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Offline CX15

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GoTo Zero not working
« on: April 14, 2018, 05:35:03 AM »
Hi All.

My new machine is up and running, but there's a few niggles :-(

When I hit GOTO ZERO in Mach3 the steppers on X and Y scream and although there's some movement, the spindle does not move to the correct position.
Z-axis behaves correctly.

Motor tuning (as per manufacturer) as follows:

Steps per: 320
Velocity: 4000
Accel: 300
Step Pulse: 0
Dir Pulse: 0

If I jog the X/Y axis using computer arrow keys, the unit moves smoothly and without problems at 4000mm per minute.
When I use "Ref All Home" function, it also moves smoothly and without problems.

When I change the Velocity down to 1000 things get "slightly" better.
The unit does move back to zero position, but it does it in a pulsing movement in stead of a smooth movement.
But this does not really solve the problem, as everything is very slow like this.

With some experimenting I found some other interesting behaviour as well:

When I execute this command
 
Code: [Select]
G0 X0 Y0
Same problem: screaming steppers, pulsing movement.

But if I execute this:
Code: [Select]
M03 S15000
G0 X0 Y0

the machine works perfectly fine (smooth movement). I dont understand why turning the spindle on makes the G0 command work differently.


I'm new to Mach3 and GCode, so I have no idea if this is normal behaviour, the CNC machine or Mach3 being the problem.

Any insights will be greatly appreciated.
Re: GoTo Zero not working
« Reply #1 on: April 14, 2018, 03:15:02 PM »
Hi,

Quote
the steppers on X and Y scream and although there's some movement

That's the steppers having stalled. You need to reduce the speed/acceleration until they are reliable OR increase the voltage of the power supply and drivers so they can go faster OR
replace the steppers and/or drivers with more capable units.

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

Offline CX15

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Re: GoTo Zero not working
« Reply #2 on: April 15, 2018, 04:32:31 AM »
Hi Craig

I dont think the speed is set too high.

As I explained above: Jogging works perfect. Ref All Home works perfect and a G0 (after a M3) also works perfect.
No stalling, no screamingm just smooth movement at the defined max speed.

It's only the Go To Zero function that creates the problem
Re: GoTo Zero not working
« Reply #3 on: April 15, 2018, 04:44:17 AM »
Hi,
jogging is seldom at the fastest possible rate. It may be that your motors can jog at 50% of max but fail at 100%.

Screaming steppers have stalled. It is indicative that you have the speed too high for the steppers/drives/power supply, it is not a normal condition for Mach3.

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

Offline Tweakie.CNC

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Re: GoTo Zero not working
« Reply #4 on: April 15, 2018, 04:57:26 AM »
Quote
I dont think the speed is set too high.

As Craig has said your Velocity / Acceleration settings are set too high for your machine as it stands.

Quote
As I explained above: Jogging works perfect. Ref All Home works perfect and a G0 (after a M3) also works perfect.

Just a guess but what I think you are finding here is a Mach3 peculiarity or limitation relating to the blended axis velocity of the Go To Zero function.

Tweakie.


Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: GoTo Zero not working
« Reply #5 on: April 15, 2018, 05:07:28 AM »
Hi,
may I suggest slowing it way way WAY down until it works properly and THEN start to speed it up until you find the limits.

All we know for sure at the moment is that you are trying to go too fast....by how much we don't know yet and wont until you slow it down enough to find the limits
of performance. Then it appropriate to ask 'is this right...or is there some fault?'

Try speed of 500 and an accel of 100.

Keep upping the accel until it starts missing steps or stalling, then back it off 25% Then work on increasing speed until a fault occurs.

Note you need to use G0 MDI commands so that you are testing the same thing...jogging is not scientific enough to give you useful comparisons.

Craig
My wife left with my best friend...
     and I miss him!
Re: GoTo Zero not working
« Reply #6 on: April 15, 2018, 05:38:21 AM »
Hi,
thinking also about the situation you describe where it seems to work if the spindle is running but plays up when the spindle isn't running.
You're right it shouldn't make any difference.

Does the power supply run both the spindle and the stepper drivers? I suspect it does.
Is the power supply a switching supply or analogue, I'm guessing a switching supply?

My guess is that the load on the power supply with the spindle running is sufficient to somewhat 'quiet' the switching supply such that the stepper drivers work better.
If that's the case you have a crap power supply, do yourself a favour and get a kick-arse analogue supply, they work so much better and so much more forgiving.

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

Offline CX15

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Re: GoTo Zero not working
« Reply #7 on: April 15, 2018, 05:43:42 AM »
Thanks Craig

I will investigate your suggestion.

However, in my tests the spindle was actually NOT on (VFD is switched off).
But just the fact that there was a M3 command seemed to make the difference.

I also tested the speed and when I use jogging (keyboard arrows), the gantry moves at the dialled in max speed (4000mm per minute).

Re: GoTo Zero not working
« Reply #8 on: April 15, 2018, 05:50:01 AM »
Hi,
well can rule out some sort of power supply interference.

I cant think of any reason that an M3 command would make any difference to a subsequent G0 move.

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

Offline CX15

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Re: GoTo Zero not working
« Reply #9 on: April 15, 2018, 05:53:50 AM »
The M3 also makes a difference to a subsequent G1 command

This
Code: [Select]
M3
G1 X0 Y0 F1000
works as expected. Roughly 1/4 speed and smooth movement to 0,0.

But if I just run this alone:
Code: [Select]
G1 X0 Y0 F1000
The movement is pulsating.