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GRBL acceleration question

Discussion in 'Control Software' started by surfdabbler, Sep 17, 2020.

  1. surfdabbler

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    When using the laser etching of an image, it doesn't always seem to respect the acceleration. I've tried LaserGrbl, and also Lightburn, and both have similar results. Instead of coming to a smooth stop at the end of each pass, there is a big clunk as the head stops to come back the other way.

    The jogging controls seem to work OK, where I can jog one way, press the button to jog back again while it's still moving in the first direction. The head will smoothly stop and come back the other direction. However, with Lightburn, every pass ends in a big clunk, and the Y-Axis is also a big clunk for every small step. LaserGrbl seems OK if it's a full image, but if there is white space around the edge, and the laser doesn't go all the way to the end of the pass, then it clunks.

    How can I resolve this? Is there a parameter to adjust, or a GRBL software update?
     
  2. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Paste your Grbl settings please, so we can see if any look off
     
  3. surfdabbler

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    My settings are below. Acceleration settings were at 20 when I got the machine. I had configured the acceleration values up to 200, and this runs really well for jogging, and in other software, but with the clunky laser etching passes, I've had to pull the acceleration back down to 50. It's still clunky though. I can try to make a video if that helps.

    $1=25
    $2=0
    $3=6
    $4=0
    $5=0
    $6=0
    $10=1
    $11=1.000
    $12=0.002
    $13=0
    $20=0
    $21=1
    $22=1
    $23=7
    $24=25.000
    $25=500.000
    $26=250
    $27=2.000
    $30=10000
    $31=0
    $32=1
    $100=800.000
    $101=800.000
    $102=800.000
    $110=2200.000
    $111=2200.000
    $112=500.000
    $120=50.000
    $121=50.000
    $122=50.000
    $130=500.000
    $131=500.000
    $132=200.000
     
  4. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Video and sample gcode file would help yes :)
     
  5. surfdabbler

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    OK, here's the video...

    https://youtu.be/_NaNHlFSTlI

    I've attached two gcode files. The rectangle file clunks on every turnaround. The oval.gcode file seems not bad at the start, but in the middle, where the scan lines start and end at the same X position, the problem is at it's worst, and as it goes to the end of the file, it improves again. It seems to be related to one line starting in the same X position as the previous line ended.

    Any clues?
     

    Attached Files:

  6. surfdabbler

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    I've investigated this further today. I've updated to 1.1h, and it still has the same issue.

    It seems that once a G1 tool path has accelerated, it will abruptly change direction for subsequent G1 instructions. Perhaps it needs a G0 to end the path before it will slow down? Just moving around a square, the tool will move to the start point, accelerate onto the first side, then abruptly change direction at the next three corners with no deceleration, and at the end of the fourth side, it will decelerate again.
     
  7. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Is far off from the default of 0.010 (for more see gnea/grbl

    IMG_20200919_102218.jpg

    Restore all settings to defaults, see gnea/grbl

    Then load our Acro profiles from CONTROL (as you mentioned laser I assume Acro? - if its not custom values then, but don't change advanced defaults Grbl is pretty spot on. Just change laser mode, steps per mm, acceleration etc. Leave the planner settings default
     
  8. surfdabbler

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    That was it!! You are a legend, thank you.

    I took a snapshot of all the settings before I made any acceleration changes, and it was set to 1.000 from the factory. Very strange. Anyway, it's working beautifully now. I'm able to set the acceleration back up to 200, no problems.

    Thanks so much!
     

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