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

Hey Guys,

i would like to set up my first cnc machine with Linux CNC and Clearpath servos... what are my best options for a controller board...

i dont have anything invested in the pc yet so i would love options on usb vs parallel interfaces as well..


thanks

Joe

Your options with LinuxCNC are parallel or Ethernet. LinuxCNC is a software real-time motion controller that interfaces to the hardware using a breakout board (BOB) connected to the parallel port. Or, if you use a Mesa card (Mesa Electronics) you can get one that has an Ethernet interface. They are really nice cards and provide plenty of I/O of various types. Controller boards are just that, motion control implemented in the hardware. These are the ones that will often have a USB interface and cannot be used with LinuxCNC.

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Originally Posted by rcheli

Your options with LinuxCNC are parallel or Ethernet. LinuxCNC is a software real-time motion controller that interfaces to the hardware using a breakout board (BOB) connected to the parallel port. Or, if you use a Mesa card (Mesa Electronics) you can get one that has an Ethernet interface. They are really nice cards and provide plenty of I/O of various types. Controller boards are just that, motion control implemented in the hardware. These are the ones that will often have a USB interface and cannot be used with LinuxCNC.

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thank you .. im picking through it now...

There are several other options with LinuxCNC.
As well as ethernet cards, Mesa have PCI and PCIe card with an external board. However once installed there is little difference between say a 5i25 and 7i76 (or 6i25 and 7i76) or the more recent ethenet 7i76e I use (which requires a different Linux Kernel).
Pico Systems have some solutions for some servos.
Ethercat and General Mechatronics offer solutions.


All I would say is ask on the LInuxCNC forum and don't select clearpath servos for the sake of it, there could be better servo based options that work with LInuxCNC.

LinuxCNC will never support USB as its not real time

"LinuxCNC will never support USB as its not real time"

One wise man once said never say never. :)

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Originally Posted by OlfCNC

"LinuxCNC will never support USB as its not real time"

One wise man once said never say never. :)

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A pretty safe bet in this instance. USB is a serial device and therefore suffers from latency so its not possible to guarantee within the strict timing parameters of the linuxcnc servo thread (usually 1 ms but sometimes faster).
This is the fundamental difference between the Linuxcnc paradigm and windows based systems. Because Linux offers a real time operating system LinuxCNC IS THE MOTION CONTROLLER. In a Windows environment, the OS is not real time, the motion controller is moved onto an external board (Smoothstepper etc). Thats why these devices are also never going to be compatible with Linuxcnc as a CNC machine does not need two motion controllers!

So in the case of a Mesa card, Linuxcnc tells it to generate a step frequency for each step generator and the Mesa card happily outputs that frequency continuously until told otherwise (which LinuxCNC can do 1000 times a second on the servo thread). By offloading the step generation to external hardware, the requirement for software step generation used for parallel port breakout boards on a separate and faster base thread is removed and the latency requirements of the PC are substantially relaxed. In fact, on a Mesa system, the base thread is not invoked.

Because Linuxcnc IS THE MOTION CONTROLLER and it you can write your own components in C which are then part of the ecosystem. These components have direct access to the motion controller itself, it is an extremely flexible environment. Whilst a simple milling machine would be pretty easy to knock together, much more complex devices can be built and controlled. For example, plasma torch height control can monitor torch voltage and control torch height (by taking over Z axis motion) without the need for external hardware used in a Windows environment. Or a builder who did not quite get his machine 100% square on the X&Y axis can automatically compensate for his blunder without the motion controller ever knowing!

OK but it does not need 2 motion controllers does not mean that it can't have 2.
I think less people using closed loop systems (servos) than how many using open loop drives (steppers) and probably it could work in an open loop system, because there the latency is not an issue.

I don't really beleive in realtime operating systems. It's fine that it is realtime, but who guarantees that it will be not overloaded by the user? Users are often geniuses. :)
I like the external realtime microcontroller or FPGA as the motion controller solution, I feel it more reliable but maybe it's just me.

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Originally Posted by OlfCNC

OK but it does not need 2 motion controllers does not mean that it can't have 2.
I think less people using closed loop systems (servos) than how many using open loop drives (steppers) and probably it could work in an open loop system, because there the latency is not an issue.

I don't really beleive in realtime operating systems. It's fine that it is realtime, but who guarantees that it will be not overloaded by the user? Users are often geniuses. :)
I like the external realtime microcontroller or FPGA as the motion controller solution, I feel it more reliable but maybe it's just me.

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CNC is all about coordinated motion of axes to follow a toolpath. there can only be one boss of this process.

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.

The power of a full blown PC just leaves the FGPA for dead in terms of CPU processing capability.... Compare the ESS step gen of about 2-3 mHz vs Mesa's FGPA at 10 mHz..... maybe its trying to do too much....
I think coming from Windows, the concept of a Real Time OS is a bit foreign to you... Why did Tormach and CandCNC move away from Mach3 to using LinuxCNC and Mesa FGPA hardware?

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.

Hi,
For Growing your Business you need attractive design. My personal experience with https://mycncstore.com/ this site is very good and the owner of this is very knowledgeable person.

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.

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I don't really beleive in realtime operating systems. It's fine that it is realtime, but who guarantees that it will be not overloaded by the user

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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.

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Why did Tormach and CandCNC move away from Mach3 to using LinuxCNC and Mesa FGPA hardware?

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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.

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Originally Posted by cyclestart

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.

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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

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Originally Posted by ger21

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.

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I dont think so, AFAICT, the ability to fix bugs and add deep features (not just window dressing) themselves was a major factor.

That's kinda what I said.

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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.

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How could an axis lag behind? They are controlled with one realtime FPGA.

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Compare the ESS step gen of about 2-3 mHz vs Mesa's FGPA at 10 mHz..... maybe its trying to do too much...

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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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Originally Posted by 109jb

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.

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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.

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Originally Posted by cyclestart

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.

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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!

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.

https://www.youtube.com/watch?v=WZ60jBCT94w