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Author Topic: Help Please with PWM Spindle Motor Speed  (Read 13262 times)

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Re: Help Please with PWM Spindle Motor Speed
« Reply #20 on: November 13, 2014, 05:57:50 AM »
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Re: Help Please with PWM Spindle Motor Speed
« Reply #21 on: November 13, 2014, 07:47:58 AM »
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Help Please with PWM Spindle Motor Speed
« Reply #22 on: November 16, 2014, 07:23:09 AM »
I suspect you may have a couple of basic problems.  First it is likely that the PWM speeds controller you have need a voltage between, probably, 0 and 10 v to set motor speed.  However to confirm this you need to provide more than a photo, we need to have its specification or a link to one.

Second, you don't say how your PC is connected to the controller.  Assuming you have a breakout board, the PWM output from this is just a train of 5 volt (usually) pulses of varying mark/space ratio, which needs converting to the control voltage.  Again, we need to know details of the BoB to confirm this.  Unless it does the conversion internally you would need something between it and the controller to do it, it's only a simple circuit and several have been published.

Third, the PWM base frequency you have set is far too high by a factor of 100.  Something like 25 to 50 Hz is better to get smoother control.

Once you have this working the pulley ratio is irrelevant as your spindle doesn't have pulleys.

Please give us more information, on the breakout board type and controller type!


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Re: Help Please with PWM Spindle Motor Speed
« Reply #23 on: November 16, 2014, 05:16:02 PM »
Hello John and thank you so much for your reply. This is becoming a more of a quest or a mission to make this thing work properly, but at this point I am seriously thinking of ditching the Motor and Controller and either going back to the ‘Hanging Dolly’ and Flexi-Shaft or splashing out even more money on a different Spindle Motor set-up.

The kit came from (You guessed!) ‘Fleebay’ on http://www.ebay.co.uk/itm/400W-CNC-Spindle-Motor-Kits-PWM-Speed-Controller-400W-Motor-With-Mount-Bracket-/221360481671?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item338a1ce587

I must confess, the Motor is quite impressive, very quite at 6,000 to 8,000 RPM with very little run-out.

The specs on the PWM Controller are:
•   Support AC and DC input
•   DC Input : DC 15-160V
•   AC Input : 12-110V input
•   Support Current :10 A
•   PWM input : level 3.5-12V VPP
•   Frequency :1K-10KHZ(Particularly suitable for MACH3 spindle speed control.)

  The Breakout Board is what was supplied with the Mill, which I have modified to take opto-couplers for the limits, e-stops and a touch pad. Pin1 from the LPT port as in the drawing from a kind person on CNC Zone is fed directly to the Speed Controller.

The Power supply is a 48v 10A SMPSU with enough power to blow your hat off.

As I said in the very beginning, it works fine I just cannot get it to marry up with the spindle speeds on the DRO’s it’s not a matter of being out a 1,000RPM or so, it is running about 75 – 80% out.

I really appreciate any help that anyone can throw at me; I cannot believe I am the only ‘Muppet’ on the Planet to have bought one of these .

One slight caveat with the drawing I have posted is that if memory serves me the pulse train on the Pin 1 is negative going to where pin 2 on the ‘MOTO’ Port is High (5v) In the drawing Pin 2 goes to deck. 
« Last Edit: November 16, 2014, 05:23:52 PM by Buggalugs »
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Help Please with PWM Spindle Motor Speed
« Reply #24 on: November 16, 2014, 07:05:27 PM »
Ok, here are a couple of ideas.  First, let's assume that the controller wants to receive a PWM signal at its input at a frequency between 1 and 10 kHz, which is what the spec says.  If this is correct then the controller just uses that to switch the supply to the motor on and off with the varying mark/space ratio that Mach puts out, which should vary the motor speed in the expected way.  You have set the PWM base frequency to 2500 Hz which is in the range suggested.  Unfortunately the way that Mach works is that the mark/space ratio is derived from the kernel speed.  Supposing that the kernel speed is set to 25 kHz which is suggested in the manual, there are only 10 discrete pulse lengths of a  2.5 kHz signal that Mach can generate.  You would not therefore expect to see a very smoothly varying speed.  One way to check this would be to set the PWM base frequency to something very low, like say 2 Hz.  If the controller works in the way we are assuming, you will find that the motor runs very unevenly, as it will be starting and stopping twice a second.  IF the controller works in this way then it isn't really compatible with Mach.

So could I suggest that you try this test and report what you find.  Depending, we can think again about what to do.


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Re: Help Please with PWM Spindle Motor Speed
« Reply #25 on: November 17, 2014, 04:24:36 AM »
Thank you once again John for your help, it is greatly appreciated. I will try this out later today and get back to you.
 

I don't want to muddy the water any more at this stage, but after writing  my last post I did ponder about the PWM signal to the Speed Controller being inverted from the Breakout Board. I have a full set of Spare PCB's for the Mill's Electronics and I am going to ring through the 5v Line to the MOTO Connector to validate my statement that there is an error on the Drawing. My thinking is that if the Pulse train is Negative going and the Speed Controller is expecting a Positive going then that could explain why my findings are so erratic. (Y/N??) 

I'm not too sure what would happen if as I am thinking the PWM Pulse train was inverted, if it would indeed work at all.

Just thoughts of a desperate and demented individual..... ??? 
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Help Please with PWM Spindle Motor Speed
« Reply #26 on: November 17, 2014, 05:45:09 AM »
Well, if it was just inverted then you would expect the sense of the speed control to be inverted too.  So set it lowest and it would run highest and vice versa.  But if the BoB and controller have a common ground then you would just be grounding the controller input and nothing would happen.

By the way I see no drawing?


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Re: Help Please with PWM Spindle Motor Speed
« Reply #27 on: November 17, 2014, 08:15:27 AM »
Hello again John, The Schematic is attached at the bottom of my second last post as a schematic.pdf.

As a side element, can you recommend a Speed Controller that works with the Spindle Motor I purchased and with Mach3 ?
« Last Edit: November 17, 2014, 08:19:33 AM by Buggalugs »
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Re: Help Please with PWM Spindle Motor Speed
« Reply #28 on: November 18, 2014, 12:57:14 AM »
I see it!  I'm not sure what you meant by your comment in pin 2 and negative going.  Pin 2 on which connector?  I suggest we try to find out more about this speed controller first before looking for another one.  Suggest you try the test that I recommended.
Help Please with PWM Spindle Motor Speed
« Reply #29 on: November 18, 2014, 11:05:23 AM »
Well this is curiouser and curiouser!  There is an exactly similar unit on eBay with the item number 191239446164, but there it says that it uses a variable voltage drive and even supply a potentiometer  for manual control.  Did the supplier send any documentation with the unit?  I think either it has two modes, one in which it uses a variable voltage and the other where it accepts an external PWM pulse (possibly selected by that jumper on the pcb); or it is designed to accept only a variable voltage but the suppliers have tried driving it directly from Mach and found the only way to make it work is to use a high base frequency and hope the circuit does a bit of smoothing internally.  Unless we have some documentation or I can see the unit I don't know what to suggest.


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