I'm looking for opinions, could my issue be the motor? Could it be the driver?

    Thanks
    Jeremy

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  2. #2
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    Quote Originally Posted by Chattygt View Post
    The machine uses Pacific Scientific Stepper Drivers and Powermax II stepper motors (P22NRFB-LNN-NS-00).
    Jeremy
    Not enough info. What size Mill?. What voltage are you running drivers from?. What amp setting?. Motors wired in seris/ bi/ or parallel config.

    Anything less than 48v on a nema23, generally crap, torque drop is huge.
    If machine is G0704 size, your motors are too small.
    Motors wired in parallel give most balanced performance.



  3. #3

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    Quote Originally Posted by dazp1976 View Post
    Not enough info. What size Mill?. What voltage are you running drivers from?. What amp setting?. Motors wired in seris/ bi/ or parallel config.

    Anything less than 48v on a nema23, generally crap, torque drop is huge.
    If machine is G0704 size, your motors are too small.
    Motors wired in parallel give most balanced performance.


    Alright. Going to try my best to answer. It's a dyna myte 1007 10 inches x 7 inches travel.

    I'm unsure how to find the rest of that info. They're 8 wire and it's wired in pairs of 2 tied together. 4 connections, 2 wires in each.

    Factory steppers only supplied 27 ounce inches of torque from the literature I could find.



  4. #4

    Default Re: Problem: Losing Steps?

    I've attached some photos.

    I'll check voltage at the driver tonight when I head out to the shop.

    Attached Thumbnails Attached Thumbnails Problem: Losing Steps?-20211118_231148-jpg   Problem: Losing Steps?-20211118_231137-jpg   Problem: Losing Steps?-received_528671981846627-jpg   Problem: Losing Steps?-screenshot_20220128-163624_chrome-jpg  



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    Default Re: Problem: Losing Steps?

    Hi,
    Pacific Scientific make great quality motors.....but there seems to be a discrepency between two of your photos.

    One shows the name plate of the motor which shows power of 71W whereas the table shows the axis motors having a power of 230W?? Maybe they are referring to the
    combined power of the three motors??

    Either way I would be guided by the motor nameplate. Having said that the nameplate says 1500rpm, which is very fast for a stepper, so maybe the Yanks have come up with
    a BS number, they are not above BS!

    The eight wires mean that the windings are arranged in two phases with two coils in each phase, ergo eight wires. This arrangement allows you tow wire them in bipolar series,
    bipolar parallel or bipolar centre tapped. This arrangement allows the greatest flexibility and is favored by manufacturers.

    In order to get the best possible torque and best possible speed you must wire your motors in bipolar parallel. Can you find any more info about the motors, particularly the
    wire colour assignment.....that would be easiest, you can measure it and do it empirically but it would be hard to step you through it over the internet unless you are already familiar
    with the process and have the gear, a signal generator and an oscilloscope?.

    If you can confirm that the motors are wired in bipolar parallel then you have the max the motors can produce. If there is no mechanical or an issue with the drivers then you'd need
    to replace the steppers with more powerful units. If however they are NOT wired in bipolar parallel but say bipolar series, then correcting that will increase the torque and speed by
    a factor of four. Would that be enough?

    Craig



  6. #6

    Default Re: Problem: Losing Steps?

    Thanks for the description. Maybe my issue is this axis is wired differently, hence the issue on one axis.

    I'll dig around and verify a few things you all have suggested, driver voltage and the proper wiring diagram.

    Thank you.

    Also to elaborate, I may have made things confusing. The spec sheet is the original specs of the machine, it was converted to these steppers and drivers before I purchased it.



  7. #7

    Default Re: Problem: Losing Steps?

    Based on this diagram, the motor is wired in bipolar parallel. I'll verify the drive voltage when I can tonight.

    I really appreciate the quick responses. This machine is a work horse for me when I receive orders. I don't want to keep it down for too long.

    Also with regards to the 1500 rpm. I've wondered if perhaps I'm over spinning them. As there is a belt driven reduction built into the machine. The ball screw has a larger pulley than the motor.

    I've lowered my acceleration and deceleration settings but that hasn't seemed to help. Unless maybe I didn't go low enough.

    Attached Thumbnails Attached Thumbnails Problem: Losing Steps?-screenshot_20220128-182951_acrobat-samsung-jpg  


  8. #8

    Default Re: Problem: Losing Steps?

    Confirming I have 51.5V at the stepper driver, even while Y axis is homing. I'm unable to verify at a higher speed. Could that be a potential issue ?

    Edited: had someone hold the y axis button, when the axis is moving at full speed voltage drops to 50.5v.

    Maybe I should try reconnecting x axis and verifying voltage while it's moving ?

