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  1. #1
    Join Date
    Mar 2008
    Posts
    108

    What do you think of EMC?

    Hello all, I am considering using EMC to controll my Bridgeport. I am going to be doing a PC based software conversion to replace my old DOS controller. I was going to use Mach3 but have recently been told that my servo drives need PWM inputs and that Mach only has step and direction outputs. I was planning on using a Pico systems controller that uses PWM and John from Pico says his board works perfectly with EMC. I don't have any Linux experience at all, never used it. How do you like EMC? What are the pros and cons of the software? If you have used Mach3 and EMC, which do you like better? Is it user friendly?

    Thanks.
    Scott

  2. #2
    Join Date
    Feb 2007
    Posts
    592

    EMC?

    Scott;

    I admit I'm a computer geek and Linux is just another O/S to me.

    But:

    Get yourself a copy of the latest EMC2 Live CD - Don't even install it. Just boot to it and play with some of the SIM configs.

    Actually Installing is almost as easy. The Live CD can do a Ubuntu Linux install with the EMC program allready setup in basic configs. The Pico Systems hardware drivers are allready in the EMC bundle.

    Help is almost always available on the #EMC irc.

    Try it, I think you will like it.

  3. #3
    Join Date
    Jul 2005
    Posts
    82
    I've only ever used EMC to drive my machine, I love it, granted however I know nothing else. I recently purchased some equipment from pico systems (john) but have yet to use it, i'm building a new cnc machine and once it's done it'll be using the pico systems universal stepper controller.

    EMC has always worked great for me though, no software failures (my cnc machine has screwed up before eheh, but that's my fault).

    Ross

  4. #4
    Join Date
    May 2005
    Posts
    1662
    Quote Originally Posted by NJC View Post
    I was planning on using a Pico systems controller that uses PWM and John from Pico says his board works perfectly with EMC.
    If you go this route you're married to emc afaik.

    How do you like EMC?
    Very much. Emc users are relatively small in numbers but large in enthusiasm.

    What are the pros and cons of the software?
    If you are used to a big brand CNC the control in emc can be a bit clumsy. Not sure if Mach fares much better in this type of comparison.

    emc is much more than mill/lathe software. Most of us have only scratched the surface of it's capabilities as a machine control.

    If you have used Mach3 and EMC, which do you like better?
    Limited Mach experience. As a motion control it may be a sawoff. Realtime kernel has a theororetical advantage.

    Compared to to Mach there is less documentation and fewer wizards. This gap is closing somewhat.

    Is it user friendly?
    If this is your first experience with *nix there is a learning curve. Ubuntu eases the transition a great deal.

    Old linux joke: Linux is user friendly, it's just particular who it chooses for friends.
    Don't let this scare you off
    Anyone who says "It only goes together one way" has no imagination.

  5. #5
    Join Date
    Feb 2007
    Posts
    514
    I used EMC on my plasma table and it is highly configurable. Some of the documents are a bit terse but the irc and mailing list is full of helpful people when you hit a snag.

    Pros
    It is open source
    It is real time
    It is configurable
    It is being improved every day
    It cost you nothing but some time to try it out

    Cons
    The docs are lacking
    It won't work on a laptop afaik

    Linux can take a bit to get use to if your a seasoned window user but, Unbuntu makes it as easy as possible...

    Oh, yes don't forget the wiki site it is full of info...

    John

  6. #6
    Join Date
    Mar 2008
    Posts
    108
    Well, sounds like you all are happy with it, I was hoping to hear that. Sounds like the technical part of the software is very well thought out and works well. Maybe Mach has more bells and whistles, like the wizards. I was told that EMC allows use of the machine manually as well as with the controller and that Mach doesn't allow one to use it manually, is this true? Would be nice to be able to do simple tasks quickly without programming. I'm used to setting up my work now manually, I don't have a thumbwheel or anything like that, it's a real simple system, I kinda like it that way.

    Thanks for all the unput!

    Scott

  7. #7
    Join Date
    Apr 2003
    Posts
    307
    Let's not forget about the fact that you don't need a super computer to run EMC2. I'm using it on a 650 mhz PIII. Well maybe a little faster would be better for the GUI. But Ubuntu Linux and EMC get along fine on simpler machines. Check the recommended hardware list.
    EMC Wiki Hardware Requirements

    Chris

  8. #8
    Join Date
    Apr 2005
    Posts
    263
    for generating PWM output there is also the Pluto-P which connects to the parallel port and the M5i20, a PCI card, so you might want to consider these too.

    my machine is not a bridgeport but it uses DC-servos, pwm amplifiers from Jon Elson, and an m5i20 + EMC2 to control it all. Videos here:
    http://www.cnczone.com/forums/forumdisplay.php?f=386

    You mentioned manual machining. If you leave the handwheels on the mill you can use EMC2 or make a custom program to use your computer as a DRO - only displays coordinates no cnc control.

