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Rather than starting a new thread about jitter mitigation, I'm just going to add it here.

First, I'm keeping in mind that Peter Wallace said " The jitter is basically unimportant with a 7C81 unless its so bad you
get real time errors at the normal servo thread rate ."

I'm also treating the Raspberry Pi + 7C81 as a dedicated controller, not a PC. By that I mean I'm not going to be doing anything on the Pi except LinuxCNC. I may turn on WIFI to update packages, or use email to transfer a file. But I plan to even turn off WIFI before I launch LinuxCNC.


I ran several tests to see which combination of settings offered the most optimized jitter. I ran two Glxgears for all tests as I though that was reasonable, and ran the tests for long periods of time unless they looked bad early on.

I thought that turning off all unused services would decrease Jitter. So I turned off 9 of the 23 services, such as CUPS, Bluetooth, etc. To my surprise this did not decrease jitter.

Screen blank increased jitter a bit, so I turned that off. It doesn't make much sense anyway on a CNC controller.


These are the settings I added to the line already in /boot/firmware/cmdline.txt:
I tried a few others that some people recommended on various blogs. Nothing else I tried had any noticeable positive impact on jitter, and some noticeably slowed down the responsiveness of the Pi.


Turning off timer_migration did reduce jitter. What I read said that you could make this setting permanent by adding it to the boot command line, or setting it in either of two different system files. Oddly none of that worked. So I setup a cron job to disable it at boot, and that works.Add the following line:

The other thing that helped reduce jitter was changing the scheduling policy to real-time and increasing the priority. I decided to create a shell script to launch latency-histogram, and eventually linuxcnc, which changes these things on the process.
I named it rrt (run real-time). So to launch latency-histogram it's simply:
All spawned sub-processes inherit the policy and priority. So if linuxcnc is launched with rrt:all of the processes that are part of LinuxCNC have the policy of SCHED_RR and priority of 99. I used Round Robin scheduling to make sure no LinuxCNC process "starves" another.

I don't know if this will work in the end, but I'm going to give it a try. Nothing ventured, nothing gained.

Implementing all of these, here is the jitter histogram. Good enough.

 

hello hmnijp,
could you please elaborate on that? 
I have tryed to comment out this section of the code in interp_arc.cc and then make the build, but I still get error message.

Hi Automata,

I can use the servo's if they are powered 230volts. Then they can be used to finish and test ethercat auto installer. And runtime tests.
My mail : This email address is being protected from spambots. You need JavaScript enabled to view it.

For the planner. If you program a square 100x100mm and use G64 P5
It should show blended corners at runtime.
Works also for G3 to G3.

Thank you for sharing findings.
I am trying to achieve the same for Delta B3 drives.
i have questions regarding two points:

1. cia402.comp line 240
      change (statusword >> 10) to (statusword >> 12)
-  did you download this component from github.com/dbraun1981/hal-cia402/ and manually compiled and installed it?

4. cia402.ini
       in [joint_0] be sure:
           HOME_SEQUENCE = 0 (or whatever sequence number is appropriate)
           HOME_USE_INDEX = YES
           HOME_SEARCH_VEL = 0
           HOME_SEARCH_VEL = 1 (or any non-zero value)
- here is HOME_SEARCH_VEL stated two times - maybe one should be HOME_LATCH_VEL?

 

Computers do not care much about temperature on the low side, the used "Enterprise" ones i use are perfectly fine even at -5 C, yesterday all day long, not a single issue.
So if yours is having issues at 0, there is something failing inside, probably power supply as noted by beeps, and it will sooner or later fail even in hot environment.
I have several of those in shops with no heat around here, not just one, i am sure some worked even at -8C.
I am also sure some will fail to start at +5C, and always that is a sign of something failing, and as with everything some will work for many years and some will not.
Computers do care about moisture, and i have several dead from it every year.
TL:DR
CPU's do not care up to -70 or even much more
Capacitors do care a lot
Resistors do care a bit
etc...

Hello all,

I have fun with my converted milling machine and we are preparing to move it to its final place in the shop but now the computer is starting to act up.
The machine is standing in a workshop that is not heated or insulated. So the Computer (hp ProDesk Mini PC) is exposed to really low temperatures. Up until the start of this year it was never an issue but now the computer crashes shortly after booting and starting LCNC. I know this has to do with the cold because I moved the computer inside and after it warmed up I was able to run it just fine. After moving back to the shop it gave me about 20 minutes of work before crashing again. (Likely after cooling down enough) At some point while trying to boot and crashing the computer was beeping in a way that indicated a power supply issue.

The computer was exposed to 0°C (HP datasheet rates it to +10°C). I know the Mesa cards are allowed to handle 0°C but the computer seems to have taken some damage.

It was only a 100€ computer and I was able to save my configs so I'm not to sad if it has taken permament damage.

I have now bought a heating cable used with water pipes which gently heats the computer up with 64W of heating power and a thermostat but after a first test it only ran for 5 minutes.

TL;DR:
I have a computer that was affected by freezing temperatures (0°C)
now it won't run for long
I need a good solution (heating the shop unfortunately not an option)
Does anyone know Computers that handle the cold?
Any other experience?

Before that I had already assembled CNC machines and 3D printers. But it was much easier with them. There was a board already prepared for a milling machine or 3D printer. I edited the Marlin firmware file and uploaded it. That is, I had work with CNC. I have never dealt with FPGAs. Installing LinuxCNC on real hardware is not a problem. Buying a ColorLight board is also not a problem. I have been working with a soldering iron all my life))) But I have never worked with Linux))) That's why it's a dark forest for me. I read on GitHub how to flash a board and make inputs/outputs by cutting tracks and a resistor, I don't remember exactly))) First, as I understand it, you need real hardware, the ColorLight board itself - flashed. And then its configuration. But I didn't find any information about setting up the board.

Could mapping of the rack be possible as some do for ballscrews\leadscrews ?

Unfortunately I’m not really up on the implementation.

I wouldn’t be of the opinion USB = bad. I think it can be let down at the physical layer by less than great cables.
Whilst not the greatest fan of Arduino, it does allow for projects like yours and sharing is quite easy. Developers such as yourself should be thanked, as there is a lot of behind the scenes frustrations, hopefully you didn’t pull too much hair out. Keep up the great work.

Just another thought, Ethernet would add a bit of extra cost, and could mean a 2nd Ethernet card for the pc and such. And complexity for some setting it up. USB\Serial keeps it easy.

All the best from Down Under
Rob