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IndustryArena Forum > OpenSource CNC Design Center > Arduino > homing x axis with two motors and drivers
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  1. #1
    Join Date
    Mar 2011
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    333

    homing x axis with two motors and drivers

    If you are using something like a G540 and MACH3 and you have an axis with 2 motors on it you can home each separately to maintain squareness of your gantry.
    How do you do that using GRBL and UGS?
    Thanks

  2. #2
    Join Date
    Mar 2015
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    409

    Re: homing x axis with two motors and drivers

    If you want to run 2 motors in sync, connect them to two separate drivers and feed that drivers with the same step/directory/enable signal. Once the motors are setup square, they will remain square.

    Alternatively connect the two spindles by one driving shaft , this is easy to do and works OK.

    If you really need to home the two spindle motors separately then each motor needs a driver that is controlled individually. I don't think it can be done using GRB!

  3. #3
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    Mar 2011
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    Re: homing x axis with two motors and drivers

    Quote Originally Posted by hfjbuis View Post
    If you want to run 2 motors in sync, connect them to two separate drivers and feed that drivers with the same step/directory/enable signal. Once the motors are setup square, they will remain square.

    Alternatively connect the two spindles by one driving shaft , this is easy to do and works OK.

    If you really need to home the two spindle motors separately then each motor needs a driver that is controlled individually. I don't think it can be done using GRB!
    Do you put limit switches on both motors or just one then?

  4. #4
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    Mar 2015
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    Re: homing x axis with two motors and drivers

    Do you put limit switches on both motors or just one then?
    You only need one limit switch because both motors should be in sync (after initial setup).

  5. #5
    Join Date
    Apr 2003
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    540

    Re: homing x axis with two motors and drivers

    You should be using the the slave axis settings in Mach. Each motor should have it's own driver. Connecting 2 motors to one axis/driver will work if you reverse the wiring on one, but it's not the best way and can cause other issues.

  6. #6
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    Mar 2011
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    Re: homing x axis with two motors and drivers

    Quote Originally Posted by coherent View Post
    You should be using the the slave axis settings in Mach. Each motor should have it's own driver. Connecting 2 motors to one axis/driver will work if you reverse the wiring on one, but it's not the best way and can cause other issues.
    Except that I am using an arduino and GRBL so there is no fourth axis support. I am driving the 2 motors with 2 drivers from one set of step/direction pins on the arduino.
    What "other issues" can it cause?
    Thanks

  7. #7
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    Apr 2003
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    540

    Re: homing x axis with two motors and drivers

    Quote Originally Posted by tkms002 View Post
    .
    What "other issues" can it cause?
    Thanks
    Instability, loss of torque (each motor would get roughly half the current that the driver would normally supply to one motor), possible timing issues. You are doubling the reactance or inductance applied to the driver. This will likely cause instability and loss of torque of the motors at higher drive frequencies resulting in lost steps. This is a nonlinear function, meaning torque drops more rapidly with increasing drive frequency. This will severely limit the maximum speed of your machine. In addition, the back EMF from two motors under certain operating conditions may add up to the point where it exceeds the voltage rating of the driver which can result in damage to the driver.

  8. #8
    Join Date
    Mar 2011
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    333

    Re: homing x axis with two motors and drivers

    Quote Originally Posted by coherent View Post
    Instability, loss of torque (each motor would get roughly half the current that the driver would normally supply to one motor), possible timing issues. You are doubling the reactance or inductance applied to the driver. This will likely cause instability and loss of torque of the motors at higher drive frequencies resulting in lost steps. This is a nonlinear function, meaning torque drops more rapidly with increasing drive frequency. This will severely limit the maximum speed of your machine. In addition, the back EMF from two motors under certain operating conditions may add up to the point where it exceeds the voltage rating of the driver which can result in damage to the driver.
    Except that I clearly stated that I am driving the two motors with two drivers.

  9. #9
    Join Date
    Mar 2015
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    409

    Re: homing x axis with two motors and drivers

    Instability, loss of torque (each motor would get roughly half the current that the driver would normally supply to one motor), possible timing issues. You are doubling the reactance or inductance applied to the driver. This will likely cause instability and loss of torque of the motors at higher drive frequencies resulting in lost steps. This is a nonlinear function, meaning torque drops more rapidly with increasing drive frequency. This will severely limit the maximum speed of your machine. In addition, the back EMF from two motors under certain operating conditions may add up to the point where it exceeds the voltage rating of the driver which can result in damage to the driver.
    These conditions can happen when you are running 2 motors attached to 1 driver and I agree that is not the way to do it.

    @tkms002 is running 2 motors attached to 2 drivers, so these conditions do not apply to his setup!

  10. #10
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    Re: homing x axis with two motors and drivers

    Quote Originally Posted by hfjbuis View Post
    These conditions can happen when you are running 2 motors attached to 1 driver and I agree that is not the way to do it.

    @tkms002 is running 2 motors attached to 2 drivers, so these conditions do not apply to his setup!
    Thank you
    Are there any other issues I may encounter?

  11. #11
    Join Date
    Jan 2005
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    1943

    Re: homing x axis with two motors and drivers

    for squaring a stepper driven system with 2 motors on one axis you can simply jog that axis to a set of hard stops, allowing one motor to stall and then the other. It is crude, but works very well. This is how I square the z-axis of my 3d printer. Once square then you can run the homing sequence and both motors will run and stay square.

  12. #12
    Join Date
    Jul 2006
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    1

    Re: homing x axis with two motors and drivers

    Quote Originally Posted by 109jb View Post
    for squaring a stepper driven system with 2 motors on one axis you can simply jog that axis to a set of hard stops, allowing one motor to stall and then the other. It is crude, but works very well. This is how I square the z-axis of my 3d printer. Once square then you can run the homing sequence and both motors will run and stay square.
    Two thumbs up for the best answer. All you need to remember to do is fabricate adjustable hard stops for each end.

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