Taig, Raspberry Pi 4 & MESA

Hey y'all,

I have a 4 axis Taig mill with the Micro DSLS3000 drive machinery that I've converted to LinuxCNC using a MESA PCI FPGA card and a 7i76 IO card.
Two things have always irked me about this setup:

1. The PC I use to drive it is very unwonderful. It works, but it's another box-on-the-floor-with-wires-out-of-it-for-not-tripping-on, and the fan runs all the time. It's not that loud, but I'd just as soon not have a PC fan running in my workshop.
2. The Microproto DSLS controller reads the encoders on the steppers, so this isn't closed loop to LinuxCNC. I do get per-axis errors if the DSLS feels I'm "too far behind", which is - to me - an unknown number of steps.

I also need to add homing switches to the gitup, so it's due some attention anyways.

It looks like I should be able to replace the PC with a RasPi with a MESA 7c81, reusing the 7i76 card.
For giggles I'd love to close the loop to LinuxCNC, possibly with linear encoders. I figure something like the 7i52 or 7i53 should work to read the encoders, whether I stick with the existing rotary encoders on the steppers or go to linear scales.

Are there obvious problems with this plan that I'm not aware of?

I've been building my own kernel for the damn PC and building LinuxCNC from sources, which is a bit of a nuisance. Are there any distros that give you the PREEMT_RT kernel nowadays? What about LinuxCNC for that config, can I download packages?

Siggi

tommylight wrote:

Moved to "driver boards" section.
There is a ready made official release of Debian Buster with Preempt-RT in the downloads section of the website:
linuxcnc.org/downloads/
Also a ready made image for the RPI4 is there.

Thanks! I hadn't caught onto that.
Also thanks for moving the thread to the right topic. I'm new here .

andypugh wrote:

You could also look at using the 7i92 connected to the Pi ethernet port.

Price is the same, but it does take the ethernet port out of use for networking.

7c81 gives you more IO pins and a pair of onboard smart-serial ports, though, so is probably a better bet.

I like it that the 7c81 also powers the Pi - that way it's fed power through screw terminals rather than a loosey goosey USB-C plug. You also get DIN-rail mounting for the Pi "for free" .

Yes the DIN mount is extra. We should have the plastic DIN trays
for the 7C81, 7C80, 7I94, 7IA0 later this month