Author Topic: Mach3 Output For DC Motor Control  (Read 16558 times)

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Offline PurpleThumb

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Re: Mach3 Output For DC Motor Control
« Reply #10 on: August 02, 2013, 12:12:58 PM »
Hi Tweakie,

I would be most happy to share my progress ( successes & failures ).

Thanks for Asking.

B.

"All of us together are smarter than any one of us"


Offline Tweakie.CNC

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Re: Mach3 Output For DC Motor Control
« Reply #11 on: August 02, 2013, 12:16:42 PM »
Quote
"All of us together are smarter than any one of us"

Absolutely true my friend  ;)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline JohnHaine

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Re: Mach3 Output For DC Motor Control
« Reply #12 on: August 04, 2013, 03:07:34 AM »
To answer your original question, the answer is that the PWM base frequency that Mach outputs is quite low. See section 5.5.5.2 of the config guide which mentions a value of 50 Hz.  But I am sure I have seen posts where people are using even lower, down to 20 Hz.  So smoothing the signal with an RC and applying the resulting signal to a conventional motor control makes more sense perhaps to give smooth running.  If you try the direct drive it would be interesting to know the results.

Offline PurpleThumb

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Re: Mach3 Output For DC Motor Control
« Reply #13 on: August 04, 2013, 09:43:44 AM »
Hi Tweakie

I think that 50hz base frequency may be unusable, as I understand most systems use 10K or more.

I'm hoping that the base frequency is configurable in Mach3, see below...



I would like to construct a spindle motor speed control driver that will also operate stand alone, so I would'nt have to boot
the computer and launch Mach3, just to drill a hole. Also maybe a foot operated foot switch to reverse the spindle, for tapping threads...

Funny how these projects tend to sometimes expand on their own...

Cheers!

Bill
« Last Edit: August 04, 2013, 09:49:12 AM by PurpleThumb »

Offline HimyKabibble

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Re: Mach3 Output For DC Motor Control
« Reply #14 on: August 04, 2013, 09:49:46 AM »
The PWM outputs, like all Mach3 outputs when using the PP, are limited by the kernel frequency.  The higher the output frequency, the less resolution you get.  With a 25kHz kernel, and 10kHz PWM frequency, you'd have less than 2 bits of resolution.  Some hardware motion controllers, like SmoothStepper, will allow higher frequencies, but I'd be surprised if even they supported 10 kHz.

Regards,
Ray L.
Regards,
Ray L.

Offline PurpleThumb

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Re: Mach3 Output For DC Motor Control
« Reply #15 on: August 04, 2013, 10:07:03 AM »
Hi Ray,

I understand.

Could be the reason why no one ( as far as I know ) drives directly from Mach3.

I wonder what the lowest usable base frequency is?

What are the drawbacks of a low base frequency? Noise? Choppy Operation?

Don't know.

Thanks for posting,

Bill

Offline JohnHaine

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Re: Mach3 Output For DC Motor Control
« Reply #16 on: August 04, 2013, 05:40:15 PM »
Both of those.  And if you want to be independent of Mach for the odd hole then a standard motor controller makes sense.  It only needs an R and a C to smooth the PWM output, and maybe an op amp.  I use a KB motor controller and they are excellent ( though haven't got Mach controlling it yet).