    Drivers are pacific scientific 6410.

    Last edited by Chattygt; 01-28-2022 at 09:29 PM.


  9. #9

    Default

    Quote Originally Posted by Chattygt View Post
    Confirming I have 51.5V at the stepper driver, even while Y axis is homing. I'm unable to verify at a higher speed. Could that be a potential issue ?

    Edited: had someone hold the y axis button, when the axis is moving at full speed voltage drops to 50.5v.

    Maybe I should try reconnecting x axis and verifying voltage while it's moving ?

    Drivers are pacific scientific 6410.


    Another thing to add. Doing research I realized that the specs for this machine were using the original dc servo axis drives.

    I may be over spinning the axis motors when utilizing rapid motion. Going to reassemble and test this theory. I was rapiding at 5000 mm/min, which I thought was typical. I may reduce to 2500 and report back.

    Edited:
    After calculating, the motor has an 18 tooth pulley, ball screw is 36 tooth. Motor max rpm is 1500. I was significantly over spinning (or at least attempting to over spin the motor). I will reduce my rapids and report back.



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    Default Re: Problem: Losing Steps?

    Hi,

    had someone hold the y axis button, when the axis is moving at full speed voltage drops to 50.5v.
    That voltage drop is inconsequential. By all means hook up the X axis and compare.

    A 50V power supply surprises me, its lower, quite a bit lower than I would have expected. With the '1500rpm' on the label I would have expected the voltage to be north of 100VDC.
    Good low inductance steppers (less than 1.5mH) could be expected to retain 35% of the holding torque at 1000rpm with a 60-80VDC driver. A lesser motor, say 4mH inductance,
    would be lucky to have 25% of its holding torque at 500 rpm, let alone 1000 rpm, and at 1000rpm I would expect less than 10%.

    Taking the two considerations in mind, ie high voltage equates to high speed and low inductance equates to highspeed leaves a bit confused about what steppers you have,
    are they some 'super low inductance whizz bangs that defy physics' or what?????

    I suspect you are right, this machine was equipped with servos and clearly steppers are never going to match them no matter how hard you try.

    What I would recommend is calculate the gear reduction ans set the max velocity such that the stepper is doing 500rpm at max velocity. Set the acceleration to 10% of that.
    Then, leaving acceleration alone, increase the max velocity until it stalls or starts missing steps. That is a better and more practical measure of what your steppers can achieve in your machine.
    Once you have established that limit, reduce the max velocity to 75% of what you have found and start increasing the acceleration, until it too starts missing/stalling.
    The aim is to have as high acceleration as possible, it promotes the best and fastest toolpath following, and is usually more important to cycle time than max velocity, strange as it
    may sound. Most toolpaths spend more time accelerating than at max velocity, so acceleration is favoured over max velocity.

    Craig



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    Default Re: Problem: Losing Steps?

    Hi,

    Motor max rpm is 1500.
    Dubious, especially with only 50VDC to urge them along, if you had 150VDC to push them then yes I would say 1500rpm sounds possible.

    Craig



  12. #12

    Default

    Quote Originally Posted by joeavaerage View Post
    Hi,



    That voltage drop is inconsequential. By all means hook up the X axis and compare.

    A 50V power supply surprises me, its lower, quite a bit lower than I would have expected. With the '1500rpm' on the label I would have expected the voltage to be north of 100VDC.
    Good low inductance steppers (less than 1.5mH) could be expected to retain 35% of the holding torque at 1000rpm with a 60-80VDC driver. A lesser motor, say 4mH inductance,
    would be lucky to have 25% of its holding torque at 500 rpm, let alone 1000 rpm, and at 1000rpm I would expect less than 10%.

    Taking the two considerations in mind, ie high voltage equates to high speed and low inductance equates to highspeed leaves a bit confused about what steppers you have,
    are they some 'super low inductance whizz bangs that defy physics' or what?????

    I suspect you are right, this machine was equipped with servos and clearly steppers are never going to match them no matter how hard you try.

    What I would recommend is calculate the gear reduction ans set the max velocity such that the stepper is doing 500rpm at max velocity. Set the acceleration to 10% of that.
    Then, leaving acceleration alone, increase the max velocity until it stalls or starts missing steps. That is a better and more practical measure of what your steppers can achieve in your machine.
    Once you have established that limit, reduce the max velocity to 75% of what you have found and start increasing the acceleration, until it too starts missing/stalling.
    The aim is to have as high acceleration as possible, it promotes the best and fastest toolpath following, and is usually more important to cycle time than max velocity, strange as it
    may sound. Most toolpaths spend more time accelerating than at max velocity, so acceleration is favoured over max velocity.

