# Machsupport Forum

## Mach Discussion => General Mach Discussion => Topic started by: bill-the-cat on May 31, 2009, 06:58:46 PM

Title: Pulse Frequency
Post by: bill-the-cat on May 31, 2009, 06:58:46 PM
I've just completed the video tutloriials, so I'm really new here.

I'm curious about the Pulse Frequency setting in Mach 3.  All the tutorial said was that you should set it at 25,000.  Why are there higher values?  When would you want to increase this setting?

I'm one of those people that just can't settle for "just do this" without knowing the why.

Thanks!
Title: Re: Pulse Frequency
Post by: Chip on May 31, 2009, 07:43:13 PM
Hi, Bill

In short you don't need to increase the pulse frequency unless you max out your motor tuning velocity values.

If your steps per values are below 10,000 per unit, 25 K should be fine for now, It will all make sense in a while.

Chip
Title: Re: Pulse Frequency
Post by: bill-the-cat on June 01, 2009, 09:19:30 AM
Thanks for the quick response Chip!

My steps/unit is (are?) 40,000, if I calculated it correctly. (200 motor steps/rev X 10 driver micro-steps/step X 20 TPI Lead Screw).

Your could just tell me if 25,000 is still a good setting for Pulse Frequency, or what setting I should use.

However,  instead of just telling me what value to use, I'd rather get more insight into exactly how the Pulse Frequency setting relates to the overall configuration of Mach 3. That way I can understand the implications of this setting and answer my own question.

"Give a man a fish and he eats for a day.  Teach a man to fish and he eats for a lifetime."
Title: Re: Pulse Frequency
Post by: HimyKabibble on June 01, 2009, 11:05:01 AM
Bill,

The pulse frequency is the maximum step rate Mach can generate.  If your machine has 2000 steps/inch, and you want to run 100 IPM rapids, you need a step rate of 2000 * 100 / 60 = 3333Hz.  So, 25kHz is more than plenty.  However, if you have a machine like mine, which has 20000 steps/inch, and want to run 100 IPM rapids, you'd need 20000 * 100 / 60 = 33,333 steps/inch, so you'd need to increase the pulse rate.  Most modern PCs will handle 45kHz pulse rate, some will go higher.  If you need higher still, the SmoothStepper will go up to 4MHz.  In general, you want to run the lowest pulse rate that meets your needs, to keep from just wasting a lot of CPU power on the PC.  There is no advantage to running faster than required.

Regards,
Ray L.
Title: Re: Pulse Frequency
Post by: bill-the-cat on June 01, 2009, 03:29:28 PM
Thanks Ray! That's the answer I was looking for  ;D

One more question.  You say "most modern PC's will handle 45kHz pulse rate". How do I know what MY PC will handle?  Will I just get bad results from the driver test if I try to go too high?
Title: Re: Pulse Frequency
Post by: HimyKabibble on June 01, 2009, 03:43:39 PM
Thanks Ray! That's the answer I was looking for  ;D

One more question.  You say "most modern PC's will handle 45kHz pulse rate". How do I know what MY PC will handle?  Will I just get bad results from the driver test if I try to go too high?

Bill,

Yup, driver test is the only way to know, and even that may not be 100%.  If driver test says it's OK, try it.  If you have wierd problems, back off and see if they go away.

Regards,
Ray L.
Title: Re: Pulse Frequency
Post by: Chris.Botha on June 01, 2009, 05:29:02 PM
I have 0.9 degree stepper so 400(steps) x 10(tpi) x 10(Microsteps) = 40000 Steps per inch or 1574.8031496 steps per mm.

I want to run at 1200mm/min or in your funky American talk 47.244 IPM

As I calculate it I need to have

40000 * 47.244 / 60 = 31496hz...

so I set at 36000hz? no point in going to 45000hz?

Title: Re: Pulse Frequency
Post by: Chris.Botha on June 01, 2009, 05:38:40 PM
PS. my little dell optiplex 3.2 HT box with 1gb of ram runs driver test fine all the way thru to 100 000HZ.. at 100 000 i go from "system excellent" to "stable" intermittently.

BUT..

at 24000hz cutting at 600mm/min (23.622IPM) my mach freaks out or my mill does and throws away moves when my fourth axis rotates to cut the opposite side of a flip cut. The rotation will be incomplete or of Y by up to 20mm and then continue cutting.

