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Thread: Setting up Linux CNC with Clearpath Servos. Best controller board to interface with?

  1. #13
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    Default Re: Setting up Linux CNC with Clearpath Servos. Best controller board to interface w

    Quote Originally Posted by cyclestart View Post
    My only experience outside Linuxcnc is the big dollar industrial controls from many years ago so I won't try to compare to everything else available.
    My machines are all open loop and the motherboards are old Atoms that really should be replaced except for laziness and the 'don't mess with a running piece' mindset.
    Step pulses are software.

    That situation has happened. Whether due to something running in the background or the low spec of the hardware, the computer could no longer responded to mouse and keyboard, what people sometimes call freeze or lock-up. The machine didn't lose a beat and the part was good.

    I first learned what exists inside/outside realtime the hard way. With a large program loaded keyboard jogging did something unexpected due to response lag.
    Now finally to the question. Does using external hardware (Mesa or other) reduce that response lag ? Question asked in relation to possibly adding an MPG to one machine.

    btw: 109 That last sentence ? We know what you meant.
    Yes, you can get very low latency from LinuxCNC buttons/MPGs if they are connected to realtime hardware: (parallel port, RPI GPIO,Mesa, PicoSystems, General Mechatronics, Ethercat etc)

    Typically these will be read/acted on in the servo thread so less the 1 ms latency

    Last edited by PCW_MESA; 01-10-2019 at 03:59 PM.


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    Default Re: Setting up Linux CNC with Clearpath Servos. Best controller board to interface w

    Quote Originally Posted by ger21 View Post
    Mach3 has a lot of bugs, and features that don't work properly, and it was no longer being supported.

    If it was bug free, and fully functional, they likely would have preferred a Windows control to a Linux control. As most people would.
    I dont think so, AFAICT, the ability to fix bugs and add deep features (not just window dressing) themselves was a major factor.



  3. #15
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    Default Re: Setting up Linux CNC with Clearpath Servos. Best controller board to interface w

    That's kinda what I said.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Setting up Linux CNC with Clearpath Servos. Best controller board to interface w

    Latency remains an issue with stepper motors as the trajectory planner is all about coordinated moves, toolpath, path velocity etc. Imagine if an axis lagged behind
    LinuxCNC will report if the latency exceeds allowable limits. eg. the Servo thread can't service everything in time.
    How could an axis lag behind? They are controlled with one realtime FPGA.



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    Default Re: Setting up Linux CNC with Clearpath Servos. Best controller board to interface w

    Compare the ESS step gen of about 2-3 mHz vs Mesa's FGPA at 10 mHz..... maybe its trying to do too much...
    Yes that's too much 4MHz is already too much. it is noise sensitive to send that short step pulses where there is no error correction at all. There is etherCAT and CAN buses and analog +-10V for that high frequencies.



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    Default Re: Setting up Linux CNC with Clearpath Servos. Best controller board to interface w

    Quote Originally Posted by 109jb View Post
    Latency is more of a problem with open loop steppers than it is with a closed loop system. Any hiccup in the step pulses can be thought of as an acceleration or deceleration of the stepper. A big enough hiccup and it acts like an instantaneous acceleration that the motor can keep up with and it stalls. Depending on the closed loop system you have, it can make up for the above. A closed loop cannot.
    Thats not really applicable for LinuxCNC. Latency in a LCNC context is a function of the hardware. Sometimes you can fix it with BIOS settings but if its not good enough, you need to change your PC.

    Quote Originally Posted by cyclestart View Post
    Now finally to the question. Does using external hardware (Mesa or other) reduce that response lag ? Question asked in relation to possibly adding an MPG to one machine.
    Some Mesa cards (like my 7i76e which has 2 of them) have MPG inputs built in. I've found they work well. Mesa also make a daughter card specifically for consoles and pendants (the 7i73) so it would be possible to build a hardware pendant or console that would give full control of your machine without needing to touch the keyboard. In my case, I use a 433 Mhz wireless pendant that has a relay box/receiver inside the control box that is hardwired to the pendant buttons because when you have 32 inputs and 16 outputs you can do things like that!

    Rod Webster
    www.vehiclemods.net.au


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    Default Re: Setting up Linux CNC with Clearpath Servos. Best controller board to interface w

    I have stress tested a ton of linuxcnc real time systems. As rod has said- the computer hardware needs to play well with real-time kernel. If it does (which in my experience is more likely than not) it 'just works' tm. I have pushed systems to swap without it missing a beat.

    Here is a laptop running a win 10 vritual machine while running a mill. It really is amazing.





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Setting up Linux CNC  with Clearpath Servos. Best controller board to interface with?

Setting up Linux CNC  with Clearpath Servos. Best controller board to interface with?