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Author Topic: Very odd rapids stepper motor stalling problem  (Read 25944 times)

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Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #50 on: February 23, 2013, 08:42:41 PM »
Thanks, can you do the same program only the first move be in the same direction as it is going now but only by the amount you have BLC set up for each axis then feed to the original position in your test.  I want it to take 2 moves to get to the position.  First position will be equal to BLC, second will be remainder of the distance needed.

Brett
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Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #51 on: February 23, 2013, 08:44:49 PM »
Thanks!
yah I totally agree with the conservatism. My max is actually on the order of 130ipm. I have tried to alleviate this problem with 50 ipm, which would be ~38%, and I still have problems with this one particular oddball scenario.  In fact, if I turn OFF backlash comp I can run this section of code at 120 ipm no problem, did it earlier today just for demonstration sake.  

I have milled dozens of projects, with lots of rapid changing of mill direction and lots of rapids. This may be the first time I've ever encountered a rapid move that involved such a short move on one axis. I am really starting to wonder if this little phantom un-programmed lurch is happening, but when played out at my normal move speeds is forcing my motors into a frequency well above what they could reasonably step. Then, once they are out of phase as it were, its just a good old fashioned stall :\

For all I know, when I'm commanding a G0 move, the backlash comp might be signaling a lurch at 200 ipm... just not sure yet.  That woudl be incredibly odd, but I'm trying to find a scenario wherein this problem only creeps in under these very particular circumstances, and this is where that path has led so far.

Offline RICH

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Re: Very odd rapids stepper motor stalling problem
« Reply #52 on: February 23, 2013, 08:45:39 PM »
I used CV, exact stop, different look aheads with values from 20 to 100 and never had problems.
I will remark that that was some time ago, but, why in the world do you have you Backlash Speed set to .9%?

I suggest that you just play with the backlash setting, and watch carefully what happens to see how it is implemented.
Sorry, have not read this thread completely, so maybe I'm not getting the gest of it.

RICH

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #53 on: February 23, 2013, 08:48:26 PM »
@Rich  yes sir this thread has been a doozy hehe!  It was wisely suggested that i turn down my ramp rates and bc%speed settings to better see what was going on, thats the only reason I'm running so slow is for diagnostic purposes

@Chaoticone I'm not quite sure I follow this request.  Do you want me to move +x +y to the turnaround point, then program in a very small -x -y move equal to backlash dimensions, THEN go on with the rest of the rapid?

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #54 on: February 23, 2013, 08:56:39 PM »
OK, say you got from xo yo

G0 X0 Y0
G1 F30 X-2 Y-2
X-1.996 Y-1.996  *If backlash is set to .004
X0 Y0

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 RICH

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Re: Very odd rapids stepper motor stalling problem
« Reply #55 on: February 23, 2013, 09:01:03 PM »
Quick read of this thread.
What size steppers are you using ....in-oz?
RICH

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #56 on: February 23, 2013, 09:04:34 PM »
@Chaoticone
ok, thats what I assumed. I did that with the following code:

G1 X0.3382 Y1.8169 F20
G0 Z0.125
G1 X.3362 Y1.8129    <-- TAKE UP .002 AND .004 BACKLASH in the opposite direction ON X AND Y RESPECTIVELY
G0 X0.3359 Y0.522
repeat...

Running under the same snails pace settings this *seems* to alleviate the lurch condition in the Y axis. Tried under both ES and CV.

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #57 on: February 23, 2013, 09:06:59 PM »
@rich

282 oz-in iirc

geared down ~2:1 via toothed belt drive

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #58 on: February 23, 2013, 09:10:22 PM »
also @rich
its the same setup I've been using for years. only have any sort of problem with it with this very particular scenario

Offline RICH

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Re: Very odd rapids stepper motor stalling problem
« Reply #59 on: February 23, 2013, 09:27:02 PM »
I think your steppers may need to be increased, could be wrong.
I had a skipping problem that drove me goofy, and i tried all kinds of testing, until one day I really analyzed the mill and found that
when short moves were required ( like those that will be required for 3D machining ) you need motors that can provide for acceleration
and that means higher motor torque. I had 287's, worked with no problems for years, then when doing very small moves found that they became border
line depending on the code. Went to 500's and problems went away. Also did away with the backlash.

FWIW,
RICH