Question about stepper motors

Discussion in 'The Projects Forum' started by jchal3, Feb 6, 2012.

  1. jchal3

    Thread Starter Member

    Dec 13, 2009
    78
    0
    Hello,

    I have a homemade cnc router. It has three pacific scientific stepper motors and drivers. The problem I am running into is as follows. As the machine runs a program the motors will lockup and start humming. It usually happens just as the z axis stops its movement and the x and y axis start to move. Has anyone had this trouble before or know what could cause it?

    Thanks for the help
     
  2. CVMichael

    Senior Member

    Aug 3, 2007
    416
    17
    Stepper motors have much more power at lower speed, so you have to always start the motor at low speed, then increase the speed
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,446
    3,362
    If possible try slowing down the motor or increase the supply voltage to the motor.
     
  4. stirling

    Member

    Mar 11, 2010
    52
    2
    what are the specs for your motors? phase current/phase inductance? 4,6 or 8 wire?
    what are the specs of your drivers? unipolar/bipolar - current selection/max voltage/microstepping?
    what are the specs of your power supply? current/voltage?
    what are you driving your system with? Mach3/EMC/other?
    what drive ratio? 1 rev of the motor moves the axis (X,Y and Z) how many inches/mm?
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    in addition to stirlings excellent questions...
    Did this just start happening? or has it always been like that.
    Stepper motors will lock/hum/hiss when powered on/just sitting there and not being driven by a step/direction signal. So this could just be normal and you just weren't expecting it.
    Do your drivers have an idle current reduction mode?
     
  6. jchal3

    Thread Starter Member

    Dec 13, 2009
    78
    0

    Stirling,
    Thanks for the reply. I will do the best I can to answer your questions. First the motors are pacific scientific powerpac motors. they are 1.8 degree step motors. 7.5 amp bipolar series, that run at 65 vdc. Po:( whatever that is) is 337watts. and they spin at 1350 rpm. All three motors are the exact same.

    second, the drivers are pacific scientific 5410 drivers. They run on 12-75vdc with 5 vdc logic. The are set to microstep at 25:1

    Third,

    My power supply is a 36v 4.2amp 150watt power supply. It is 110v input and I believe it is regulated.

    Fourth,

    I am driving my system using Mach 3

    Fifth

    the motors are direct drive to acme thread, so it is 6 rotations per inch. All three axis are the same.


    Note:
    When building this machine I was lead to belive that running this power supply would work as long it is was at "lowish" speeds. I have had the problem at speeds as low as 200mm per minute. If it has to be slower than that, then I need to change the power supply, because that is painful to watch.
     
  7. jchal3

    Thread Starter Member

    Dec 13, 2009
    78
    0

    Mcgyvr,

    This is something that seems to come and go. It will run fine for a while, and then all of a sudden it will happen with everything I run. It is hit or miss. Those are the hardest to solve.

    The drivers do have a current reduction mode, and it is switched on.
     
  8. jchal3

    Thread Starter Member

    Dec 13, 2009
    78
    0
    thanks for the help guys.
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Your motors drivers and PSU sound pretty good.

    I would look for a problem with the PC, especially as the stall issue "comes and goes".

    Some PC operating systems are terrible for making delays (windows interrupts etc that might take 0.1 seconds or more) and if a delay happens in the critical part of a acceleration ramp the motor can stall.

    Check with the suppliers of your PC software about the requirements on your PC. Often is is better to run a stripped down PC with no other software installed and lots of options turned off. Things like anitvirus are known to be bad for causing delays.
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
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    Yep windows sucks for accurate timing/latency when AV/networking,etc.. is turned on..
    Not to mention 25x microstepping.. Do you need that much? I'm not in the mood for the math but I'm sure that's way more resolution than you need but I bet the motion is really smooth..
     
  11. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,015
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    Is your power supply a switch mode or linear? Pac-sci in the 5410 manual says NOT to use a switch mode supply for their controllers.
     
  12. jchal3

    Thread Starter Member

    Dec 13, 2009
    78
    0
    Well I am running windows xp. That could be part of the problem. I'll look into it. Have you guys heard of resonance? Do you think that could be causing the stalls? How do you fix?
     
  13. jchal3

    Thread Starter Member

    Dec 13, 2009
    78
    0
    Well I am running windows xp. That could be part of the problem. I'll look into it. Have you guys heard of resonance? Do you think that could be causing the stalls? How do you fix?
     
  14. stirling

    Member

    Mar 11, 2010
    52
    2
    jchal3 - without data sheets it's all a bit guesswork unfortunately.

