Mesa - Ethernet v's PCI/e

Mesa - Ethernet v's PCI/e for a small mill


Whether to Ethernet or not to Ethernet, that is the question.

I have been trawling through the board looking for commentary on this and have stumbled across a few quotes and comments that provide some insight. I appreciate there is probably no "cut and dry" answer so I will attempt to put a little context down and hopefully those with more experience will be able to shine some light into the dark before I start burning my budget on controller electronics.

A very nice post by #PCW being the anchor to this subject.


What I would like to understand some more is what when the 1Khz of the ethernet should be fine v's when having the PCI model is just safer.

So context. I have a BF20 (G0704) mill that I will convert to CNC. I have 5mm ball screws, NEMA34 stepper motors, proximity senors, Leadshine DMA860H Stepper Drivers etc etc. I have a nice little Dell Optiplex 3020 which has base period max jitter of 8500 after going through some tuning and running an RTAI kernel. I'm a bit if a linux geek so compiling my own software/kernels/custom gui etc is no issue. For example I have played with RT kernels under Mint 18 and latest Ubuntu - including dealing with pulling down all the needed dependencies to get Linuxcnc running.

I have a friend runing Mach3 via a standard PP BoB with the same model machine, very similar spec motors and same PC. He's able to run 800-1000mm/min (31 to 39inch/min) rapids on all axis. He could probably push a little higher but its going faster than his pucker factor is willing to accept.

In my context I have some ambitions that I would like to be able to work towards over time. Some sensible some just "because I can and it interests me".
The basics (stage 1):
- 3 linear axis
- proximity limits on linear axis.
- tool touch off plate (probe if you like)
- eStop

Stage 2:
- 1 rotary axis
- utilise the linear glass scales I have from existing DRO. Maybe moving to PID control of axis or some level of fault control if follow error gets out of hand.
- spindle encoder with A/B and I. I am keen on trying rigid tapping setup.
- motor upgrades with VFD control
- Tormach style tool holding with a pnematic draw bar under software control.

Probably other "bling" that will come to me in time. Yes the mill will be as much a hobby project as it will be a peice of working equipment.

PC location: I have built a custom stand for the mill which has plenty of room under it. It is very easy to house the CNC electronics case and the PC all in the mill stand with room to spare for tools and drawers.

Looking at the MESA site there seem to be lots of choices but based on what I have seen others doing/talking about and the number of Inputs and outputs that would be likely needed the choices would seem to be:

PCI/e:
5i25/6i25 --> 7i76 (easily sourced from a local supplier makershop.co.nz)
Given my PC has PCIe lets assume I could go with the 6i25 based combo.

Ethernet:
7i76e (will have to be sourced from USA and imported, not the end of world just no local support if something goes bung)
7i96 (does not look to have sufficient connectivity. I also like the VFD 0-10v control available on the 7i76 classe cards. Would seem to be a good choice for perhaps for a plasma table build in the future)

Both setups look to have the same connectivity based on reading the manuals.
I dont't need ethernet for remote/convient locaiton of the PC (see PC Location above). But I acknowledge the ethernet solution would be very contained and "clean".

From a performance angle given what pace (800-1000mm/min rapids) I am looking to achieve from the mill is there a h/w choice that stands out for some reason?

Have I missed a key consideration?

Appreciate any adivce folk are able to provide and perhaps expand on the merits/gotcha's of the ethernet v's PCI/e choice.

Thanks,
James.

As I mentioned before, on step/dir systems there really is no reason to need a faster than 1 KHz servo thread, so the interface you use should be chosen for other reasons. Its a bit more trouble to get a Ethernet system going because network setup is involved and you need a Preempt-RT kernel but if you are familiar with Linux that should not be an issue.

@PCW - thanks. I guess cross checking against the likes of RodW who has based a big plasma table off the 7i76e. His rapids and cut speeds are far in excess of anything I will be using on the mill. Based on that the Ethernet link will be fine.

As you say comes down to availability, local support, lack of interest in doing more software and networking gymnastics.

I am interested in the 5v isolation point that was made. Is the common ground comment for the pci link much of a concern? I had though things were all opto isolated from the “parallel” port connection between 6i25 and 7i76? Unless you jumpered to utilize the 5v from the 6i25?

Sorry - electronics is not my strong suite.

Cheers,
J.

Its a bit more trouble to get a Ethernet system going because network setup is involved and you need a Preempt-RT kernel

Why the PCI doesn't require a Preempt-RT kernel?

My understanding is that the PCI/e cards can use either RTAI or Preempt-RT kernels. Where as the Ethernet based cards require the Preempt-RT as the linuxcnc ethernet driver loads into user-space.

Cheers,
J.

Joco. I forget now are you in NZ or AU? There is a Mesa dealer in NZ.

Really, the support PCW gives on this forum is way better than what you would get from a local. To build new firmware for me overnight after I blew up an encoder input on my 7i76e is just amazing. Anyone else would have sold me a replacement board.

I went with the 7i76e because I was building a plasma machine which is known to be a noisy environment so I could get the PC out of harms way.

For a milling machine, I would consider a PCI/e solution and use a 12 volt motherboard and wire it in as if it is was just another control box component. This is the approach Andy takes. So I think the choice depends on your overall machine design.

One minor annoyance with the ethernet one is that your control box needs to be turned on before you start Linuxcnc. With the PC in the control box approach this won't ever be an issue.

Hi Rod. NZ mate. Yeah Makershop is local. They only stock the pci/e stuff though.

Support wise, agree. Forum support is going to be critical with the likes of PCW clearing the fog. I started snooping at the config wizard for mesa cards, yikes! Way more options and sub tabs ro get lost in compared to the parallel port version.

I already have the controller box which is a re purposed rack server case. Its not large enough to hold a pc MB, video card, ssd as well as everything else. So i am going with seperate PC and CNC boxes. Treating those as a two building blocks linked with a cable will work ok.

You do raise a good question, can anyone tell me if the pci/e board will care about the order PC vs CNC enclosure is powered on?

Cheers,
J.

The card FPGA will not care but if you use either a 7I76 or a 7I76E, the system (FPGA card _and_ 7I76 or I/O section of 7I76E) must be powered before LinucCNC can start.

Its possible to detect if the I/O hardware has power so you could make a script that just waited for the hardware to be powered up before launching LinuxCNC, perhaps with a "Waiting for system power" message.

Thanks PCW.

Assuming I am going with a 6i25+7i76 combo, my understanding from your explanation is that the PC in of itself does not care if its powered on before or after the CNC electronics are.

What matters is that when loading a config into Linuxcnc with HAL components/drivers that expect the Mesa h/w to be present that the 6i25+7i76 are powered.

Which means I can load sim configs and run simulations of gcode files to ensure it looks ok. Then power up the cnc h/w block (which would include the 7i76), restart linuxcnc with the Mesa config and would be good to home axis, setup the work piece etc etc.

If I have this all turned around just kick me and tell me what I have mucked up.

Cheers,
J.

I thought it might be useful to find and show some examples of just how fast the movement an ethernet connected board like the 7i76e can achieve. Nothing like actually seeing stuff to understand how fast is FAST.

Utilising some great footage from RodW's build:

General large scale movements.


Cutting some parts so slow cutting movements and fast rapids on repositions.


While this is plasma and not a Mill the point is to show that the 1KHz "speed" on the ethernet connections can run steppers at a pretty fast pace.

Cheers,
J.