    Craig
    Thank you very much. I'll definitely take that advice. The ball screw is half the speed of the motor, with a 2.5mm pitch.

    From reading the pacific scientific literature the voltage for these drivers is 25-75VDC, same literature for motors shows torque charts with a max of 3k rpm.

    Thank you all for your help. I was really starting to worry I would be replacing motors or drivers.

    I'll reduce rapid and acceleration and go from there.



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    Default Re: Problem: Losing Steps?

    Hi,
    From reading the pacific scientific literature the voltage for these drivers is 25-75VDC, same literature for motors shows torque charts with a max of 3k rpm.
    I've just been reading/digesting the charts you have posted and your stepper P22NRFB-LNN-NS-00 has a torque of only 70oz.in at 5000 full steps/sec, ie 1500rpm, and
    less than 40oz.in at 10000 full steps/sec. You steppers will miss steps or stall LONG before you get to those speeds.

    Voltage applied to a stepper is about the driver, not the stepper.

    I used 5 phase Vexta steppers on my previous mini-mill and matching Vexta drivers, and they applied over 150VDC and I ran them for years at 2400rpm,
    and could tune then as high as 3000rpm, if somewhat less reliably. If you want steppers to go fast apply the highest voltage driver you can find.

    If you want to go faster than that get AC servos. I use 750W Delta AC servos on my new mill, direct driving 5mm pitch screws to 5000rpm for 25m/min rapids. Its
    scary fast, so I've deliberately detuned then to 15m/min. This machine weighs 800kg, so when it accelerates you bloody well know about it! Servos eat steppers
    for breakfast.....I'll never go back to them.

    Craig



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    Default

    Quote Originally Posted by Chattygt View Post
    Another thing to add. Doing research I realized that the specs for this machine were using the original dc servo axis drives.

    I may be over spinning the axis motors when utilizing rapid motion. Going to reassemble and test this theory. I was rapiding at 5000 mm/min, which I thought was typical. I may reduce to 2500 and report back.

    Edited:
    After calculating, the motor has an 18 tooth pulley, ball screw is 36 tooth. Motor max rpm is 1500. I was significantly over spinning (or at least attempting to over spin the motor). I will reduce my rapids and report back.
    How has this thing been reliable so far trying to get 5000mm/min from it?!.
    I'll be surprised if it's reliable at 2500mm to be fair.
    Those drivers are stupidly expensive. Look to be max 75vdc so 50v should be fine. However, even I had to go to 60vdc just to get my mill steppers above 3000mm direct screw connected.
    YOU SHOULD HAVE SERVOS ON THIS!. Simple as that.
    Whoever changed to a stepper system made the big mistake.

    Next time I'll give steppers a miss and go to servos as well.



  15. #15

    Default

    Quote Originally Posted by dazp1976 View Post
    How has this thing been reliable so far trying to get 5000mm/min from it?!.
    I'll be surprised if it's reliable at 2500mm to be fair.
    Those drivers are stupidly expensive. Look to be max 75vdc so 50v should be fine. However, even I had to go to 60vdc just to get my mill steppers above 3000mm direct screw connected.
    YOU SHOULD HAVE SERVOS ON THIS!. Simple as that.
    Whoever changed to a stepper system made the big mistake.

    Next time I'll give steppers a miss and go to servos as well.

    Oh wow. This is somewhat disappointing but good to know. I'll start looking into what can be done to convert it to servo drives. My controller doesn't have a spot for position feedback, just a step/drive provisions.

    I'm somewhat familiar with supervexta drivers. The lathe I'm currently converting uses them with older steppers.

    I'll have to weigh my options and see what can be done. The delta set up would be a little pricey, but if that's what i should go with I'll work towards that.

    Any suggestions servo/driver wise (I understand wrong forum, but looking for suggestions from those that have replied) ?



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    Quote Originally Posted by Chattygt View Post
    Oh wow. This is somewhat disappointing but good to know. I'll start looking into what can be done to convert it to servo drives. My controller doesn't have a spot for position feedback, just a step/drive provisions.

    I'm somewhat familiar with supervexta drivers. The lathe I'm currently converting uses them with older steppers.

    I'll have to weigh my options and see what can be done. The delta set up would be a little pricey, but if that's what i should go with I'll work towards that.

    Any suggestions servo/driver wise (I understand wrong forum, but looking for suggestions from those that have replied) ?
    There's always a way.
    Do you have a link to your machines manual?.
    I had a look at one but not sure if it's the right one.
    Noticed 6x 8 pin encoder headers and 6x headers for axis control.
    Sounds perfect for servo drives but, does that sound like what's on your controller?.