I can cancel out this problem by killing the toolpath display window.. to some extent (thanks ken for tip) but it occurs to me that mach should have ample grunt to update the toolpath display and still be sending out a simple A rotation sequence?

possible my motor tuning is wrong for A axis?? if so why would turning off  toolpath display help?

  this only happens with larger paths. 15mb or more

Title: Re: Pulse Frequency
Post by: Chip on June 01, 2009, 05:53:23 PM
Hi, Bill

Try referring to the manual, It's under Support above.

" **** 5.2.2 Defining engine frequency

The Mach3 driver can work at a frequency of 25,000 Hz (pulses per second), 35,000 Hz or
45,000 Hz depending on the speed of your processor and other loads placed on it when
running Mach3.
The frequency you need depends on the maximum pulse rate you need to drive any axis at
its top speed. 25,000 Hz will probably be suitable for stepper motor systems. With a 10
micro-step driver like a Gecko 201, you will get around 750 RPM from a standard 1.8o
stepper motor. High pulse rates are needed for servo drives that have high resolution shaft
encoders on the motor. Further details are given in the section on motor tuning.
Computers with a 1 GHz clock speed will almost certainly run at 35,000 Hz so you can
choose this if you need a higher step rate (e.g. if you have very fine pitch lead screws).

******************************************************************************************

The demonstration version will only run at 25,000 Hz. In addition if Mach3 is forcibly

closed then on re-start it will automatically revert to 25,000 Hz operation.

******************************************************************************************

The actual
frequency in the running system is displayed on the standard Diagnostics screen.
Don't forget to click the Apply button before proceeding. ***** "

Good Luck, Chip
Title: Re: Pulse Frequency
Post by: bill-the-cat on June 01, 2009, 06:18:40 PM
Thanks for the manual reference Chip!  I read through that llong before I actually got the software up and running.  I guess it didn't mean anything to me at the time and I didn't remember it when I needed it.

I honestly try to answer my own questions before I come on here and ask.  Guess I just had a senior moment on this one ;)
Title: Re: Pulse Frequency
Post by: Chip on June 01, 2009, 06:27:17 PM
Hi, Chris

It could be several things, Is your Pulse Frequency locked in solid all the time ?, Try setting your Step & Dir Pulses to 5 in Motor Tuning may help (It will give Your Control more time to see the pulses from Mach), Post your xml it may show some other issues that could cause it also.

Are you losing steps in Y and A only. ?

Chip
Title: Re: Pulse Frequency
Post by: Chris.Botha on June 01, 2009, 08:20:58 PM
at work right now.. will post my settings in my evening.. (+-7hrs from now)

pretty sure my step and dir pulses are set at 2 each..

the error does not present in Y.. what happens as best as i can guess is that there is some "lag" and the first thing that moves after my A has rotated is my Y to bring it back over the centre of my model.. i think in this time mach is playing catch up or summing and the loss of steps to A carries thru to Y.. by the time i start cutting X its sorted. (but A angle is out as well as Y.) (the cut itself then carries on cutting properly in X and Y but just in wrong position)

peculiar error.. goes away if i switch off toolpath display.. and only on big paths.. think its more related to processor speed perhaps. i have not had time to test it at a changed kernel speed, but if all the previous posts are anything to go by then upping kernel speed will make this problem worse not better as higher kernel speed puts more load on processor.

notable here too..

pure rotary jobs, (which are typically my heaviest gcode jobs) cut fine, with toolpath display on.. very strangle.. it seems like it only does it when i instruct rotary to turn from a0 to a180 in one movement at 600mm/min..

will post xml in later :)

Title: Re: Pulse Frequency
Post by: Chris.Botha on June 01, 2009, 08:39:24 PM
ok my wife sent my xml to me..

man.. the value of a wife that can find your mach xml for you is under rated..

here it is..

this is my backup xml at 24000hz

edit (added set file that xml calls)
Title: Re: Pulse Frequency
Post by: Chip on June 01, 2009, 09:10:14 PM
Hi, Chris

Try setting the A axis step low active the same as all the rest "Checked", They should all be the same, Some controls are sensitive to this.

If it's a different type of control for "A" they may need to be "X" for step & dir Low actives settings.

