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Author Topic: Very odd rapids stepper motor stalling problem  (Read 25943 times)

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Re: Very odd rapids stepper motor stalling problem
« Reply #10 on: February 23, 2013, 12:23:36 PM »
are you using backlash comp.

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #11 on: February 23, 2013, 12:29:55 PM »
yes. its fairly small,I think .004" on my worst axis.

UPDATE:
I rewrote the test code to use G1 moves instead of G0, and I'm using a speed of 30 ipm (which the machine is grossly over-capable of executing).

With backlash compensation ON, it stalls.
With backlash compensation OFF, it works!!

interesting development...
Re: Very odd rapids stepper motor stalling problem
« Reply #12 on: February 23, 2013, 12:33:28 PM »
why are you using backlash comp?.

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #13 on: February 23, 2013, 12:34:32 PM »
Also, I tried playing around with the % of max setting in the backlash comp

dropping it all the way down to 1% I still get a problem, so long as blc is enabled.

Disable blc, and the world is right again.

This feels like progress... or maybe just a new hole to dig in... haha

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #14 on: February 23, 2013, 12:35:58 PM »
For overall positional accuracy. Accumulating a series of .004 move errors over the course of a program run can net a fairly sloppy result on the finish pass

Offline Chaoticone

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Re: Very odd rapids stepper motor stalling problem
« Reply #15 on: February 23, 2013, 12:47:48 PM »
I think your accel rates are too high.  Short snappy moves will show this.  Backlash comp. will as well.  There isn't enough time to change direction of the motor and all the mass hooked to it.  All of this has to be done in a fixed time window so your path will be accurate.  Naturally a huge Arc allows time for an axis to slow and change direction.  I know your machine can travel much faster than you typically run or even rapid at, but it doesn't have the guts to snatch the amount of mass around your trying to in such a short amount of time even though it is a short distance.

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 #16 on: February 23, 2013, 12:53:58 PM »
I thought that initially as well, but if I go and change that sample code to make a larger move in the x axis (go wild, make it move 9 inches instead of .00x), it will execute without flaw. I can do drills all day where I rapid back and forth on any axis or any combination of axes. 

If for instance I REMOVE the x move from that sample code, the y axis WILL NOT stall anymore. Conversely, doing the x axis move by itself will not cause a problem. The x axis move shouldn't really affect it (stepper should have peak torque at very very low speed), but it does.

You are right, there is certainly an inertial mass effect, but why wouldn't it show up when making rapids in any other way?  Its only the high aspect ratio (between move ordinates) that draws this problem out.
Re: Very odd rapids stepper motor stalling problem
« Reply #17 on: February 23, 2013, 01:09:43 PM »
try making the x move .015, as this is easily above the backlash value.
Re: Very odd rapids stepper motor stalling problem
« Reply #18 on: February 23, 2013, 01:10:53 PM »
if that works bring it down to .010 then .006. It should stall at .006

Offline odex

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Re: Very odd rapids stepper motor stalling problem
« Reply #19 on: February 23, 2013, 01:11:31 PM »
To address the inertial mass concern I just wrote and executed the following code several times:
G0 x0 y0
x.050
x0
x.050
x0
y.050
y0
y.050
y0
x.050 y.050
x0 y0
x.050 y.050
x0 y0

as you might imagine this produces very rapid, jerking motions of the table, its kind of violent even, but when its all said and done it returns exactly back to where it started without any motor stalls.
This is with backlash comp turned on.