Auto Bed Levelling servo lowering on start of print

Hi All!

I'm using marlin with a servo with a microswitch to do the auto bed levelling in nine points.

Since setting it up intermittently I have had the servo going down to the probe position right as the it begins a print.

So it goes something like this
- get the bed and nozzle to temp,
- home x/y and z axis,
- run G29... the nine points are probed...
- print begins, counts down to print while waiting at the 9th point..
- countdown complete; starts to go to the starting point of the print and simultaneously drops the servo to the probe position bending its mount and generally stuffing everything..

I just put tonights version of marlin up from the GitHub and now it seems even more consistent; it drops the probe when the print starts...

Please Please Please give me some ideas.. I have tried to change everything remounted servos and endstops in an attempt to change default positions but it always does the same thing!

Surely someone else has some idea why?

P.S. I use slic3r, but it doesn't seem to send anything like an M401 so I don't think its relevant..

Edited 1 time(s). Last edit at 01/29/2015 07:27AM by daggywood.

Your configuration.h file looks fine. Please post the beginning G-code of one of your problem prints...

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-David

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Hi David,

Thanks for having a look at my configuration file..

I have included the Gcode I was using last night during consistent issues..

I tried running G29 Manually before running the print on printerface, and also i earlier I tried including the G29 in the code from slicer... both gave the same result.

perhaps I should add a M401 or home all axis after the bed probing??

I usually end up turning off the printer, restarting pronterface, pressing reset, turn it all on and set temps, then once temp is reached, i run the homing for all axis, then G29... sometimes it works authorities it will lower the probe and .... destroy stuff.

Hmmm... Not much there (a few odd commands, but nothing that would lower the servo)

Please copy/paste the Custom G-Code you have in Pronterface's start/end boxes.

Also, please let me know how the servo is connected to the RAMPS1.4 board.

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-David

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Wait... Try this first:

In your Configuration.h file, comment out the following line:

#define Z_PROBE_REPEATABILITY_TEST  // If not commented out, Z-Probe Repeatability test will be included if Auto Bed Leveling is Enabled.

Now try a print...

---

-David

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Okay - I must be looking at this with a new set of eyes this morning...

I also noticed in your Configuration.h that the probe offsets look a little wonky.

  #define X_PROBE_OFFSET_FROM_EXTRUDER -7
  #define Y_PROBE_OFFSET_FROM_EXTRUDER -39
  #define Z_PROBE_OFFSET_FROM_EXTRUDER -4.5

This places the probe only 4.5mm below the extruder... I suspect that you have the offsets for Y and Z swapped.

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-David

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Hi David, thanks very much again for you help..

As you suggested i tried the commenting out the Z_PROBE REPEATABILITY TEST... Made no difference..

I also tried including the G28 and G29 commands in the slicer add to start end.. didn't make any difference.. still lowered the probe when the print started..

By the way I am absolutely sure that those X Y Z dimensions are correct, my probe when lowered is only just below the extruder, this was because I mount the servo on the top of the x-carriage so it doesn't get too hot (as previous attempts resulted in dead servo's that lowered during long prints... I thought due to overheating)?

Anyway I went through each G code line one by one to find the offending line, I found that it was

G1 E-2.00 F2400.000

So it appears to be linked to the extruder..

Another interesting thing is that it happens every single time now.. not just intermittently....

I have a ramps 1.4 and its wired up to the 'servo' as shown..

update: just worked out it jitters in the down position after the extruder is used.. until the motors off is selected....

I think I have a short in my system between the extruder stepper and servo, gonna need to check that now I think..

Could you check another servo connector maybe? There's a few more connections for your servo, those could work.

Edited 1 time(s). Last edit at 02/02/2015 04:14AM by Ohmarinus.

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http://www.marinusdebeer.nl/

Hi Ohmarinus,

I'll give that a try.. Because I checked for short circuits and couldn't find any.. I'm also going to check my pins.h to see which ones are defined for the servo. and stepper.

changed it to the 3rd servo or Servo 2.. on pin 5 and the servo still moves and holds with the extruder..

not sure what i have isolated there. I'll have to think it through..

I tried plugging a new servo in, directly to the board and no issue during extrude, then i tried the new servo at the probe end of the loom and the issue reappeared.. I get the feeling my wiring might not have a direct short but has serious interference.

I'm using computer ribbon cable, which is neat and supports my 500mm Z height but might not be up to protecting the servo from steppers! I'll patch another loom around and see if it fixes it.