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Author Topic: Very odd rapids stepper motor stalling problem  (Read 26057 times)

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Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #20 on: February 23, 2013, 01:13:06 PM »
@angeltech

yes sir, that is correct, there is a threshold below which this error happens and above which it does not, iirc it was on the order of .006

its something to do with the aspect ratio, either hardware or software side. I have done everything I can to rule out hardware (that I can think of)

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #21 on: February 23, 2013, 01:23:41 PM »
Are you running in exact stop mode or CV?  Does it chage the results if you change the mode?

Brett
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Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #22 on: February 23, 2013, 01:27:16 PM »
During normal operation I run constant, but I have tried it on exact stop as well and I get the same lockup.

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #23 on: February 23, 2013, 01:54:11 PM »
Try setting your backlash comp speed to 0.1 and let me know how it does.

Brett
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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 #24 on: February 23, 2013, 02:07:04 PM »
great idea, I didn't even realize it would accept fractional values in that block.

SO IT GETS WEIRD.

with backlash compensation %speed set to 0.1, it very slow initiates its BC compensation move, which at 0.1 is very slow, then as soon as it gets to its rapid it hangs.

I rewrote the program to remove the x move ENTIRELY, and it works fine.

HOWEVER, at 0.1%speed I did notice that as its doing its backlash comp move, it creeps very very slowly, then takes a sudden jerk right before it hangs the motor, I will study the motion a little better and report back. Very odd.

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #25 on: February 23, 2013, 02:22:36 PM »
OK, so get this

Per advice above I ran the program at 0.1% blc speed.  I filmed this with my phone because it still happens a bit to fast to be sure whats happening, here is what I observed:  The motor creeps very slowly through what I assume is its backlash distance, then, it suddenly LURCHES forward some MORE.  NO IDEA what that is or why id does that. it looks to be doing this little jerk at the rapid speed.

The weird part is, when I run the edited version of the program, WITH NO X MOVE, it does not do this jerking behavior, it only does the very slow backlash compensation then goes about its business.

Is there something peculiar to the way mach3 does BLC that is biting me here??  is it having to interpolate how much to move each axis for the backlash comp and on a very small move on one axis it spills over data to the other axis??

this is an interesting development, I appreciate you suggesting the 0.1% speed idea.

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #26 on: February 23, 2013, 02:26:47 PM »
NOTE: I repeated the above, but this time with a motor acceleration rate of 1 programed in.  It again does its very slow approach to taking up the backlash, then makes what IS a rapid move (you can hear it ramping at the ramp rate), THEN it starts its rapid in earnest.  Mach3 seems to be sneaking in a rapid move here for some reason, and it seems to have something to do with the x axis moving at the same time. 

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #27 on: February 23, 2013, 02:30:14 PM »
ALSO note that I'm able to observe at these low speed settings that mach3 is in fact doing the backlash compensation as two seperate moves, first the Y axis, then the x axis. It may be doing this as a result of the magntitude of the x move??  I will test with different magnitude x moves and see if it still separates out the two axes.

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #28 on: February 23, 2013, 02:39:02 PM »
OK, new data:

I adjusted the program to make the x move go to x0.3 instead of x0.3359 (to make the x traverse distance larger), so instead of this:
G1 X0.3382 Y1.8169 F20
G0 Z0.125
G0 X0.3359 Y0.522


I INSTEAD USED THIS
G1 X0.3382 Y1.8169 F20
G0 Z0.125
G0 X0.3 Y0.522


The y axis motor does the same little odd jerk, but to a much smaller degree!!

Now, when I re-write the code again to this:
G1 X0.3382 Y1.8169 F20
G0 Z0.125
G0 X0.2 Y0.522


The y axis motor does a nice smooth transition, so, somehow or another mach3 seems to be signaling a hidden little rapid move right after the backlash compensation, and it somehow is in proportion to the magnitude of the attached x move.

SO now I know:
1) its related to high aspect ratio moves
2) its related to use of backlash compensation
3) it involves a sudden rapid move right after the BLC move
4) the magnitude of the jerk is related to the magnitude of the other axis movement.

man am I glad I decided to post here today haha. At least I understand it a little better now.

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #29 on: February 23, 2013, 02:41:15 PM »
OK, can you try those same test in CV mode and exact stop?  This is interesting.

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!