  9. #9
    Join Date
    Dec 2003
    Posts
    24216
    Has anyone got PC Motion Control Cards to work in EMC?
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  10. #10
    Join Date
    Jul 2003
    Posts
    1753
    You have asked this a few times.. Maybe I need to ask - why do you think emc needs to support motion control cards? (really - I don't see a need). Emc2 does motion within itself. Any hardware that moves motion outside of emc isn't a good match. It would make emc2 not emc2 . Emc2 only requires 'dumb' cards that count encoders and maybe a few dac's, adc's or PWM if your build requires that. Emc closes the pid loop within software.

    I love this quote from one of the emc2 developers
    Again - this goes back to emc2 being the motion controller. Equipment that moves the motion outside of emc isn't a good match. EMC is a closed-loop motion controller, unlike anything else that's affordable by hobbyists. Steppers only work because EMC fakes itself out with a made-up position value for the loop control.
    I don't have experience with gali or such - is there anything that it does that emc doesn't? Price wise - how do they compare to emc supported hardware? 4/8 axis card from mesa with +/- 10v 4 axis card and 2 24 i/o isolation boards costs around 199+69X3=$406. this gives you 4 axis + 32in 16out. You can look at other hardware here.
    http://wiki.linuxcnc.org/cgi-bin/emc...orted_Hardware

    pico systems has some nice cards also.

    (still - low budget you could even run PWM out the printer port and read encoders back in)

    sam



    Quote Originally Posted by Al_The_Man View Post
    Has anyone got PC Motion Control Cards to work in EMC?
    Al.

  11. #11
    Join Date
    Dec 2003
    Posts
    24216
    Quote Originally Posted by samco View Post
    You have asked this a few times.. Maybe I need to ask - why do you think emc needs to support motion control cards?
    I have asked it a few times and have received mixed inconclusive answers.
    May it is because I am not fully aware as to how EMC closes the loop?
    If it is closed withing the EMC s/w, then I would have though it wuld have been open to other forms of servo drive control such as 10v analogue?
    Also Does it support master/slave gearing and electronic cam etc?
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  12. #12
    Join Date
    Feb 2007
    Posts
    592

    Cool EMC supported hardware.

    Actually analog +/- 10V hardware is one of the best matches for EMC and can be implemented a number of different ways.

    Step/Dir type servo drives which treat a servo like a high priced stepper drive are supported but waste much of EMC's capability.

    Velocity mode (vrs steps) can run on a pIII-600 with marginal CPU loading - Try that on a Mach 3 based system.

    Likewise EMC preferably homes using an Index (aka Z channel) - so E-Stop or powering a machine down doesn't require reseting all your offsets.

    Emc also supports rigid tapping and being open source is constantly having new features added.

    Often EMC may not support something because no one has yet had the need for a function, but things get added as needed.

    A good example is 5 axis tool offsets...

    Check out Stuart's Cinnci - [ame="http://youtube.com/watch?v=mxxdq6y8z8M"]http://youtube.com/watch?v=mxxdq6y8z8M[/ame]

  13. #13
    Join Date
    Feb 2008
    Posts
    644
    Quote Originally Posted by Al_The_Man View Post
    I have asked it a few times and have received mixed inconclusive answers.
    May it is because I am not fully aware as to how EMC closes the loop?
    If it is closed withing the EMC s/w, then I would have though it wuld have been open to other forms of servo drive control such as 10v analogue?
    Also Does it support master/slave gearing and electronic cam etc?
    Al.
    In the servo case EMC closes the loop by reading actual position, comparing it with the desired position and outputing a control signal to the drive system to minimize the difference. The exact drive signal applied is calculated via a standard PID loop, just as in a 'smart' controller card.

    The position input to EMC is typically done via quadrature, and the output signal is typically PWM or analog +-10.

    EMC can do this with nothing more than a parallel port, with some encoder count speed and PWM resolution limitations. With decent hardware (Mesa. Pico, STG or Vital). EMCs servo performance is just as good as controllers that close the loop on the card, and has the advantage that all of the PID loop is in one place (and in the open). One reason this works as well as it does its that EMC runs under a true RTOS. 'Smart' controller cards are required by non-RTOS systems for decent performance, but not by EMC.

