Linuxcnc, Gecko G540, and adding more stepper drivers beyond four

[orangezero]

My goal is to get a five axis setup working with my diy cnc, as a learning experience rather than a money-making machine (trying to keep it affordable and reuse what I have if possible).

I currently have an itx intel motherboard with a working built-in parallel port running linuxcnc. My gecko g540 is connected and I'm using all four internal drives.

From my reading, it appears it is *possible* to do some work and get a fifth driver working on a single pci slot. One builder sold them. My other option would be to put a second parallel port in my available pci slot, thus running my gecko g540 with four drivers, and using a breakout board (perhaps like a c10) and one or two drivers (like a tb6600).

Before buying anything else, does this seem workable for linuxcnc? I know a lot of parallel port cards work poorly, so I'll need to be selective. Would a dual pci slot work? Is there an advantage or disadvantage to one? I could always use a newer computer and a dual pci slot.

I perhaps should also add that at this point I don't really run much else besides endstops. No spindle or laser or anything else using any other pins of the port.

Thanks for any guidance.

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[skrubol]

I'd think another parallel port or 2 might work, but you might want to look into the Mesa 5i25/6i25 cards (5 is PCI, $90, 6 is PCI Express, $110.) Not sure how their prices compare to quality parallel port cards that work with LinuxCNC, but they get you quite a bit more flexibility and performance. Not sure how much extra work going from parallel to a Mesa card would be in the config.

[orangezero]

Thanks for the reply. After some more searching on other forums, there are several people who have experience with adding a few extra steppers to a g540 via various ways.

I went ahead and ordered a gecko g251x and hope to connect it to the open pins on my gecko g540 board (as several have suggested) and continue to use it as a "breakout board."

It seems the Mesa cards are a lot more purpose built, but I'm still having a hard time justifying it over a dual parallel port pci card that has been confirmed to work with linuxcnc and is like $13 shipped. I'm not sure I need the extra features provided by the mesa cards, but I'm just using *lowly* stepper drivers, no closed loop, no spindle control, no probes, etc. (at least for now)

[skrubol]

Thanks for the reply. After some more searching on other forums, there are several people who have experience with adding a few extra steppers to a g540 via various ways.

I went ahead and ordered a gecko g251x and hope to connect it to the open pins on my gecko g540 board (as several have suggested) and continue to use it as a "breakout board."

It seems the Mesa cards are a lot more purpose built, but I'm still having a hard time justifying it over a dual parallel port pci card that has been confirmed to work with linuxcnc and is like $13 shipped. I'm not sure I need the extra features provided by the mesa cards, but I'm just using *lowly* stepper drivers, no closed loop, no spindle control, no probes, etc. (at least for now)

Yeah, I guess for $13 it's certainly worth a shot. A second parallel port will give you most of those things you mention even, just not fast and no analog.
I didn't realize the G540 had 2 digital outputs. Good luck with getting it working that way. Will you just leave the g251 enabled all the time or is there a solution to that as well?

[john-100]

from my reply to another thread :-
https://www.cnczone.com/forums/austr...ml#post2212744


It depends on what outputs from the G540 you are using now

the printerport has 12 outputs connected to the G540

8 control the 4 axis (pins 2 to 9)
2 control the open drain outputs normally used to switch relays on and off (pins 1 & 17)
the remaining 2 outputs - pin14 connected to the PWM to 0-10V converter , pin 16 the charge pump

if you don't use the two G540 outputs to control relays ( G540 terminals 5 & 6 )
its possible to use them to control a 5th axis for a rotary table

connect a +5v supply to the + step & + direction to the external driver
the -step to the G540 output1 and -direction to the G540 output 2

the 5V supplies negative terminal to the G540 common (terminal 12)





a modified printer cable could enable the use of pins 14 & 16 for a 6th axis
if you don't want to control the spindle speed or use the charge pump

another way is to add a second printerport or use a motion controller
to use a second G540


John

PS
for your application
you can replace a 2nd G540
with a breakout board and 1 or 2 stepper drivers

[orangezero]

Thanks John. I was going nutty trying to rediscover your graphic earlier today. You basically answered my questions in that other thread.

