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Author Topic: Very odd rapids stepper motor stalling problem  (Read 25934 times)

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Offline Hood

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Re: Very odd rapids stepper motor stalling problem
« Reply #70 on: February 24, 2013, 06:57:57 PM »
I am not sure if the way Backlash is done has been changed but I do know that at one point in time Brian was talking about sending a very fast rate to the axis to take up the lash, much faster than the accel/velocity in motor tuning. The theory was that as the motor had no load of the axis then it could do that without risk of stalling. I think that is the way it is done in the Smoothstepper but as said not sure if it was changed to do it that way if using  the parallel port.
Hood

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #71 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

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #72 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...

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #73 on: February 24, 2013, 07:14:44 PM »
 :)  Good, it will be interesting to see how and when it changes the moves BLC generates.  Please do keep us posted as this has been the most intensive testing posted so far that I'm aware of.  You have a great test bed.

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #74 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.

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #75 on: February 24, 2013, 07:16:13 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...

Thats the backlash Comp. enabled checkbox.   ;D

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #76 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.

Offline RICH

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Re: Very odd rapids stepper motor stalling problem
« Reply #77 on: February 24, 2013, 07:24:19 PM »
The only way to good flavor of how BC is implemented is to just be very attentive to what is happening.
What one sees becomes a little deceptive when starting at a crawl to implementing at a fast rate.

FROM OTHER REPLIES I have made on the subject:
The Shuttle Wheel Accel is in seconds. How exactly is the" time" applied to the backlash "cycle"? Well I don't really know.
 It's internal to Mach. By observing the difference in how the motor reacts to different settings you will see that it affects the overall time
 it takes for Mach to take up the backlash and at say a value of 5 you will find that over five seconds the handwheel / shaft will turn
 rather slowly. At 0.005 sec its almost instantaneous. In the real slow setting, and say you jog a distance of .1"  you will find there
seems to be almost 3 distinct motor responses in the cycle,....... a small rotation then deceleration...... then backlash taken up
over a time...and then  accel and move to finish the distance.

So to get of flavor of it you need to start slow, observe, listen to see what is happening over an operating range.
Work your way up in settings.

When implemented in rapid movement it can change some of the required torque values just because of the applied BC mechanical movements.
There may be some quirks in MACH on it's implemenation depending on the conditions.....I don't really know .......

I will repeat that if you get rid of the need for BC you'll be a much happy camper in the long run.

RICH
« Last Edit: February 24, 2013, 07:29:00 PM by RICH »

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #78 on: February 24, 2013, 07:29:59 PM »
Agreed.  But having my circles circular to within .0005 instead of .002 is just so lovely   :-\

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #79 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.  >:(