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Author Topic: Very odd rapids stepper motor stalling problem  (Read 25940 times)

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Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #60 on: February 23, 2013, 09:31:45 PM »
I've looked at that as an option, I could drop the cash on that and give it  a whirl, but then when I see this peculiar jerking behavior generated by mach3 I'm not sure where the problem lies...
Its hard to put into words the various test programs I've run this setup through, and the only way I can generate this error is if I make a very small move on one axis while making a normal move on another.  So in terms of accelerations, I feel confident I've put the motors through much worse, completely without incident.

Also, dont know if you've ever seen the Hoss cnc conversion, but as it turns out he was running even smaller motors than I am, and his rapids are comparable to mine.  From what I gather I'm in good company on this size mill with these size motors, but I'll never turn down more power!! ARR ARR!

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #61 on: February 23, 2013, 09:48:44 PM »
Checked on my microstepping configuration btw: I am setup for 1/8 microstepping

Online RICH

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Re: Very odd rapids stepper motor stalling problem
« Reply #62 on: February 23, 2013, 09:53:25 PM »
Have some fun and apply your engineering talents to the problem.
Amount of torque required to just move an axis, axis torque profile over full travel, also on reversal,  torque required to accelerate for the smallest movement ratio in the time frame available from standstill and also when running at anticipated max feedrate, torque required for machining. Relate that to your motor torque curve for how it is wired. See what it tells you.

Nothing beats testing though........ and measuring some values. ;)
RICH

MODIFIED: never compare machines unless the systems are exactly the same, else , it's just somewhat relavent.
RICH

 
« Last Edit: February 23, 2013, 09:57:45 PM by RICH »

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #63 on: February 23, 2013, 10:02:12 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.

Even as it finished going to x0 y0 there were no lurches?

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 Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #64 on: February 23, 2013, 10:07:21 PM »
I'm sorry, in the code you posted, the last line is a G0, needs to be G1.  I dont think BLC has any bearing on G0s

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 #65 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

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #66 on: February 23, 2013, 10:16:14 PM »
I would say yes, rapid moves need to compensated I'm just not sure how or when they come into effect.

Thanks for testing.  It has been interesting to say the least.

Get some rest,
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 mc

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Re: Very odd rapids stepper motor stalling problem
« Reply #67 on: February 24, 2013, 06:04:05 PM »
odex, your problem sounds very familiar to a problem I have with my lathe (http://www.machsupport.com/forum/index.php/topic,23454.msg164689.html#msg164689 - read the bit below the quoted g-code).

I thought it was just an issue with the tool change and put it down to an issue between Mach and the SS, but as I can work around it, I've just been ignoring it. I've never actually tried a plain G0 move to see if the problem occurs without a tool change.

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #68 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.

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #69 on: February 24, 2013, 06:53:37 PM »
This has been for me as well odex.  Have you tried your test while adjusting the shuttle speed in general config?

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!