Since I caught your attention, it seems there is some disagreement over how safe it is to use it this way. My electronics skills are somewhat basic, but the idea behind an optocoupler on a breakout board is to avoid electrical spikes and keep the g540 a bit safer. So, will it affect it? Is it just a matter of time? Or have people successfully used it this way for a while now?

Thanks again!

Worst case, I get a $20 breakout board and a $13 pci parallel port and do it the other way. It seems like doing six axis on one board would leave me with literally no other "things" to add on later.

[PCW_MESA]

If you can run your step motors at adequate speeds from the parallel port with LinuxCNC
and dont need high resolution encoders, there is no huge advantage gained by using a FPGA card like the 5I25.

Because LinuxCNC does all the complex motion control in real time, even parallel port systems can do closed loop,
spindle synchronized motion (threading / rigid tapping) and probing given enough I/O pins. This is one advantage of LinuxCNCs
real time architecture, all motion features are available on any hardware.

Fancier LinuxCNC hardware allows things like higher (and smoother) step rates, high resolution encoder reading,
more I/O expansion, Ethernet connectivity (so slotless MiniPCs can be used as hosts), lower host latency requirements, etc etc

[john-100]

if you connect an extra stepper driver as shown in my diagram in post 5

there should be no risque to the G540
if your adding a stepper driver like Geckodrives G210
or even an ebay THB6064 that have opto-isolated inputs





John

[orangezero]

Thanks again for the replies. I ordered a new pci parallel port card with dual inputs and a cheap generic breakout board. I'll mess around with my new g251x with the breakout board and decide where to go next..

EDIT: Just to be clear, it is my understanding the g251x is not optically isolated, hence my decision to get another board.

[john-100]

the G251 is screw terminal version of the G250 used inside the G540
I can now see why you had concern connecting your 5th driver to the G540

If I remember correctly the G250/G251 is the only stepper driver Geckodrive sell that does not have opto-isolated inputs

the G540's built in breakout board has 17 opt0-isolators to isolate all signals in & out of the printerport
(two HPCL-2531 eight channel isolators and one HPLC-2501)

I have not read of a Gecko driver failing so you can have a large fault current flowing out of the inputs
but using a breakout board on a second port has the advantage of making the two outputs available to control two relays if needed

John

[Rickpt]

I know this thread is a few months old but will this definitely work with the G251X even though it is not opto-isolated? What is the danger of doing this? I also need to add a 5th axis to a G540 based system like many others on this forum without adding a bunch of additional stuff since I already have an investment in the G540 and a UC100. This seems to be a very simple solution if you are not using the two outputs on the g540 however I can't find any posts of anyone doing or trying this. What am I missing?

[OlfCNC]

You can get a higher pin count motion controller for example the UC400ETH, it has 2 ports, one you can connect to the G540 and the other to a BOB and your 5th and 6th stepper drives and other things you might need to connect. The UC400ETH is not much more expensive than the UC100.
I think this is the simplest solution for your problem.

[Rickpt]

I understand how to do it with buying more equipment and rewiring everything like the UC400ETH however I already have the UC100 and G540 hooked up and working well. I was intrigued by the way John described doing it in post #5 which appears very simple. I haven't found a post that anyone had actually tried doing it this way and if this would indeed work with the G251X since that drive isn't opto-isolated.

[Goemon]

Has anyone got Linux CNC working for a 5 axis machine yet (with a g540 plus an extra drive)? I'm interested to hear how it works.


I am currently working on adding a 4th axis and I want to use two motors for my Y axis. I was thinking of adding a second PCI parallel port card and a second G540 but it would be better / cheaper if I could add single additional drives as needed.