    I'm guessing someone has told you the 65V figure as this is not an unusual ballpark for DRIVING steppers but without knowing the phase inductance we can't deduce the *optimum* drive voltage so we'll go with 65V at the moment. Now let's look at your 7.5A/phase (serial).

    Assuming you actually have your motors wired serial this means your power supply will need to be capable of delivering approx. 15A for your 3 motors (assuming your drivers are choppers).

    You can see you're seriously lacking in both V and A. Your 36V will roughly HALF your motors potential speed and your power supply current capability is way down the scale and will result in a serious loss of potential torque. Note: ideally you should be using an UN-regulated supply as regulated and switch-mode are not the first choice for driving steppers but as I've said you're so mis-matched VA-wise, this is not your main problem.

    Just as an aside you said "they spin at 1350 rpm". I'd be absolutely amazed if this is true with your setup as you've described it - or do you mean someone told you this? That would give you a rapid rate of getting on for 6 meters a minute and I'm guessing you wouldn't have posted your question. But note that this is nowhere near an unreasonable goal with a correctly matched system.

    Moving on to your controller. Mach3 under XP happily runs professional machines all over the world so I doubt very much that your Mach3/OS/hardware mix is an issue though you could be unlucky (But note: don't even think of running a network on the same machine). You can soon test the quality of your step pulse stream by running Mach3's driver test (in your Mach3 install folder). But generally if you need to check out your Mach3 setup like motor tuning (accel/max vel) settings etc. then I'd suggest you meet us over on the Mach3 forum.

    Just a couple of other points. Personally I'd turn OFF your current reduction. This known to cause problems with steppers when first starting a move. Also drop your microstepping to as near 10 as you can - anything else is "empty resolution".

    Finally - resonance - I'd forget this at the moment. From what you said in your OP it's not likely to be your main concern. I doubt your motors are even approaching the speed where resonance would rear its ugly head. Plus with quality microstepping drives its unlikely anyway.

    Like I said at the beginning without data sheets I can only guess but it looks like from what you've said that you're system is just mis-matched and seriously under powered.
     
    shortbus likes this.
  15. jchal3

    Thread Starter Member

    Dec 13, 2009
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    thanks Stirling,

    It is clear that I probably need to look for a new power supply. Any ideas on where to get a cheap one? And what would you suggest, most that I have found are 48v or 36v and the best I have found current wise is 10-15. Obviously an improvement, but if I'm buying one I might as well get the right thing.

    As for the 1350 rpm. That is only in my dreams. I run this thing at around 300mm per minute, and that seems to be too much already.

    My controller is Mach3, but it is on a lap top running Windows XP home. It does have a wireless card as well. Would this be causing a problem (note: Mach 3 driver test checks out fine)
     
  16. jchal3

    Thread Starter Member

    Dec 13, 2009
    78
    0
    Stirling,

    I forgot to add that the specs for the motor that I posted earlier came directly off of the motor plate. The stepper driver specs came out of memory, but from the manual. I didn't have it in front of me at the time. I will post the pdf of the manual this evening. Maybe that will help out.
     
  17. stirling

    Member

    Mar 11, 2010
    52
    2
    I can't make a suggestion without data sheets. If you can get those I'm happy to help.

    OOps - bad and bad!

    Notwithstanding your PS issues, Mach3 is NOT supported on laptops. See the Mach3 downloads page for the disclaimer and explanation. Any networking alongside Mach3 is a no no. Some have got away with it but lucky them.

    data sheets rule - motors/drivers/power supply - the more you can get hold of the better you'll be!
     
  18. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The Pac-Sci 5410 manual that I have shows a simple and easy power supply schematic in it. Just a transformer ,bridge rectifier and smoothing capacitor, gives the specs needed too IIRR. Can post the PDF if you can't find it.
     
  19. jchal3

    Thread Starter Member

    Dec 13, 2009
    78
    0
    shortbus,

    I think I may have been the one to give you the manual. I was looking at some posts from when started building this machine, and you weighed in on those conversations as well. Thanks for the help, and good hearing from you again.

    I am going to attach the manual here as well
     
  20. jchal3

    Thread Starter Member

    Dec 13, 2009
    78
    0
    I'll be honest. I think building the power supply might be a little over my head, but I think if I do a little you tube searching I might be able to get enough of an idea to pull it off.

    I started this whole project to learn a little bit, I just didn't think I would have to learn something new EVERY step of the way haha.
     
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