Chip
Title: Re: Pulse Frequency
Post by: Chris.Botha on June 01, 2009, 09:18:38 PM
not sure why that one is different.. i dont poke around in there usually. those are defaults from my mach install i think. will try changing that and give it a whirl.

far as i know all the steppers are the same make and brand as well as the controllers for them so you are right.. should be the same i guess?
Title: Re: Pulse Frequency
Post by: Chris.Botha on June 01, 2009, 10:02:24 PM
ok got news from a fellow user.. apparently if i switch A low active on all my lettering  on jewellery will come out reversed/mirrored, think he means will turn in wrong direction for milling. ??

Title: Re: Pulse Frequency
Post by: Chip on June 01, 2009, 10:32:02 PM
Hi, Chris

Only the "Direction" Low Active will do that in ports & pins, If the control's are all the same then all low actives dir & step should be the same all way's.

Home & Limit's, "Reversed" is used to Reverse an Axis when Needed, Or you need to change motor wiring.

Chip
Title: Re: Pulse Frequency
Post by: Chris.Botha on June 01, 2009, 10:34:01 PM
ok cool will test that tonight :)

thanks for help.. like i said before not a major issue.. resolves by turning off toolpath display but would like to get it all running if i can :)
Title: Re: Pulse Frequency
Post by: Chris.Botha on June 02, 2009, 03:05:52 AM
well.. tie me up and tickle me with a dwarf...

did not change anything when i got home tonight.. only changes made were to my motor tuning to up the x,y,z to 1200mm/min and kernel to 35000. did not change that other setting either.

"A" seems fine now.. could not find a path that stalled it on a 180 flip. will continue testing, will also take it back to 24000 to see if its the kernel speed that made difference but everything in me says its not that.

will probably only happen to me when i have a paying job on the mill..!!  typically!

If that hapens again i will document it. I know other people with exactly same mill and setting have the same issue so im reasonably sure its not just a figment of my imagination ;)
Title: Re: Pulse Frequency
Post by: Chip on June 02, 2009, 03:18:33 AM
Hi, Chris

Sounds like the luck I have hear, Been chasing my tail for awhile also.

Chip
Title: Re: Pulse Frequency
Post by: Chris.Botha on June 02, 2009, 03:23:20 AM
well thanks for your time in helping me dude.. appreciated :)

no time right now to chase this one but have to cut a super dense part tomorrow night.. i think if its gonna freak it would be then.

Title: Re: Pulse Frequency
Post by: Chris.Botha on June 02, 2009, 07:29:33 AM
didnt solve that issue but kernel stepping solved.

uploaded this vid of probes for a mate.

small success but its a start in the right direction

Title: Re: Pulse Frequency
Post by: Chris.Botha on June 02, 2009, 05:08:26 PM
posted on 3dcadjewelery re this issue and got this response  (some few other jewellers have had same issue it seems, and all solve it by switching off toolpath display.

Quote
I have had this issue before! and yes, turning off the display window solves it.

But lets break it down a bit. nd I will give you WHY its doing it........

X Y and Z have a ratio of 10 to 1 (without the microstepping) so at a given speed in motor tuning, the stepper motor has to rotate at a certain RPM to reach your motor tuning speed. So to rotate that certain speed, the computer has to put out so many pulses.

The A axis gearing is MUCH MUCH higher. 72 t0 1 I believe. So the computer has to put out alot more pulses to reach the motor tuning speed. It is hogging processor power. And believe it or not there is quite a bit of processor power needed to also rotate the model in the toolpath screen. I have a p4 2.8 with 2 gigs of ram, and I still get that on large files.

any clues?

Title: Re: Pulse Frequency
Post by: Chris.Botha on June 02, 2009, 05:48:30 PM
im prepared to live with this "error" if its simply a case of processing power.. only chasing it in case its a simple tickbox correction somewhere :)
Title: Re: Pulse Frequency
Post by: Hood on June 03, 2009, 02:48:52 AM
It is likely to be  CPU/Graphics issue, at the moment the way Mach uses the toolpath takes a lot out of Mach but in the next revision this has all changed and the toolpath is entirely seperate and will probably help in your situation.
Hood
Title: Re: Pulse Frequency
Post by: Chris.Botha on June 03, 2009, 03:37:57 AM
cool.. thanks guys...