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Offline Dax

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Stepper motors
« on: October 13, 2017, 07:59:47 PM »
Hi Guys
Having some trouble with random missing steps, my machine stops code continues to run in Mach 3 then machine goes again obviously in the wrong place due to the stop. Motors sometimes stall when I jog so I'm thinking it may be set wrong somewhere, I am hoping someone is able to tell me what my settings should be.
my machine info is
1600 steps
8 micro steps
15 motor teeth
leadscrew 30
leadscrew pitch 2mm
hope this makes sense to somebody. Its on a fully licensedmach 3 copy (to me). Thanks
Re: Stepper motors
« Reply #1 on: October 13, 2017, 08:03:35 PM »
Hi,
is this a new build machine? Or has this problem occurred in a machine that had otherwise bee working well?

Craig
My wife left with my best friend...
     and I miss him!
Re: Stepper motors
« Reply #2 on: October 13, 2017, 08:19:36 PM »
Hi,
you don't say what motion control you are using. If left to guess I would have to say parallel port with 25kHz kernel speed right?

A few calculations may be in order.

1600 micro steps per revolution with a belt reduction of 2:1 to the leadscrew= 3200 pulses per revolution of the leadscrew.
Therefore given the 2mm pitch of the screw 2 mm/3200 ppr= 0.625um per pulse.

If you are using Machs parallel port at 25kHz then the maximum speed of your motor is 25000 X0.625 um=15.625 mm/sec or 937.5 mm/min.
Do you have the velocity set higher than 937.5 mm/min, if you do Mach cannot issue pulses fast enuf to do that. You could improve this the maximum
speed but would need to make some more fundamental changes.

Craig
My wife left with my best friend...
     and I miss him!

Offline Dax

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Re: Stepper motors
« Reply #3 on: October 13, 2017, 08:30:14 PM »
I bought it second hand guy said he never had any issues (i'm inclined to believe him) literally had 10 hours use he didnt let me have the computer but it was on Linux anyway and I'm not a fan, its a Rhonmac as far as I know its stock and thats why I believe its a setting issue. Its on a parallel port how do I check the 25hz I'm a complete noob  

Offline Dax

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Re: Stepper motors
« Reply #4 on: October 13, 2017, 08:33:14 PM »
Mach 3 is set to steps per 2000 velocity 438 acceleration 187.5 I take it this is not right.
Re: Stepper motors
« Reply #5 on: October 13, 2017, 09:14:13 PM »
Hi,
no not quite.

First just to make sure go to Config/Select Native Units and make sure that mm is selected. You should not thereafter have to touch this setting.

Your 'steps per unit' should be easy enuf to calculate. The question is how many pulses does Mach have to issue in order for the axis to shift 1mm?
The pitch of the lead screw is 2mm per revolution, so 1mm movement of the axis requires the lead screw turn 1/2 a revolution. With a 2:1 belt
reduction the motor must turn one revolution, ie 1600 microsteps. Enter 1600 in the 'steps per' box.

We have already done the calculation for maximum speed, set that at 900mm/min, and in no case more than 937.5 mm/min. Recommend the acceleration
be kept deliberately very low. Once you've got things sorted then you start increasing it until it faults and the back off a bit. Start with accel at 180mm/sec/sec.

When you exit motor tuning do so with <SAVE AXIS SETTINGS>. Probably need to restart Mach to have the new settings take effect.

Now you need to test that axis. Let us know how you get on.

Craig
My wife left with my best friend...
     and I miss him!

Offline Dax

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Re: Stepper motors
« Reply #6 on: October 13, 2017, 09:37:42 PM »
Thanks I will give it a go :)

Offline Dax

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Re: Stepper motors
« Reply #7 on: October 13, 2017, 09:41:40 PM »
900 mm min seems very fast?! twice what its currently set to
Re: Stepper motors
« Reply #8 on: October 13, 2017, 09:59:22 PM »
Hi,
900 mm/min works out to 450 rpm for the leadscrew and 900 rpm for the motor. Yes it might be a bit quick but still within bounds.

I use Vexta 5 phase steppers with 10:1 planetary gearboxes on 5mm pitch screws and get 1200mm/min. That means my steppers are doing
2400 rpm. The 5 phases and the very high voltage drivers mean its perfectly possible. Most CNCers would consider 1200mm/min slow, without
gear or belt reductions and with decent steppers and drives many expect and get 5000 mm/min.

A production CNC machine is commonly 30-40 m/min and was reading the specs of a double column machine the other day that does 96m/min and
accelerations of over 5g!

There is absolutely no harm in reducing the speed if you think it too high. Remember that what your setting here is the maximum speed your machine
can go, sometimes called rapids, or traverse speed or G0 speed. It is not generally expected that you'll cut at that speed, that's done with G1 codes
which are carried out at a fraction of the max or G0 speed.

Craig
My wife left with my best friend...
     and I miss him!

Offline Dax

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Re: Stepper motors
« Reply #9 on: October 13, 2017, 10:12:51 PM »
wow I know so little, just thought with it missing steps faster would be worse. I will set it and try. cheers for the info.