Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: SScnc on August 01, 2012, 05:42:47 PM
-
I have my spindle setup with PWM output to a Digispeed XL and finally to a GS3 VFD. The problem is the spindle fluctuates only when an axis is moving. If the machine is still the spindle is stable. As soon as it makes a move on any axis, the speed drops. Any ideas?
Thanks
-
I have never used PWM or indeed any VFD spindle control from Mach but I have something in the back of my mind about pulse width, try setting 5 in motor tuning and see if that makes a difference.
Hood
-
Just tried it. No change.
It's worse the higher up in RPM. Very strange. It only does it when I move an axis.
-
Hi,
Step pulse width has nothing to do with the PWM output.
On the surface it sounds like EMI is getting into the PWM signal. What PWM base frequency are you using? It should be set to 50Hz.
Cheers,
Peter.
-
That was my next assumption. I have the frequency set at 50hz.
-
Well I don't think noise is the issue. I put a 1uF cap on the output and I have the same result. Any other ideas? Any settings on the Digispeed I'm possibly missing?
-
If I were to use the Digispeed XL as STEP/DIR instead of PWM, what motor tuning values should I use?
-
Hi,
The DigiSpeed Step/Dir is not compatible with Mach3. It is for TurboCNC
The inputs to the DigiSpeed are filtered on board. The are no settings on the DigiSpeed that could be causing a fluctuation
I'm wondering if there is something with Mach3 that is causing it?
Have you done a Mach3 driver test to see if it is fluctuating?
Also do you have an oscilloscope to look at the PWM signal?
Cheers,
Peter
-
Hi,
The DigiSpeed Step/Dir is not compatible with Mach3. It is for TurboCNC
The inputs to the DigiSpeed are filtered on board. The are no settings on the DigiSpeed that could be causing a fluctuation
I'm wondering if there is something with Mach3 that is causing it?
Have you done a Mach3 driver test to see if it is fluctuating?
Also do you have an oscilloscope to look at the PWM signal?
Cheers,
Peter
That would explain why I couldn't get the step/dir to work. I'll have to run the driver test. I've done it in the past and everything looked okay IIRC. I don't have an o-scope unfortunately.
I emailed you a few weeks ago about the Digispeed and how I can't get more then 7V back to my VFD. I still have that same issue and I wonder if it is somehow related to this issue. Maybe my Digispeed board is faulty?
I compensated for the lower voltage by programming the VFD Analog Input Gain. Which works but I'd really like to know why I can't get 10V out.
-
Hi,
It is unlikely that the DigiSpeed is faulty as I test them all myself. That said it is possible.
Can you take an image of the DigiSpeed so I can see if I can pick anything with the board and check the up the jumper settings.
If the VFD is providing 10V to the Digispeed, you should be seeing a max of at least 9.4V
Cheers,
Peter.
-
I'm getting 10V from the VFD. But like I said only around 7V out. Picture attached.
-
I have a hunch the Digispeed is the problem. I uninstalled Mach and reverted back to two previous versions. And both versions acted exactly the same. I really need this fixed.
-
Hi there,
just a thought.Can it be possible that the power source voltage drops when the axes moves?
I found something similar when I tested something. This caused that the voltage dropped.
In other words, the votage drops below 13 V ( in my case ) and than the PWM output voltage
drops also below 10 V
Alex
-
My VFD supplies the 10VDC and it's constant, no variance. I'm almost sure its the Digispeed. If I don't figure it out soon, it's getting pulled out and I will go to CNC4PC.
-
Hi,
I couldn't see anything wrong with the jumper settings. The fact it works when the axes are not moving indicates that it is unlikely to be the DigiSpeed. If the system is generating sufficient noise to interfere with the PWM signal to the DigiSpeed, then that is an issue that should be addressed. Without an oscilloscope to see what is going on with the PWM signal from Mach3, it is very difficult to determine the cause of the problem.
Do you have an index sensor connected? And do you have spindle closed loop control selected. If so this be causing a problem.
In the end, if you can't get it to work, or are not happy with it, return it and I will refund the cost of the DigiSpeed.
Cheers,
Peter
-
Peter, unfortunately I was forced to replace the DigiSpeed with a C41 from CNC4PC because I just couldn't get it to work properly. After swapping the two boards, my spindle fluctuation is gone. It's a shame too because what drew me into the Digispeed was the built in circuitry to hook up an index sensor.
I will be sending you an email shortly about returning the DigiSpeed.