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Thread: A Axis setup

  1. #1
    looking for some ideas on the strange behaviour of my A axis setup
    I've justed added the driver, a DM542A from Longs motors
    Set up Linuxcnc and mapped a couple of spare output pins on parport 0 to the Step and Dir on the stepper driver
    Also added a 5volt feed to the stepper driver

    The green LED is lit and the red LED is not lit

    I can jog the A axis through gmoccapy, but its anything but smooth and its faster moving in one direction than it is in the other
    I did a quick and dirty test and it appears that one rev of the motor clockwise is 50 units on the display, but 25 units the other way completes the 1 rev anti clockwise

    Does it matter that the 5 volts is not from the BOB, its 4.6 volts, so I though this would be fine, but can run a wire from the BOB to the stepper driver.

    I may well have something wrong in Linuxcnc, but why would it jog 2x as far in one direction than it does in the other

    Any help much appreciated


  2. #2
    What's the 5V feed to the stepper driver? - sorry, don't understand that. I'm assuming that you're using the BoB to switch the "-" inputs to the driver with a common 5V supply to the "+" - in which case, so long as the 5V supply has a common earth with the BoB it'll be fine.

    Faster in one direction than another?, strange - step/dir means that the step generation is independent from the direction signal.

    Random thoughts - what's the frequency of the thread that your parport is driven by? (I'm doubting that Linuxcnc will stretch any performance requirements of the driver). here's a thought - slave the step input to your A-Axis to another known axis and confirm the behaviour (different rates/direction) - that'd tell us there's something amiss with the driver.

  3. #3
    I finally got bacck to this today, because my A axis arrived, UPS lost the first one, God knows how you loose a 7.2Kg parcel
    I replaced the 5 volt feed to the stepper driver with one from the BOB and all works perfectly now.
    I also installed a push on push off switch to the power feed on the driver so that it can be turned off when not using the A axis


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