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  1. #1
    Engineer-in-Training
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    Auto Bed Levelling Glitches

    I apologize for creating a new thread about auto levelling...I hesitated in posting several different threads about my quarrels, so I thought it would be best if I started a new thread.

    I've just finished installing and updating my printer with the auto bed levelling set up, and was wondering if this is normal

    On a cold startup, entering G28 homes all my axis's like it normally does (goes to 0,0,0 and then the arm comes down on the servo and gets the z-end-stop)
    I then run a G29, which then starts it's first probe at 0,0 like G28 and continues in its grid probe from the 0,0 origin.

    However, if I run G28, and then a second G28, once it homes the X,Y it goes to the middle of the bed. Running a G29 after this from the middle of the bed, the gird is much more centred on the bed vs only running g28 once.

    My question is, is this to be expected, and obviously, it's wise to run the G28 command twice before G29 so that it begins its probe from the centre of the bed?

    Secondly, I'm noticing a weird glitch in my servo itself. It seems that whenever the printer is powered, no matter which position the servo is in, it will twitch ever so slightly every few seconds. This becomes even more so when one of the axis' moves (for instance, during the levelling procedure( the servo twitches back and forth about 2 degrees. I thought maybe it was interference or maybe my wires were crossed, but everything appears to be working fine. Any ideas on the cause of that one?


    Cheers

    Ryan

  2. #2
    Super Moderator Roxy's Avatar
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    Quote Originally Posted by MiniMadRyan View Post
    I apologize for creating a new thread about auto levelling...I hesitated in posting several different threads about my quarrels, so I thought it would be best if I started a new thread.
    Given how long and how chaotic most of the Auto Bed Leveling threads have become... I suspect everybody is on-board for creating new threads for individual support issues.

    Quote Originally Posted by MiniMadRyan View Post
    I've just finished installing and updating my printer with the auto bed leveling set up, and was wondering if this is normal

    On a cold startup, entering G28 homes all my axis's like it normally does (goes to 0,0,0 and then the arm comes down on the servo and gets the z-end-stop)
    I then run a G29, which then starts it's first probe at 0,0 like G28 and continues in its grid probe from the 0,0 origin.

    However, if I run G28, and then a second G28, once it homes the X,Y it goes to the middle of the bed. Running a G29 after this from the middle of the bed, the gird is much more centred on the bed vs only running g28 once.

    My question is, is this to be expected, and obviously, it's wise to run the G28 command twice before G29 so that it begins its probe from the center of the bed?
    From what you are saying, my guess is you have safe homing turned on. Can you upload you Configuration.h file? And it would be really helpful to upload a short video of it doing what you asking about.

    Quote Originally Posted by MiniMadRyan View Post
    Secondly, I'm noticing a weird glitch in my servo itself. It seems that whenever the printer is powered, no matter which position the servo is in, it will twitch ever so slightly every few seconds. This becomes even more so when one of the axis' moves (for instance, during the leveling procedure( the servo twitches back and forth about 2 degrees. I thought maybe it was interference or maybe my wires were crossed, but everything appears to be working fine. Any ideas on the cause of that one?
    Most likely you can stop this by defining:

    #define PROBE_SERVO_DEACTIVATION_DELAY 500

  3. #3
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    Thanks Roxy, I appreciate the help! I've included my config.h and I will see if I can get a video tonight of the jerk. Looking at the comments though in config.h I think you're right about the deactivation delay....whoops, I should have looked more closely at the code!

    Edit, I threw together a quick animation to illustrate what I mean since I'm away from my printer, check it out here! http://minimadryan.com/i3v_example.swf

    Ryan

    Configuration.h

  4. #4
    Super Moderator Roxy's Avatar
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    I would like to see an actual video... But with that said, EXACTLY which version of Auto Bed Leveling are you running? Are you running the Dacb fork of the Marlin firmware? Or maybe the enhanced version at this thread: http://3dprintboard.com/showthread.p...ed-G29-command

    Because, that is not normal. I could believe something like this is happening if you are running the Dacb Marlin Fork because there is code in there to limit the probing to the size of the object that is going to be printed. If that is the case, we need to do some more work to make sure the coordinates between the GCode post-processing match the printers probe locations.

    Tell you what.... Can you also post your Marlin_main.cpp ? Between the Configuration.h and the Marlin_main.cpp it should not be too hard to figure out why bad things are happening.