    This is the one I looked at:
    https://www.google.com/url?sa=t&source=web&rct=j&url=https://transistor-man.com/files/miters_mill/DYNA_4M_OPERATION_REFERENCE_OCR.pdf&ved=2ahUKEwjN7 KL_itf1AhVGasAKHewVCX8QFnoECAMQAQ&usg=AOvVaw2uUOMx BZx_NZh0yxbGsjtp

    Controller board image page 37.
    When it comes to servos just look for something 400w with 17bit encoders (delta are 160,000 count).
    Your machine showed 0.23kw so the above spec should be plenty.

    I reckon Craig would have a clue on the wiring up.
    If you ever decide to go that route.

    If copying the link don't work then google:
    dyna myte 1007 controller manual
    It came up as top result as a pdf



  17. #17

    Default

    Quote Originally Posted by dazp1976 View Post
    There's always a way.
    Do you have a link to your machines manual?.
    I had a look at one but not sure if it's the right one.
    Noticed 6x 8 pin encoder headers and 6x headers for axis control.
    Sounds perfect for servo drives but, does that sound like what's on your controller?.

    This is the one I looked at:
    https://www.google.com/url?sa=t&source=web&rct=j&url=https://transistor-man.com/files/miters_mill/DYNA_4M_OPERATION_REFERENCE_OCR.pdf&ved=2ahUKEwjN7 KL_itf1AhVGasAKHewVCX8QFnoECAMQAQ&usg=AOvVaw2uUOMx BZx_NZh0yxbGsjtp

    Controller board image page 37.
    When it comes to servos just look for something 400w with 17bit encoders (delta are 160,000 count).
    Your machine showed 0.23kw so the above spec should be plenty.

    I reckon Craig would have a clue on the wiring up.
    If you ever decide to go that route.

    If copying the link don't work then google:
    dyna myte 1007 controller manual
    It came up as top result as a pdf

    The machine never came with a controller and I retrofitted the machine with a digital dream ddcsv3.1. If the ac servo driver accepts a step and dir signal it should work no issues.

    Now for the dreaded ac vs dc servo research ????



  18. #18
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    Default

    Quote Originally Posted by Chattygt View Post
    The machine never came with a controller and I retrofitted the machine with a digital dream ddcsv3.1. If the ac servo driver accepts a step and dir signal it should work no issues.
    Shouldn't be a problem. The ddcv is very limited though.
    I think I would go the AC servo route myself.
    I would then get a multi channel isolator board to match my input / output voltages, tie the servo fault outputs together on there. Then attach that board to the e-stop input circuit. So then if a servo faults it will estop it.
    Pity about no encoder feedback option.

    I get most of my stuff on Aliexpress these days.



  19. #19

    Default

    Quote Originally Posted by dazp1976 View Post
    Shouldn't be a problem. The ddcv is very limited though.
    I think I would go the AC servo route myself.
    I would then get a multi channel isolator board to match my input / output voltages, tie the servo fault outputs together on there. Then attach that board to the e-stop input circuit. So then if a servo faults it will estop it.
    Pity about no encoder feedback option.

    I get most of my stuff on Aliexpress these days.


    Awesome! I'll look into that route. Appreciate it!



  20. #20
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    Default Re: Problem: Losing Steps?

    Hi,
    if you are interested in servos look into Delta (Taiwanese made in China) and DMM (Canadian made in China). They are both good quality
    with high resolution encoders, good backup, good documentation and most importantly free set-up and tuning software at very fair prices.

    There are many hundreds of parameters that need to be programmed into a modern servo drive. If you try to program them by pushing buttons like a
    microwave, you'll be there forever and STILL make a mistake.

    https://www.fasttobuy.com/Supply-asdab2-series_c498

    There are even cheaper Chinese made brands, Liuchan and ToAuto, come to mind. they are very well priced and attractive as a result, but the documentation is poor
    and no set-up and tuning software. I have no reason to doubt their quality or performance, its just hard to set them up, especially if this is your first foray into servos.

    Modern AC servos from all manufacturers tend to be very similar in terms of features and programming. If you've done one you've done them all. Delta and DMM
    are typically 25% more than Liuchan and ToAuto and well worth the extra.

    Many servo-newcomers favor Clearpath servos, and they are very good quality and industry leading after sales support but they are expensive for what you get.
    Firstly Clearpaths have as standard a paltry 800 count/rev encoder, one, only one, digital output, no auxiliary outputs and no analog inputs.
    A 400 W (actually 397W) Clearpath servo is $517USD while I paid $435 for a Delta B2 servo (160,000 count/rev)...that's twice the power for less.

    Craig



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Problem: Losing Steps?

Problem: Losing Steps?