LinuxCNC question

[falviani]

Hi,

I have a quick question - it appears that LinuxCNC requires a linux installation with the the real-time options to operate. Is this correct? How much horsepower would be required of the machine? I saw on the website that USB is not considered acceptable as communications. Am I correct in concluding that ALL control functions are carried out by the linux box, and any interface on the router side is simply for motor control signal, electical isolation etc.

I am considering upgrading my current very small machine to something beefier but not a full-on DIY project - an existing kit. So I'd like to know if I should consider any that come up that use LinuxCNC as the controller.

Thanks in advance,
Frank

[herbk]

Hi Frank,

I have a quick question - it appears that LinuxCNC requires a linux installation with the the real-time options to operate. Is this correct?

Yes, that's true. You can download a installable package at LinuxCNC homepage, which is based at a Realtime kernel.
http://www.linuxcnc.org/downloads/

How much horsepower would be required of the machine?

Not very much, i run it at a old HP Laptop with just about 1GHz and 256Mb RAM.
What it makes easy is a parport at the machine. Because the Lapi is broken at July i run it now at a (also old) HP PC with 2GHz and 2Gb Ram, also with a cheap breakeout bord at the parport.
If the PC dont have a parport you have to use a Mesa card, but i don't have any experience with it.

Am I correct in concluding that ALL control functions are carried out by the linux box, and any interface on the router side is simply for motor control signal, electical isolation etc.

Yes, if the PC, where you runs LinuxCNC on, has a parport ( i repeat ) you need only a breakout board and stepper drivers if you have not more as 4 axis.
Something what i like very much at LinuxCNC is the integreated tool to setup the machine. It makes it very easy to test out which speed and acceleration is possible.

[sliptonic]

I have a quick question - it appears that LinuxCNC requires a linux installation with the the real-time options to operate. Is this correct? How much horsepower would be required of the machine?

Your question is probably better answered on the LinuxCNC community but I'll take a shot at it.

There are actually two projects worth looking at LinuxCNC and MachineKit. Machinekit is a fork of LinuxCNC with emphasis on the Hardware Abstraction Layer and provides builds that will work on BeagleBone and other SoC hardware. LinuxCNC is focused on traditional PC builds.

The required horsepower depends on many things including whether you're doing step/direction or servo motors, step resolution, whether you're doing software step generation or using dedicated hardware, etc etc.

I saw on the website that USB is not considered acceptable as communications. Am I correct in concluding that ALL control functions are carried out by the linux box, and any interface on the router side is simply for motor control signal, electical isolation etc.

That's basically correct. USB apparently doesn't have guaranteed timing sufficient for a real-time application. You can't be assured that a required step pulse will happen when it's needed.
On one end of the DIY spectrum you have the RAMPS / GRBL 3D printing world. There's some cool stuff here that is powerful and inexpensive but not industrial grade. The focus is on dribbling the gcode to a dedicated interpreter that turns it into step/direction. The other end of the spectrum is closer to industrial grade. With LinuxCNC/Machinekit, the gcode interpretation and path planning happens on the PC. This is more complicated to set up and more expensive but gives some benefits. You can easily use servos as well as steppers, control up to 9 axes, override the spindle speed and feed rates in real time, pause and restart a running job, etc.

I am considering upgrading my current very small machine to something beefier but not a full-on DIY project - an existing kit. So I'd like to know if I should consider any that come up that use LinuxCNC as the controller.

I've run both LinuxCNC and Machinekit on my machines for years. I've found them both to be excellent projects. LinuxCNC is a viable replacement for even commercial grade equipment. It's extremely configurable and reliable, especially with industrial grade motion control cards like those that Mesa sells.

[falviani]

Thanks for the info! Based on this, I think I'll stick with (most likely) a GRBL-based system. Since this is a hobby and - like everybody else - money is limited, the cost of a LinuxCNC based system seems to be a lot more than I'm interested in investing.

[herbk]

Hi Frank,

... the cost of a LinuxCNC based system seems to be a lot more than I'm interested in investing.

there is not much different if you have an old pc with printerport, - if not you are right...

@sliptonic:
Did you try LinuxCNC at a BB or a RPI ? I'm reading some articles about, but often that it's very slow.

[sliptonic]

@sliptonic:
Did you try LinuxCNC at a BB or a RPI ? I'm reading some articles about, but often that it's very slow.

I used machinekit on a beaglebone black. Using the ui over a ssh tunnel is really slow but usable. Using an hdmi monitor and USB keyboard is very usable.

[herbk]

Using an hdmi monitor and USB keyboard is very usable.

Thx, - do you remember the max jitter you have had and the max possible step frequency?

[sliptonic]

Using an hdmi monitor and USB keyboard is very usable.

Thx, - do you remember the max jitter you have had and the max possible step frequency?

Sorry, I don't. It's been a couple years since I used that particular configuration