  5. #5
    Technologist jtice's Avatar
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    I have noticed something sorta like this with mine.
    I have safe homing turned on, and most the time, it all works just as it should.
    But, there are random times when it goes to home with the 28 command, that it will not goto the center of the bed, it will home the Z axis at the X-Y home.
    When it does this, it effects the locations where it does its 9 auto leveling readings. The first row of readings will be in the far back, where it homed Y.
    It still works, but once it starts the print, it will also be effected, and prints it off center, toward the X-Y home corner.

  6. #6
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    Thanks guys, sorry for not uploading the video's earlier, I was at work, and all I really had access to was creating that animation.

    Anyways, here's the videos. The first link here is powering the printer, and then a single G28 followed by a G29. The second video is the same cold start with G28 then a secondary G28 followed by a G29.

    Video 1: https://www.youtube.com/watch?v=HPX7U34GF2I
    Video 2: https://www.youtube.com/watch?v=D3AJEj16r1U

    Interestingly, as long as Repeater Host is kept running through out, any secondary G28 command will behave like it does in the second video. That is to say that I can disconnect, power cycle and reconnect the printer, and as long as I've kept RH open, the second or any subsequent G28 commands will zero the axis and then return to centre.

    I'm running Dacb's firmware mod as at the time it had everything I needed in there, and pretty much configured already for me. I've included my Marlin_main.cpp as well

    Marlin_main.cpp

  7. #7
    Technologist jtice's Avatar
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    Hmm mine acts a bit differently than that.
    Like I said, sometimes it safe homes, other times it just homes in the corner.
    If it homes just in the corner, the 9 location grip that it tests for leveling will start more toward that back corner.
    If it safe homes in the middle of the bed as it should, then the 9 location pattern is centered along the bed.
    I have never tried running 2 G28 commands before the G29 command though.

  8. #8
    Super Moderator Roxy's Avatar
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    Quote Originally Posted by MiniMadRyan View Post
    I'm running Dacb's firmware mod as at the time it had everything I needed in there, and pretty much configured already for me. I've included my Marlin_main.cpp as well
    I looked at the Marlin_main.cpp vs. my Marlin_main.cpp. I have some questions about the sled docking but I think that is OK. I'll know more in a bit.
    Did you run the Post Processing GCode script to limit the size of the probed area?

    Are you giving it the G28 and G29 commands via the keyboard? Or are they coming from a GCode file? It would be helpful to see the GCode file you are trying to print also.
    Last edited by Roxy; 11-04-2014 at 10:00 AM.

  9. #9
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    No, can't say I have. Just followed along with the notes on Github and ZennMaster's notes for it on his blog too. I haven't run a print with it yet, or processed any gcode, just what you've seen in the video

  10. #10
    Super Moderator Roxy's Avatar
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    Isn't your origin in the back right of the printer? If so, you have it specified wrong in the Configuration.h file.

    Do you have a reason to have your Z axis movement so slow? It is at 2 right now. I'm thinking you can bump that

    #define DEFAULT_MAX_FEEDRATE {250, 250, 2, 22} // (mm/sec)

    up to 5 or 6 very safely. And you have the Z acceleration very low also.

    #define DEFAULT_MAX_ACCELERATION {1000,1000,5,1000}

    and similarly, on the

    #define HOMING_FEEDRATE {50*60, 50*60, 50, 0} // set the homing speeds (mm/min)

    That Z being at 50 can be bumped up to maybe 250. That will make the video's much less painful to watch!!!

    But here is the first stuff I question. You have:

    #define LEFT_PROBE_BED_POSITION 50
    #define RIGHT_PROBE_BED_POSITION 150
    #define BACK_PROBE_BED_POSITION 150
    #define FRONT_PROBE_BED_POSITION 50

    But you have your bed size set at:

    #define X_MAX_POS 250
    #define X_MIN_POS 0
    #define Y_MAX_POS 250
    #define Y_MIN_POS 0
    #define Z_MAX_POS 235
    #define Z_MIN_POS 0

    I think you should spread out your xxx_PROBE_BED POSITION's to use nearly the full range of the bed. I have mine defined as:

    #define LEFT_PROBE_BED_POSITION (X_PROBE_OFFSET_FROM_EXTRUDER+2)
    #define RIGHT_PROBE_BED_POSITION X_MAX_POS
    #define BACK_PROBE_BED_POSITION Y_MAX_POS
    #define FRONT_PROBE_BED_POSITION (Y_PROBE_OFFSET_FROM_EXTRUDER+2)
    Last edited by Roxy; 11-04-2014 at 12:55 PM.

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