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Dazed and confused (GRBL)

Discussion in 'CNC Mills/Routers' started by FatGut, Aug 28, 2017.

  1. FatGut

    FatGut Well-Known
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    Hello,
    I cant seem to figure the GRBL Settings out!

    My Set up is as follows,
    Open Builds C-machine with three Nema 23 stepper motors 1.8 deg. 2.8 amp.
    5volt 8amp switching power supply to Raspberry Pi with Protoneer CNC Hat, jumpers configured to 1/8 step with Genuine Polulu DRV8825 rated at 2.5amps max per coil and limited to 2.2amps per coil, drivers are set at VREF 1.0 for a 2 amp current flow. ( I know the specs are close to max but the machine is for hobby use) motors are supplied 12v 10amp from a switching power supply through the CNC Hat. BCNC Software
    GRBL Settings
    $0=10
    $1=25
    $2=0
    $3=0
    $4=0
    $5=0
    $6=0
    $10=1
    $11=0.010
    $12=0.002
    $13=0
    $20=0
    $21=0
    $22=1
    $23=0
    $24=25.000
    $25=500.000
    $26=250
    $27=1.000
    $30=1000.
    $31=0.
    $32=0
    $100=2560.
    $101=2560.
    $102=2560.
    $110=500.000
    $111=500.000
    $112=500.000
    $120=10.000
    $121=10.000
    $122=10.000
    $130=200.000
    $131=200.000
    $132=200.000
    With these settings i can get each motor to step in both directions but when I try continuous steps I get motor stall with a high pitched whine like the motor is at max rpm. struggled with this over the weekend and had to walk away and finally admit defeat and ask for help... Thanks in advance for any help!
     
    #1 FatGut, Aug 28, 2017
    Last edited: Aug 30, 2017
  2. Jonathon Duerig

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    Your steps/mm are extremely high ($100, $101, $102). And this means it is likely that your max mm/min settings ($110, $111, $112) are pegging your motors at their max rpm. You can jog a short distance, because your accelerations are low and so if you move only a bit, then it doesn't let your motors get to that max mm/min. But on longer distances, it will just keep increasing the speed until they stall.

    Try adjusting your steps/mm way down. Then you might be able to get to a point where you can move the steppers enough to actually measure and calibrate them so that they are accurate.
     
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  3. Gary Caruso

    Gary Caruso Veteran
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    I would start by turning your max speed (110-112) up to 1000 and the acceleration up to 500 (120-122)
    also at 1/16 you should be at 200*16 = 3200 / 8mm = 400 steps per mm.. if you are using TR8*8
    for screws you can use 1/4 or 1/8 step so 200*8 = 1600 / 8 = 200 steps per mm (for setting 100-102)
    What does it do for long jogs? like 100mm jogs are they smooth? what are your jog settings?
    I have no experience with that driver though might be something else.
    good luck
     
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  4. FatGut

    FatGut Well-Known
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    Jonathon,
    Thank you for the advice I will try your suggestions when I get home tonight and will update with results.
     
  5. FatGut

    FatGut Well-Known
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    Gary,
    I will try Jonathon's recommendations first and see what the results are then will try your suggestions and see what happens.
    Thanks for the help
     
  6. FatGut

    FatGut Well-Known
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    UPDATE

    Gary,
    Applied your suggestions and things got better still some stalling but not as bad as it was. I forgot to open my work shop up so when I got home last night it was 100 degrees inside so did not spend a lot of time but I appreciate the advice from both you and Jonathon, I believe I am on track now!
    Once everything is running correctly, I will post all settings I use and maybe it can help someone from having the frustrations I had.
    Thank you!
     
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  7. David the swarfer

    David the swarfer OpenBuilds Team
    Staff Member Moderator Builder

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    Hi @FatGut
    first you calculate the steps/mm for your system
    GRBL settings calculator

    Then you tune the max speed and acceleration: start low for both, increase max speed till it stall, back down 20%, then increase acceleration till it stall, back down 20%. This process has been detailed many times on this forum.

