When running Mach3 with a Kernel speed of 25kHz you can choose (more or less) any pulse repetition frequency for the PWM signal of between 5 Hz and 4 kHz.

Tweakie.

Found some light reading
http://www.cjh.com.au//PWM Spindle Control using Mach3.pdf
Noticed you have had a read at this before Tweakie

Excellent article by C.J.H. - explains the setting-up and operation of the Mach3 PWM very well.

Just out or curiosity Robert - what is the maximum and minimum RPM of your outrunners ?

Tweakie.

RPM is calculated by the voltage multiplied by the KVA of the Outrunner.
In my case I will be using 12.5 vdc
and a 890 KVA motor.
Giving me a max of 11,125 RPM
Not to sure where it starts out but I'm going to guess at about 500 but stalling is a problem at that kind of speed if trying to mill anything

Yes that is right!
Forgot that part lol

Attiny programmer made and ready to get this project running

Looks like you are well on your way with the speed controller project Robert.

Tweakie.

Not sure if I have any tiny13's left only 85's.
Are you thinking of using the internal clock ?
I have done some reading up but for a none programing guy like myself it's over dive on the nerd
Seems like there are many ways to skin this cat, software and hardware wise

I'm not sure but correct me if I'm wrong, how I see it since there are many different input voltage ranges I think a voltage divider circuit before the input would be a good idea.
It would be a little more work code wise but this way anything above 5vdc could be adjusted then calculated in code to convert to the proper ms output based on the input voltage.

In sence three or four diffent codes to work with the supplied input
Know your input volts
Adjust divider
Upload code for said divider setting

I agree.

It does seem a bit pointless to convert a digital signal to analog in hardware only to convert it back to digital again in software.

It would be a simple enough task to sample the Mach3 PWM waveform, measuring the width of a duty cycle pulse then scaling the value found into the 1 mS – 2 mS range then outputting this pulse - all done in a continuous loop repeating at a 20 mS interval.


Tweakie.

Hi Bit53b,

Thank you for the information and link (a chip that I didn't even know existed).

I think the processing power of the ATtiny and similar R.I.S.C. chips will allow an incoming PWM to be measured quite easily without having to resort to a specialist chip. Of course, the proof of the pudding is always in the eating, so it has yet to be proven but I have every confidence.

Tweakie.

Ok I must have miss understood something as I thought mach3 put out a 0-10 anolog signal
Now that I re-read things it's the G540 that puts out the 0-10 based on mach3s PWM signal that works with the chin VFDs.
So yes my idea is pointless

Something that may help but I hit a language block after a few links
http://digistump.com/board/index.php?topic=689.0

I

have all said parts needed to construct the circuit shown mind you it's a 85 not 45 but that really don't matter other then cost

Do you think a PC817 would also work in place of the 4n35, may not be fast enough :/

Hi Guys,

Having babbled on about it, I thought I would just have to give it a try - I had a bit of spare time so connected up a test rig yesterday afternoon.
I am using a spare pcb (made for another project), the Microchip PIC12f683 and TTL gates for I/O buffering.

For the initial tests I have set a Mach3 spindle range of 0 to 100 to indicate percentage of motor speed so 0% is off and 100% is full speed (GCodes: S0 to S100).

I don’t have a spare outrunner (without stripping down one of my models and that is not going to happen) but I am assuming that if we can control a servo then we can control a bldc controller in a similar manner.

For those that are interested, here is a short video; http://www.graytel.talktalk.net/bldcPWM.wmv


Tweakie.