    Peter Wallace

  14. #14
    i came across this the other day and found it very interesting deffinitely makes emc a plus http://wiki.linuxcnc.org/cgi-bin/emc..._With_Encoders

    mach can t do this from what i understand
    A poet knows no boundary yet he is bound to the boundaries of ones own mind !! ........

  15. #15
    Join Date
    May 2006
    Posts
    2420
    Quote Originally Posted by NJC View Post
    Hello all, I am considering using EMC to controll my Bridgeport. I am going to be doing a PC based software conversion to replace my old DOS controller. I was going to use Mach3 but have recently been told that my servo drives need PWM inputs and that Mach only has step and direction outputs.
    Just a thought, by PWM do you mean quadrature or wave drive as it is called in Mach ?

    Or are you talking something like locked antiphase or sign/magnitude?

    If it is quadrature you need for your servo drives then I think the wave nc option in Mach will work with your drives directly, I am going to try this at some time, haven't quite got there yet.

    Having said that I would think that EMC would output a quadrature signal as well...not sure about that, someone more knowledgable of EMC may want to comment.

    Russell.

  16. #16
    Join Date
    Feb 2007
    Posts
    592
    Quote Originally Posted by epineh View Post
    Just a thought, by PWM do you mean quadrature or wave drive as it is called in Mach ?

    Or are you talking something like locked antiphase or sign/magnitude?

    If it is quadrature you need for your servo drives then I think the wave nc option in Mach will work with your drives directly, I am going to try this at some time, haven't quite got there yet.

    Having said that I would think that EMC would output a quadrature signal as well...not sure about that, someone more knowledgable of EMC may want to comment.

    Russell.
    Quadrature is an INPUT signal read from the position encoders...

    Some stepper drives are driven using the winding step phases.

  17. #17
    Join Date
    May 2006
    Posts
    2420
    Quote Originally Posted by skullworks View Post
    Quadrature is an INPUT signal read from the position encoders...

    Some stepper drives are driven using the winding step phases.
    It can also be used as an OUTPUT from PC to servo drive as in the case of the DSPIC servo drive which has a quadrature input from the controlling PC instead of step/dir, it also has quadrature input from the encoders.

  18. #18
    Join Date
    Feb 2007
    Posts
    592
    Quad from a PC to servo drive is a form of step/dir. 'A' leading 'B' or 'A' trailing 'B' defines direction, and total counts define the move distance.

    When Quad is only fed back to the servo drive from the motors (IE Gecko 320's) Then the system is semi open loop as the PC only knows that it has not received an error from the amp and that the servo is "somewhere" within the +/- 128 encoder counts it takes to fault the amp for a following error. Depending on screw pitch and encoder counts per revolution this error could be huge.

    There are "BOB" 's that share encoder info with the PC but those are and exception to the rule for "hobby" type setups.

    EMC comes from the other end, intended to replace controls on big iron if sources of commercial controls dried up (world conflict, embargos, etc.) Once proven the U.S. NIST project was eventualy shelved, and EMC2 grew out of its remains as a non-.gov opensource project. Much of the "Big Iron" roots are still around. Existing options include:
    • Seperate home and limt switches.
    • Oil lube alarm inputs.
    • Home to Index
    • Tool tables with both tool# and pocket#
    • etc.... to name a few


    EMC2 REQUIRES feedback. In the case of stepper systems and open loop servos EMC counts its output pulses and computes where the machine would be and feeds this back into itself to make up for the lack of true position input.

  19. #19
    Join Date
    May 2006
    Posts
    2420
    All I was getting at in my original post was that the servo drives mentioned by NJC may accept quadrature instead of step/dir, with the idea that he may be able to use either Mach or EMC without extra hardware, it may be that he has to use EMC if he doesn't want to buy more cards, as mentioned then EMC will take care of the motion control.

    It just sounded funny that a servo drive would take just PWM input and nothing else, wouldn't that just make it a H Bridge ? Where were the encoders plugging in ?

    I for one think EMC is great and I intend to use it as soon as I get time in my life, I seem to be forever building my router and never running it, something I hope to change.

    Russell.

  20. #20
    Join Date
    Feb 2007
    Posts
    592
    Well Russel you pretty much hit it on the head - most amps EMC uses are simple H-Bridges, no encoder inputs to the amps at all.

    As such many of these amps are driven by straight PWM inputs. EMC likes these "dumb" amps as it is better to know where things are in one program than to have serveral "smart amps" running slightly out of sync.

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