    Note that GRBL is limited to 30khz step rate so use the GRBLCALC above to check that your settings are not exceeding this. If they are, reduce the microsteps on your drivers and start over.

    Then you calibrate. HOWTO Calibrate your CNC Machine for MACH3 or GRBL

    PS: tuning is easier if you use relative motion mode. In your GUI find the manual command entry box and type
    G91
    and press enter. Now distances are relative instead of absolute.
    Now, assuming mm mode and that the head is on the left and front of the machine....
    G0 X200
    will move the head 200mm to the right
    G0 X-200
    will move it 200mm left

    similarly:
    G0 Y200 ; moves 20mm away from you
    G0 Y-200 ; moves 200mm back toward you.

    G0 Z100 ; moves 100mm UP
    G0 Z-100 moves 100mm down

    G90 goes back to absolute mode. Note that using Jog buttons in the GUI is not useful for tuning as jogging does not move at full speed.
     
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  8. FatGut

    FatGut Well-Known
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    David,

    Thank you for this information, I also noticed that my Anti - backlash nuts seam to be worn and cannot adjust them to work properly so I am currently ordering some from the open builds parts store and once received I will replace and start from scratch! I will research "Now distances are relative instead of absolute." to understand what that relates to in the CNC world!
    I truly appreciate all the help from everyone on the forum and will post results as soon as possible....
     
  9. David the swarfer

    David the swarfer OpenBuilds Team
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    Hiya

    Read all about it here G Codes

    Normally Gcode operates in absolute mode. You set XYZ to 0,0,0 for the part, then run the Gcode in G90 mode.
    This means that G00 X100 goes to coordinate 100 from wherever it is now. An absolute position.

    In G91 mode
    G00 X100
    will move 100 from where it is now in the positive X direction, ie relative to the current position
     
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  10. Jonathon Duerig

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    I would just note that while you should use a steps/mm calculator like David and Gary propose, this is the first step and not the last. Once you have things reasonably close to accurate, you will want to run some actual measurements. Tell your machine to move 150mm and then measure how far it actually moved. And then you may have to adjust the steps/mm by just a tad to make sure it actually matches the reality of your particular machine setup. And this has to be done independently for each axis. This matters more with some applications than others. Nobody would notice if a sign is 0.5% smaller when cut out. But if you are cutting out a panel which needs to be joined to other parts, it may mean that screw holes are systematically off or that two panels have a small gap or interference instead of meshing properly.

    -D
     
  11. David the swarfer

    David the swarfer OpenBuilds Team
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    \
    yeah, that is what I said, with a link to the resource with all the math you need to actually do it.

    "Then you calibrate. HOWTO Calibrate your CNC Machine for MACH3 or GRBL"
     
  12. FatGut

    FatGut Well-Known
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    David,

    Thanks for the explanation! I was researching it after I ordered my backlash nuts and ran across the same site you referenced.
    Thanks again for all the help!
     
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  13. FatGut

    FatGut Well-Known
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    *****UPDATE******

    I would like to thank everyone for there help and to the GREAT People at the Opebuilds store for there quick shipment of my parts order so I could work on this issue over the long weekend. I have got the machine moving and Calibrated pretty close to where it should be (I Know close is not good enough). I will get it where it needs to be soon.

    These are the steps I took to get it working:

    (1) replaced backlash nut on the "Y" axis (Might need to replace 8mm metric Lead Screw)

    (2) Set the protoneer boards jumpers to 1/8 step

    (3) Reset the VREF Voltage on the polulu DRV8825 drivers to 0.7 volts = about 1.2amps

    (4) used the GRBL settings calculator

    (5) Set the GRBL settings per calculator

    (6) jogged each axis

    (7) Calibrated all axis using HOWTO Calibrate your CNC Machine for MACH3 or GRBL"

    (8) Test ran some patterns through BCNC (No cuts just checking for proper movement)

    (9) Machine wiggled and and jiggled ( no motor stall or grinding noise)

    I will post all setting and parameters after I install all limit switches and E-stop and get all electronics in its case, and maybe post some pictures!

    Rick
     
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