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Good day all,

I wanted to share my experiences using the Raspberry Pi 5 to run my CNC machine and ask for some advice, as I am not sure where to go from here.

Please note, I am a novice at best!

To my surprise, I managed to set up LinuxCNC with EtherCAT to run my A6 servo motors that I got from StepperOnline. I am using the Probe Basic UI, and I love the setup so far. Big thanks to RodW for all the work and instructions on setting up EtherCAT.

I am also using an Arduino Mega connected to the Pi for general-purpose I/O—this also works great. (Using LinuxCNC_ArduinoConnector from: github.com/AlexmagToast/LinuxCNC_ArduinoConnector) This will mainly be used for buttons and tool changer I/O, so latency is not an issue. An EtherCAT I/O module would be better, but they are rather pricey.

What I would like to do is add a step/dir interface for my Z-axis, as this is still driven by a closed-loop stepper motor (my X and Y axes are EtherCAT). I want to be able to run the motor at a maximum of 200 kHz step rates. In the future, I would like to add a second Z-axis as well.

What I have tried:

• Using the GPIO pins from the Pi, but this does not generate step rates fast enough to run the motor. This also causes some latency issues, as the step generation is now done on the Pi.
• I switched out the Pi 5 for a Pi 4 (since SPI is not supported on the Pi 5) and tried using the Remora SPI interface to run a BTT SKR 1.4 as an external step generator. However, this also had a maximum step frequency that was too low. Additionally, I would prefer to use the Pi 5 instead of the Pi 4.

I would also like to build a second machine using only stepper motors with a step/dir interface. My motor drivers accept a maximum of 200 kHz.

I am looking for a solution that will allow me to run LinuxCNC on a Pi 5 with external step generation around 200 kHz that is not too pricey.

Any advice on which direction I should go next would be greatly appreciated.

Thanks for clearing that up Rod, it made sense in my mind, which was probably a bad sign.

As a band aid solution I extracted the files from the ethercat-dkms package and ran the update script in the directory for the boardcom stuff, which is a pain as the whole linux sources are need, not just the headers. Anyways some of the patches failed so I gave up on the theory.

unknown wrote:

As of Feb 4th 2025 the the 6.12.xx series kernel is not supported by Ethercat, so installation will fail. 

Only installation of Ethercat will fail. I have raised an issue with etherlabmaster on their gitlab repo asking if they have a time line for 6.12 support.
I alos pointed out they should get their finger out as Debian Trixie is only a few months away and it is currently running 6.12

As of Feb 4th 2025 the the 6.12.xx series kernel is not supported by Ethercat, so installation will fail. Those wanting Ethercat are encouraged to use the previous version. This is one of the pitfalls of creating images, if a older kernel is used people get upset, if a newer kernel is used people get upset. Eevn if we had of used the Rpi kernel that is "current", 6.6.x series, Ethercat would have the same issue.

Rodw is on to it and has raised the issue on the github repo.

www.linuxcnc.org/iso/rpi-4-debian-bookwo...23-11-17-1731.img.xz
www.linuxcnc.org/iso/rpi-5-debian-bookwo...23-11-17-1520.img.xz

"Does not work" is useless without further information. We do not read minds, I at least don't like playing 1000 questions.

If you have issues writing the image to an SD card, try extracting the image from the downloaded file (don't ask me I don't use windows), as the file is compressed to save space and time downloading, then try writing the image. If that fails check the sha256 sum. Tho if the file is corrupt extracting file will likely fail anyway. So check it first.
www.linuxcnc.org/iso/

There is a small patch to allwow the kernel to make a sysfs entry that Linuxcnc and some other programs use to determine if the kernel is a realtime kernel.

forum.linuxcnc.org/media/kunena/attachme...ernel-realtime.patch

forum.linuxcnc.org/38-general-linuxcnc-q...6-12?start=10#315437

@ elovalvo Thanks for your work on this. I am trying to stay within RPI OS and compiling my own kernel. Can you tell me why I still have to patch the kernel, even though RT_PREEMPT is supposed to be a part of the mainstream kernel now? I am using the latest 6.6.74.

>Len

Desiccant sounds good at first, but these do "fill up" quickly. I have dozens of these bags in a 3D printer filament storage container. Even though it is completely sealed (with a gasket), all those bags are only good for about a year. Then they all must be baked at 110degC for 8-12h to rejuvenate them; moisture is insidious.

If you try this, place a quality hygrometer inside. Will likely find that the humidity stays low for only a month or so, even with a good seal.

The moisture alone probably is not causing the inability to start. The way most computers and power supplies are designed, just is not favorable to low temperatures. Very few are, because that is not a typical use case for a computer. Section 5.6 of the RaspberryPi4B says that is good down to 0degC - but then must consider whatever power supply is used for it. The characteristics of semiconducting materials changes as temperature changes, so functionality at low temps has to be something designed into it. Once had a quirky home computer that "complained" at 19degC and refused to run at 18.

If it were my machine, I'd put a heater (like a hair dryer on low setting) near the computer, along with a thermostat. Set the thermostat to say 20degC, and just let it warm up until the thermostat starts cycling. Of course need to be careful nothing can get too hot. Warming should take an hour or more - rushing it is not advised; the whole computer needs to warm up slowly. Then run the machine. That may be easier than re-engineering a quirky power supply or replacing the computer.  Unless anyone knows of an industrial-rated computer (and power supply.)