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Author Topic: Mach3 Output For DC Motor Control  (Read 17267 times)

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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.
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.
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 »
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.
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
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).