Messages

1641

Mach4 General Discussion / Re: Slow stepper speeds

« on: March 13, 2020, 08:18:04 PM »

Hi,
I agree with Steve, use the highest voltage power supply your divers will tolerate. Geckos have a superb reputation for
reliability, if they say 80V...then use 80V.

What model steppers do you have? In particular do you know the inductance? It is a little understood fact that the inductance
of a stepper determines how badly the torque will degrade with stepper speed.

Most stepper manufacturers make high holding torque (desirable) steppers but with commensurately high inductance (highly
undesirable) because they can make them cheaply and thereby appeal to first time buyers.

If you absolutely require the fastest possible axis speed then you will probably have to replace your steppers with the
LOWEST POSSIBLE inductance. This might mean that a (say) 300 oz.in stepper of 1mH inductance is a better choice
than a 600Oz.in stepper but 6.8mH because the smaller stepper will still have useful torque at 1000rpm whereas the bigger
one stalled at 300 rpm.

Craig

1642

Mach4 General Discussion / Re: Mesa FPGA cards

« on: March 13, 2020, 07:37:34 PM »

Hi,

Just out of curiosity would the use of windows embedded instead of the regular windows versions offer a performance increase or is it just a stripped down version that is still not real time capable.

I use Windows 7 Embedded (Standard) on my machine PC. Windows Embedded allow you to load, or not load chunks of code. For instance
you have no need of multimedia capabilities when designing and building a Point of Sale PC so why bother loading it?.

I would recommend 'The Professionals Guide to Windows Embedded Standard 7 by Sean Liming', Chapter 8 'Realtime Support'
and the references contained therein do a masterly job of explaining why Windows is unsuited to realtime use.

The essential idea is that 'Windows Embedded does not  change Windows essential DNA'. Windows makes HUGELY EXTENSIVE
use of the CPU's interrupt system, it uses it to schedule threads and all manner of things in a multilevel priority scheme.
You can't turn them off nor can you (materially) alter the priority WITHOUT crashing Windows.

Thus when an app like Mach4 demands service it must always defer to higher priority tasks determined by Windows, to do otherwise
is to crash it. Therefore Mach (3 or 4), and in fact ALL Windows PC based CNC software solutions, must have a buffer so that
when Windows skives off to do some important (to Windows) task meaning Mach4 is paused the buffer allows the motion controller
a queue of motion data to consume. We just have to hope the Mach4 again receives CPU service BEFORE the motion buffer is drained
otherwise you motion controller 'runs out of data' and the machine stops.

You might think that this fundamental difference between realtime (example: LinuxCNC) and buffered (example: Mach4) puts
the Windows solutions at a disadvantage. There is a modicum of truth to that.

However when you are standing at the machine operating it there is virtually NO DESCERNABLE difference between them.
One time that you might notice a difference is if you hit <FeedHold>, with Mach the machine will continue to operate for the duration
of the buffer, commonly around 200ms, whereas LinuxCNC would stop, to all intents and purposes, instantly.

The other time  where LinuxCNC shines is the ability of the software to enact closed loop control over servos whereas Mach4 cannot do so
directly. Having said that you may have noticed a recent development in AC servo technology called 'dual sensing'.
For example Delta A2 series servos. The servo drive monitors the servo mounted encoder as all  servos drives must do but can in
addition monitor a second encoder, like a linear scale, and incorporate that into its position loop as well. Thus my Mach4/ESS solution
could now enclose a linear scale 'just like the realtime boys' by use of such a servo and drive. They cost about $50 more than
the regular B2 series (160,000 count encoder) servos I have just bought! Ho hum, I wish I'd done a little more research before I
bought them....not that I need dual sensing....its just I want to brag....and do what my mother recommended I did not for the sake of
my eyesight! LOL

Craig

1643

Mach4 General Discussion / Re: Mesa FPGA cards

« on: March 13, 2020, 06:23:38 PM »

Hi,

There used to be a beast called Windows RT, but as best I know it no longer exists.

There is still such a beast, I don't know about RT, its been a long time since I've seen any reference to it, but there is
Interval Zero.

They have some superb videos on their website about how they enact realtime processing on a Windows PC, highly
recommended.

The idea is that one core of a multicore processor runs a realtime scheduler while the rest of the cores runs Windows normally.
There is a rather slick data exchange between the realtime thread and Windows but at no time can Windows interfere or stop the
realtime thread.

I investigated purchasing it some years ago, it was going to cost $16000AUD for the software tools and then there is still
the per machine runtime license. The price stooped me cold!

In recent times Interval Zero have partnered with Kingstar and they have used the realitme core to enact EtherCat, a realtime
Ethernet communication protocol that works with Mach4. This is to my knowledge, the fisrt attempt anyone has  made to
'make Windows realtime' and thence use it as a CNC solution.

Note this idea of a realtime core does not make Mach4 suddenly realtime, Mach4 is still a Windows app and requires a Winodws
environment replete with the scheduling delays that characterize Windows. What a realtime core can do how ever is run a
smaller realtime program like EtherCat. All very clever!!!

Smurph seemed very impressed with the ease of which the Interval Zero realtime core could be grafted into an existing
Windows PC. The video banner of this forum is of a Matsurra VMC making a part running Mach4/EtherCat by Kingstar/Interval Zero.

It has rather taken us adrift from OP's question regarding the suitability of Mach4 for realtime closed loop control of
servos, then answer is no.



Craig

1644

Mach4 General Discussion / Re: Mesa FPGA cards

« on: March 13, 2020, 05:05:34 PM »

Hi,

Command and control messages are outside of the PVT queue and I was implying that the servo loop correction would operate through command and control messages, not the Mach4 PVT queue.

