Messages

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 24, 2013, 09:19:10 PM »

they're rolled ball screws not ground, one ball nut per axis due to space limitations. Worse case is just under .004, which is a little above the .003 I see quoted most places that talk about ballscrews.  I could get sub .001 with a good ground screw, or I could upsize the balls in mine.

Or, a cheaper option, is to find a way to get mach3 to do what I expected it to do

Mind you even if mach3 does its compensation I wont be planning on doing any climb milling, but this little machine just doesn't warrant the expense of going to ground screws.

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 24, 2013, 07:34:30 PM »

http://www.machsupport.com/docs/Mach3_CVSettings_v2.pdf

interesting comment in there
quote:
Backlash Speed % of Max – This is needed because backlash compensation is not
constrained properly by the acceleration parameter. In a stepper system this will result in
lost steps if set to 100%, while in servo systems 100% is just fine

"not constrained properly by the acceleration parameter"??

yes, I will agree with that. 

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 24, 2013, 07:29:59 PM »

Agreed.  But having my circles circular to within .0005 instead of .002 is just so lovely   

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 24, 2013, 07:23:24 PM »

AHAHAHA touche, sir

As a matter of usability it seems very peculiar that there would be an obscurely named variable under general settings that had the capacity to override motor settings...
At least it seems like that shuttle wheel setting should be under the backlash compensation dialog box, right?  Right above the enable checkbox...

I would not have expected there to be another setting that affected BLC, and I would not have inherently known to look under general settings.

This still doesn't explain the odd lurching, but per the post above it may be an intended feature, but I dont see any way to control that feature. Some machines may run a screw preload that would preclude doing an incredibly rapid backlash jerk, so you'd think you'd want to allow some flexibility of control there.

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 24, 2013, 07:15:46 PM »

Sure will. I commented to someone earlier that it is like I have discovered a new virus, but unfortunately I am patient zero.

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 24, 2013, 07:13:41 PM »

That's very interesting Hood.  Yes, it certainly looks like there is a sudden move, but its AFTER the backlash comp move in my case (it registers on the mach3 screen DRO), so that may not be behaving as intended in this case.

It would be nice if there were a checkbox for this setting!  Maybe there is but its named something I am just too slow to pick up on...

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 24, 2013, 07:11:28 PM »

NO, I hadn't!  I remember adjusting that years ago, but in this recent episode I had not touched it. I just checked and it was set to 0.001!

I just googled it, as frankly I forgot what "Shuttle Wheel" settings do (yay for archaic names) and apparently that is tied directly to backlash acceleration rates... Boy am I glad you asked me this.  Apparently on servo systems they tend to run terrifically small numbers for this, but on stepper systems it should be quite a bit higher.

I just adjusted it to 0.050 and it does make a pronounced difference.  The odd lurching behavior is still there when I execute in slow-mo but seems somewhat dampened. 

This morning I changed my stepper settings to half step to just get some more torque until I figured out what was going on, so its not really an apples to apples comparison, but this is a promising lead.

Thanks for mentioning

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 24, 2013, 06:41:45 PM »

Ok, thanks for the heads up!  I'll have to give that thread a good read. 

Several years ago when I built this machine I worked out what my worst case torque requirements should be, and I had some margin iirc. I'm attempting to re-do those calculations now.  Bottom line is, I see a jog that mach3 is commanding when backlash compensation is enabled that I cant explain, and it is on the very axis that is inexplicably stalling for me.  Generically, the answer for a stalling motor is more torque.  If you have enough torque to extrude away the dovetails on your mill table, you will never have a motor stall So I expect that most people would just chalk it up to physics and walk away, either choosing to up motor torque or decrease their feed/acceleration rates.

I have enough torque that I dont necessarily have to have the endmill spinning to pull it through a peice of wood... - I have always been spindle limited on machining. I have done everything I can to generate the peak g-loads I could ever see on my table and I have always been unable to induce this oddball failure mode except for when I'm using backlash compensation and on very high aspect ratio moves. Throw in the odd lurch behavior and I become suspicious that either mach3 by default is doing something unexpected BY DESIGN, or one of my files has become corrupted, or there is some kind of either mechanical or electrical cross-talk between systems that is making this a nonlinear problem :\

I can upgrade motors and probably handle whatever accelerations mach3 feeds my gear, but it would be nice to understand if mach3 is systematically making people de-tune their machines to alleviate these little phantom failures that crop up that may or may not be associated with this peculiar jumping movement I've discovered.

I can work around this issue, I was just hoping someone reading the forum was so intimately familiar with the inner workings of mach3 that they would be able to give a little insight into how mach3 plans/executes moves like backlash compensation.  At any rate this has been a learning experience for me, and hopefully for others.

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 23, 2013, 10:12:37 PM »

All along its been a G0 move right there, and BLC has been having an affect. I dont know why it wouldn't, rapid moves need to be compensated too, right?

I can change the code and try again tomorrow afternoon when I'll have some time. I'm reaching the bad part of the time_of_day / IQ curve.

Thanks again for all the consideration

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General Mach Discussion / Re: Very odd rapids stepper motor stalling problem

« on: February 23, 2013, 09:48:44 PM »

Checked on my microstepping configuration btw: I am setup for 1/8 microstepping