Z-Axis Headaches!

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  • #3650
    SystemsGuy
    Member

    Hey guys, ordered a TinyG a week or so ago, and finally had time to play.  I’m using it to control a Shapeoko, and have the X & Y axis working a treat.  I converted Alan’s config, and am using that.

    When I try and tune the Z-Axis, I get very inconsistent results with the below settings.  The motor vibrates, sorta like it’s over-driven, and drops steps if it turns at all,  but not quite the same – hard to describe.  The Z-Axis mechanics are fine, and I can drive the same motor / axis with a Pololu board without a problem.  I can swap X/Y with Z and the problem follows the Z axis.

    In a fit of troubleshooting, I tried changing the steps per mm for Z from 1.25 to 10.  If I do this, my stepper starts acting normally!?  I also tried varying the feedrate, but was really not able to produce consistent results with $3tr set to 1.25 at all.  Same results varying the microstepping – seems like the only thing that made a consistent difference was the steps/mm.

    I’m using Kysan 1124090 steppers on all the axis, a 32amp 12vdc power supply.  Swapping back to a RAMPS board with the same motors and power supply works fine as well.

    I’m sure there’s something fundamental I’m overlooking – just can’t figure it out!  Here’s the setup I converted from the .h file on the shapeoko wiki.

    G21
    $1ma=x
    $1sa=1.8
    $1tr=34.5
    $1mi=8
    $1po=0
    $1pm=1

    $2ma=y
    $2sa=1.8
    $2tr=34.5
    $2mi=8
    $2po=0
    $2pm=1

    $3ma=z
    $3sa=1.8
    $3tr=1.25
    $2mi=8
    $2po=1
    $2pm=1

    $xvm=16000
    $xfr=16000
    $xtm=170
    $xjm=5000000000
    $xjd=0.05
    $xsm=1
    $xsv=-1000
    $xlv=100
    xlb=2
    $xzb=1

    $yvm=16000
    $yfr=16000
    $ytm=170
    $yjm=5000000000
    $yjd=0.05
    $ysm=1
    $ysv=-1000
    $ylv=100
    $ylb=2
    $yzb=1

    $zvm=1200
    $zfr=1200
    $ztm=50
    $zjm=5000000000
    $zjd=0.05
    $zsm=1
    $zsv=-400
    $zlv=100
    $zlb=2
    $zzb=1

     

    • This topic was modified 11 years, 11 months ago by SystemsGuy.
    #3652
    SystemsGuy
    Member

    So after a bit of a rest, and coffee, I’ve solved my problem, but I’m not 100% sure I understand why.  Setting the max_travel_velocity t0 < 1000 seems to work – which I assume is dropping the step rate the board is try to push out to the motor, and making things happy.

    Is this a function of my motor choice or simply the max the board can support – or both?!

    #3653
    alden
    Member

    Mr SystemsGuy,

    Thanks for sticking with it. I actually drafted a response earlier but didn’t post because I wanted to fry a few things out first. But you beat me to it.

    The Z axis on the Shapeoko (or ANY machine) can be tricky if it’s not perfectly aligned.

    -I’d start with the machine and see how free you can make the Z axis spin – mechanically. You might try some light oil in the delrin nut as well.

    -The next place to look is the current setting on the Z axis. It might be able to go up a bit. If it starts cutting out due to thermal overload you have gone too far.

    -You might also drop Z down to 4x or 2x microsteps. You will get more torque at higher speeds this way. Balance torque with smooth operation

    Thanks for checking back in. I’ll probably change the default Z setting in the profile to 1000 so people can tweak up from there instead of hitting a problem. How about those 16,000 mm/min X/Y rapids!

    Alden

     

     

    #3743
    althiels
    Member

    I am pretty sure I was running into the same problem, thanks for working through it! Changing zvm from 1200 to 900 definitely helped and allowed my motor to operate without freaking out.  I am going to work on shimming it to eliminate the wobble (the shaft diameter is slightly smaller then the coupling ID, causing me to have to crank down on the set screw to get it tight enough and probably resulting in misalignment).  At least I know now that I don’t have a bad motor.  -Thanks!

    #3746
    alden
    Member

    You may also try dropping Microsteps to 4x or 2x, or try lowering the max jerk ($jm)

    #3765
    althiels
    Member

    I dropped the microsteps to 4x which helped a little, but I still had a good amount of noise/vibration coming from the z axis.  I did end up resolving it by adding a little light oil to the threads of the screw above and below the delrin nut which seems to have smoothed things out.  Probably should have done that in the first place but I thought I would mention it here in case others run into the same problem.  I ended up also ordering the acme screw upgrade so we will see how that goes.

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