Good point, and is this just exactly what NFS has exploited to enact software controlled THC released some months ago? Using
the concept of an override axis a servo/stepper can be adjusted in near realtime 'around' its nominal trajectory be offered up by
the motion buffer. The apparent bandwidth of that setup is about 10Hz-20Hz and is adequate for all but the most demanding
(dynamically speaking) THC loops but is still a factor of five short of the bandwidth required for effective servo control.

Ideally the motion control would have a processor capable of closing the loop inside the motion control, but as far as I know, only the Vital Systems Hicon family and the CS Labs CSMIO/A offer closed loop within the motion controller.

Yes, I would agree. This was my intent to inform OP that Mach4, not withstanding the much improved command/control loop frequency,
is not suitable as a positional feedback controller. That capability would have to be provided by the FPGA on the Mesa board.
I'm unfamiliar with those boards but was not aware that they had feedback capability.

Craig

1645

General Mach Discussion / Re: Question on Novum V2 BOB

« on: March 13, 2020, 04:45:38 PM »

Hi,
if you have bought a genuine Mach3 license I would suggest send tweakie a PM, he may relent.
The reason that the company is blacklisted is because they routinely peddle pirate Mach3 licenses.
The expectation that you are going to get help on the forum funded by the company (NFS) who are being
ripped off by Novum is not realistic.

Do yourself a favor and buy a decent controller, a US or European made one. I personally recommend an Ethernet SmoothStepper
but others will equally recommend any of the UC100, UC300, UC400 series by CNCDrive or 57CNC by PoKeys.
Chinese controllers seldom work as advertised and you'll find that if you want help China might as well be in another galaxy,
they just don't seem to care about their prey, sorry, customers once they have bought their board.

Craig

1646

Mach4 General Discussion / Re: Mesa FPGA cards

« on: March 13, 2020, 04:28:24 PM »

Hi,

I think the depth of the motion queue does not delay command and control messages

Motion commands are issued by the trajectory planner in the form of PVT data which is queued. Even if Mach was instantly
updated by Ethernet about the position of the servo it would still have to issue trajectory commands and ergo the buffering
delay.

Closed loop control bandwidth is highly dependent on the 'around the loop' communication delay. If you have a buffering
delay of 100ms, given the Nyquist sampling theorem, the best possible closed loop bandwidth would be 5 Hz. Any control
engineer will tell you that the discrimination of a control loop running at the Nyquist frequency is rubbish, you will get
only fair discrimination at 1/10^th the Nyquist rate, in our example 0.5Hz.

Half a Hz bandwidth might be adequate for a temperature control loop with a temperature time constant of 5 seconds but
it will fail miserably trying to control a servo.

Adequate servo control for CNC axis purposes requires an absolute minimum position bandwidth of 100Hz, 250 to 500Hz is
the common norm for entry level servos and 1000 to 5000Hz  for the latest and greatest servos.

Mach4 is not a realtime control system, and that is because the operating system on which it runs (Windows) is not realtime
capable.

Linux distros with R(eal) T(ime) E(xentsions) is realtime with a quite respectable jitter of 2us-4us on common PC hardware.
Windows can't manage that.

Craig

1647

Mach4 General Discussion / Re: Mesa FPGA cards

« on: March 13, 2020, 03:38:55 PM »

Hi,

or in the software of the Mach4 plug-in running on  the computer. Using the plug-in software would likely be the easier approach.

Really? What about the buffering delay between Mach4 and the motion controller? The ESS has a default setting of 180ms buffer.
All Mach4 controllers require a buffer. You cannot close loop control a servo with that sort of delay.

It is certainly possible for the FPGA to present Mach4 with the current encoder count for a DRO for instance, but that is not closed loop
control.

Craig

1648

General Mach Discussion / Re: New to DIY cnc , Looking for some guidance and advice on first CNC

« on: March 13, 2020, 03:28:09 PM »

Hi,
if this is a new build then I would recommend Mach4. All development on Mach3 ceased six years ago, if you are going
to invest several thousand dollars on machine hardware it doesn't make sense to use obsolete software.

I use an Ethernet SmoothStepper by Warp9. It has arguably the best and most complete Mach4 plugin and realtime
features of any of the Mach4 controllers.

I use two single port bi-directional breakout boards. They have no opto-isolation, relays nor PWM outputs, I add those
features as I require. This results in best flexibility and lowest cost but requires you be prepared to make a few
simple electronic additions to the boards.

If you prefer a 'ready to rock and roll' breakout board with all three ESS ports fully developed then the MB03 by
CNCRoom is recommended.

Craig

1649

Mach4 General Discussion / Re: Mesa FPGA cards

« on: March 13, 2020, 01:12:49 AM »

Hi,

So I hope that Mach4 is able to handle the closed loop signals from the linear encoders.

No, Mach4 is not a feedback  controller because it is buffered. That is to say that Mach4 is not realtime and must therefore buffer motion commands and as a consequence the 'around the loop delay' precludes realtime feedback.

Those devices that do offer feedback control to Mach4 (Hicon suitably activated and CSMIO/A) the feedback loop is handled by the
motion controller with realtime hardware under the supervision of Mach.

If you wish to have realtime linear encoder feedback YOU MUUST enact it within the FPGA of the Mesa board.

Craig

1650

Mach4 General Discussion / Re: Mesa FPGA cards

« on: March 13, 2020, 01:11:14 AM »

Hi,
sounds like a great project.

Craig