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Author Topic: Stepper motors stutter and stop when running g-code.  (Read 5911 times)

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Stepper motors stutter and stop when running g-code.
« on: June 25, 2008, 12:22:20 AM »
I have just finished my circuit and my stepper motors were working great.  Now when I run any g-code either either manual or a program the motors stop for a brief instance at the same time then start again.  They stop about every 1.5 rotations.  It does'nt matter if it is a rapid move or a slow feed move it always does it now.  What's weird is that I can jog it extremely fast and they never stutter at all.  The DRO on screen stops and everything.  I have messed with motor tuning settings with no luck.  Why is mach 3 doin this.  It just looks like the software is taking a break for a split second then it goes on. 

Any advice is helpful.
Re: Stepper motors stutter and stop when running g-code.
« Reply #1 on: June 25, 2008, 12:34:31 AM »
You might check to see that "Backlash Compensation" is not ON.
Does it do it during a straight move of one axis only ? Or only when interpolating ?

Offline jimpinder

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Re: Stepper motors stutter and stop when running g-code.
« Reply #2 on: June 25, 2008, 04:35:34 AM »
When you say 1.5 rotations - rotations of what? the motors themselves, your lead screw or what.

To get some idea of the frequency of this, what is your number of steps per  unit set at.

Does this occur on all axis simultaneously.

I have a similar little stutter in my system and little while ago - and I traced this to my 5 volt supply system - the voltage regulator was on the points of giving up - it did give up - so that was how I traced it.
Not me driving the engine - I'm better looking.
Re: Stepper motors stutter and stop when running g-code.
« Reply #3 on: June 25, 2008, 11:15:23 AM »
Its about 1.5 revs of the motor, 48 steps per unit.  And it really is not a stutter the motors actually stop completely then start again over and over.  I dont even have it hooked up to a machine yet I am just testing it first.  I just have my motors side by side on my bench.  If you tell it to rapid a few inches it will start to rotate then stop then start again, it looks like a certain increment before it stops, until it finally gets to where it is going.  And yes all axis stop and the same time when running both at the same time.  If a single axis move just that axis stops obviously.  What is weird is that it will jog just fine even multiple axis at the same time.  Its just when running code.  I had this problem the other day and I messed with the motor tuning settings and it quit.  At least thats what I thought helped it.

Thanks
« Last Edit: June 25, 2008, 11:20:35 AM by dwilley »

Offline jimpinder

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Re: Stepper motors stutter and stop when running g-code.
« Reply #4 on: June 25, 2008, 11:49:19 AM »
Your calculations for your motor steps per unit are way out.

Modern drives use microsteps (my Geckos have 10 - yours may be different - they may be switchable - if they are try 1/8th as a compromise). Modern motors are normally 1.8 degree motors so in themselves require 200 steps per rotation. So combined with the drivers they require 2000 steps per rotation - NOT 32.

If you then attach this motor to a leadscrew on a lathe or mill, the leadscrew will require a number of turns to move one inch - mine is ten, so I needs 20,000 steps. I also have a gear down system so my actual steps per unit is  60,000.

Set your steps per unit at what you calculate it will be on the mill you are building - or pretend - about 20,000 which isn't far off. The fill in your speed per axis at about 10 ins per minute, and set your acceleration at one.

See what the results are then.

Not me driving the engine - I'm better looking.
Re: Stepper motors stutter and stop when running g-code.
« Reply #5 on: June 25, 2008, 02:51:51 PM »
I have tried doing this but if you turn steps per unit up the motors cant respond fast enough and the just vibrate and dont even rotate.  I'm just testing with small motors so I dont damage my good motors.  The only thing this does is make the motors vibrate and if I run code they just stop vibrating for a second instead of stop rotating.

Offline Hood

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Re: Stepper motors stutter and stop when running g-code.
« Reply #6 on: June 25, 2008, 02:58:04 PM »
If you set the correct steps per unit and the motors just scream and vibrate that is because they are missing steps because your acelleration and Velocity are set to high. Set the Steps per unit correctly and turn the acell and Velocity way down then gradually increase the velocity testing the motors in between by pressing the up/down arrows. Once they start to miss turn it down a bit and then increase the acelleration in steps, you may have to mess around a bit to get the perfect settings for your individual  motors and drives.
Hood
Re: Stepper motors stutter and stop when running g-code.
« Reply #7 on: June 25, 2008, 04:05:51 PM »
All changing the settings seems to do is change the duration that it stays on before stopping.  It still jogs fine but stops and starts when running code.  I dont know what the problem is.  Sometimes it will do it and other times it doesnt.  It usaully does it only rarely when I try it will it run without stopping.

Offline Hood

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Re: Stepper motors stutter and stop when running g-code.
« Reply #8 on: June 25, 2008, 04:14:53 PM »
Press the Tab key and see what your slow jog is set to, might be that your slow jog is slower than your code movements and so goes over your motors limits.
Hood
Re: Stepper motors stutter and stop when running g-code.
« Reply #9 on: June 25, 2008, 08:39:53 PM »
I think I figured out what it is.  I uninstalled and reinstalled mach 3 and it is working better than ever the motors even move smoother now even in jog mode.  I think the driver was corrupt.  Thanks for the help.