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Stepper motors won't turn

Discussion in 'Tutorials' started by Alex Chambers, Mar 21, 2020.

  1. Alex Chambers

    Alex Chambers Master
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    A common request for help starts "My steppers make a noise, but don't turn"

    Those symptoms are exactly what you would expect if the motors are wired incorrectly.

    Openbuilds have stepper motors made to their specification, so our motors match our latest wiring diagrams (OpenBuilds BlackBox 4X Documentation).

    If you got your steppers from somewhere else, or have had them for some time you need to know that the colour coding of the wires on stepper motors are not standardised.

    Electrically, bi-polar stepper motors used for hobby cnc machines have two coils of wire - you need to find the pairs of wires connected to each coil.

    Disconnect the motors and check with a multimeter on continuity or resistance to find out which pairs of wires are connected to a coil (low resistance or continuity beep) .

    Treat one pair as A+ and A- and the other as B+ and B-.

    To make life easier disconnect the motor you are testing from the drive pulley or leadscrew and check to see which way it turns. If it turns the wrong way reverse A+/A- OR B+/B- and it should turn the right way.

    Come back to us if that doesn't solve the problem.
     
    #1 Alex Chambers, Mar 21, 2020
    Last edited: Mar 21, 2020
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  2. jeffmorris

    jeffmorris Well-Known
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    There is another way of finding pairs of wires: touch a pair of wires and try to turn the motor shaft. If the shaft won't turn, you found one pair and two other wires are another pair. Try to find data sheets for the motors as they tell you the colors of wires.
     
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  3. Alex Chambers

    Alex Chambers Master
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    Another common problem is "my steppers keep reversing direction, or just sit there making a noise"

    This is almost certainly (99.5% sure) one of the four wires making a poor connection.

    Check the wiring to the suspect stepper at all connection points - things to look for;
    Screw connectors not tight
    Gripping insulation instead of bare wire
    Poor crimp connectors (or even broken crimp inside the housing)
    Wire broken inside the insulation
    Connectors not pressed fully home

    Alex.
     
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  4. ulav8r

    ulav8r New
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    I will check continuity on the cables. Did not really suspect the motor because I was able move it several times before I started having issues.
     
  5. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
    Staff Member Moderator Project Maker Builder Resident Builder

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    Someone here (can't find the post now to give credit) has the brilliant saying "Wiring is always fine until it isnt anymore"! Its true though, connections wiggle loose, get knocked out and unplug, or break under all the back and forth. Especially on lesser machines with incorrectly spec'ed aluminum wiring, etc
     
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  6. ulav8r

    ulav8r New
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    Got it back out and checked continuity on the x-axis cable and it was good. I then pulled out another motor, hooked it up to the second controller and it worked ok. Disconnected from the second motor and hooked up the original motor. It worked ok so I ran one of the included programs. It ran to completion. I then hooked the original control board up and ran the program again.

    Apparently, the x-axis cable had come loose on one end or the other.

    Thanks for the help, I had no idea on what to look for based on the problem I had. This machine is much different from the commercial lathes and machining centers I worked with on the job.
     
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  7. ulav8r

    ulav8r New
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    A little more about my experience with the seller. When originally ordered I was give a leadtime of about 4 weeks. I received it in about 2 1/2 weeks. One I got it assembled there was an issue with the x-axis motor and coupler. The coupler wobbled and the motor shaft had about .001 runout. I emailed the seller and had a reply within 30 minutes. They agreed to provide replacements. The next day they emailed again, asking if it would be ok to send a complete machine that had been returned and I said ok to that. After about a week I got an email that the machine was not back yet. It ended up taking about 2 weeks total to get the replacement machine. Changing the motor and coupler fixed the original problem.

    When I opened the replacement, it showed signs of having been unpacked, but not of having been assembled. The laser in that machine was was a 3 watt whereas the one I bought originally was a 5.5 watt. To purchase another motor and coupler I will be able to setup a machine with the laser and not have to change out the spindle and laser to switch back and forth.
     

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