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Trouble with motor smoothness!!

Discussion in 'General Talk' started by Travis Hamilton, Mar 23, 2017.

  1. Travis Hamilton

    Travis Hamilton Well-Known
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    I need some help I'm kind of stumped. I got my electronics all hooked up and working that was great seeing my plasma table move for the first time! But then i tryed to calibrate it which i got it moving the right distance and everything but the table will only move slow and vibrates and squeaks. But if i increase the stepps/mm it runs fine do i have to gear it down to increase stepps /mm? Or is there something i can do to fix it? Thanks
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    You'll need to be a little more specific as to your "electronics"...
     
  3. Travis Hamilton

    Travis Hamilton Well-Known
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    Ok sorry. So i have an arduino uno with v3 shield running 36v polulu drivers they are 85.... I don't remember the rest of the numbers and 425oz bipolar steppers they are 8 wire motors that are wired in parallel the power supply is 36v also running grbl panel. Hope this helps
     
  4. Travis Hamilton

    Travis Hamilton Well-Known
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    I should also note that i am running a chain drive and one full rev moves the gantry 140mm so i calculated and measured and came up with 2.856 steps/mm with shield set on half steps.
     
  5. Travis Hamilton

    Travis Hamilton Well-Known
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    So today i thought i would try the driver current i adjusted them according to the pololu video on they're site still not working. The only other thing i thought of is if i should wire the motors different? Instead of bipolar parallel? I am stumped as to way it runs better at higher steps/mm in the grbl settings. I don't want to gear it down unless i absolutely have too. Any input would be welcome. Thanks
     
  6. snokid

    snokid Master
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    ok lots to do....

    video of the machine moving.
    cut and paste your grbl settings.
    what do you had your feed speeds set at?

    from what you have said seems like current, but without more information hard to guess...
    Bob
     
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  7. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    DRV8825 drivers?

    They're not up to the task of big motors, especially rewired 8 wire motors (the conversion to bipolar, would obviously increase the resistance of the windings, now twice as long, further stressing the driver)
    They are only rated to around 1.8A with active cooling on those little breakout PCBs, max 2A on a big proper PCB (The TI ThermalPad package has a pad under the chip that uses the PCB asa a heatsink, so bigger is better)

    When you dont have enough current, you cant properly accelerate the motor, likely leading to stalling, which matches your description of the sounds.

    You may want to replace the DRV8825s with proper muscle like DQ542MA Stepper Motor Driver instead

    You would also have definate results with NEMA 23 Stepper Motor - High Torque Series or NEMA 23 Stepper Motor paired with to the DQ542MAs (; - its a well tested combination
     
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  8. Travis Hamilton

    Travis Hamilton Well-Known
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    20170324_131454.jpg 20170324_131430.jpg 20170324_132018.jpg 20170324_132043.jpg ok so here are some pics sorry about the screen pic of grbl settings i could not copy and paste anyway i think you can see them good enough there are 2 pics cause i had to scroll down. The other pics are the drivers and the chain drive set up. I am still working on the video it is a mp4 and not sure how to change that on my phone so i hope this helps oh and the motors almost spund like "the brakes are on" when the steps are set lower so i hope this helps
     

    Attached Files:

  9. Travis Hamilton

    Travis Hamilton Well-Known
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    I was wondering if this might be the problem thanks for the response i guess i will have look into some different drivers
     
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  10. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Thanks for the Pics. It pretty much confirm thats your problem. Those little breakouts cannot adequately heatsink the chips. The Aluminum heatsinks they have you stick on there, is utterly pointless by the way (; The DRV8825's chip die is heatsinked through the Bottom. A heatsink on the top looks pretty but does nothing to dissipate any heat away from the chip

    Read http://www.ti.com/lit/an/slma004b/slma004b.pdf for a better understading of why the "polulu footprint" style stepper drive for the DRV8825 is a bad idea. The document goes into detail of how these chips are actually heatsinked. It was born from the popularity of using the A4988 drivers on 3D printers, so Pololu went against what TI advises in the datasheet and tried to cash in on a 'footprint compatible' driver, that doesnt allow it to work at its peak (and even then its peak is way below your requirement)
     
    Rick 2.0 likes this.
  11. Travis Hamilton

    Travis Hamilton Well-Known
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    Thanks for all the input guys once again my *** has been saved i will get some better drivers. Should i still use the shield or just the arduino to hook the drivers to? Also i want to use the spindle on command in grbl to fire the torch but i think i need to change something in the settings anyone know what it is?
     
  12. Travis Hamilton

    Travis Hamilton Well-Known
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    Anyone use arduino for plasma? Any tips on setting grbl up for torch control etc?
     
  13. Travis Hamilton

    Travis Hamilton Well-Known
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    So i got my new drivers and i hooked up the y axis it still moves the right distance but it is really slow i have tryed to change the feed rates but it just seems to go the same speed no matter what. Anything i need to change?
     
  14. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Post the output of your Grbl settings? (Run "$$" to dump the settings)

    Likely max feedrate is too low still
     
  15. Travis Hamilton

    Travis Hamilton Well-Known
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    Thanks for responding i figured it out i was using imperial feed rates in my cut file and when i input commands but grbl is reading it as metric so if my feed rate is f500 i thought this would be 500 inchs per min but it is mm per min so the feed rate needs to be like 12700 mm per min lol and ya i had to increase my max feed rate also
     
    GrayUK likes this.

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