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I asked the RPi foundation about this a few years ago, and they said that they were trying to reduce the number of special purpose installations, rather than increase them.
That policy might have changed in the meantime.

16th September 2020:

"Andy

Thank you for your interest in Raspberry Pi.

We're currently not adding many external OSes to the Imager, but please add your suggestion to the github issues and we'll decide what we do about third party OSes. github.com/raspberrypi/rpi-imager/issues

Regards"

Never the less - I believe I have correctly ascertained the math necessary to compute the left and right drum rotation (from home position of 0,0) to achieve a desired X,Y location for the truncation of the two cables. I believe these are inverse kinematics, correct?

correct

I honestly don't really understand what a hal pin is and whether these are required. I'm running my code on a Raspberry pi if it matters.

hal pins are used to connect signals in the hal layer. If your kinematic does do not need real time information from hal (eg tool length) then you do not need to add any pins.

I don't have any feedback in my device so what does LinuxCNC do with the Forward kinematics?

I believe in your case the forward kinematic is only used until the machine is homed. (ie to calculate the initial XY position) But I might be wrong about that.

Note: Looks like it is possible to also run either inverse / forward kinematics only (but I have never used that or seen it used):
linuxcnc.org/docs/devel/html/motion/kine...rward-transformation

My inverse kinematics routine computes the drum rotations FROM HOME to a desired X,Y. Is this correct?

That is correct, for HOME = (0,0) and provided you have not built any offsets into your model (eg a tool-offset)

My CableKins.comp file is attached. I'm basically breaking out of the forward kinematics since that was erroring out but I'm not getting expected results. If you see any glaring issues I'd appreciate any guidance.

So what is the error you are getting?

Hey kind folks,  

LinuxCNC newby here - please be gentle... I'm clearly over my head here... 

I am trying to learn to use LinuxCNC to run a 2-axis cable robot - each joint features a "drum" of known diameter.  The cables from two drums truncate at a single point.  

Eventually I hope to turn this into a low-cost hot-wire foam cutter that would allow you to use G-code to cut out shapes from large sheets of foam. Here is my crude prototype (not working in cartesian coordinates yet). 

photos.app.goo.gl/z3gUimXLRd3yP33W6


I have my mechanism up and running using "trivial" kinematics and if I simply hang a weight from the left drum (mapped to the X axis in trivial kinematics)  and instruct it to move 10mm, the drum will indeed wrap up enough cable to move the weight up 10mm - so I believe I have correctly computed the parameters to account for the various gear reductions, drum diameter, etc.  

So my understanding is that I need to use a custom kinematics file to provide the kinematics / math needed to translate from the desired cartesian coordinates to the resulting joint rotations.  The math is a bit complicated because the cables wrap around the drum and I need to account for both the length of the tangent line as well as the part of the cable wrapped around the drum. 

Never the less - I believe I have correctly ascertained the math necessary to compute the left and right drum rotation (from home position of 0,0) to achieve a desired X,Y location for the truncation of the two cables. I believe these are inverse kinematics, correct? 

Beyond this, I understand LinuxCNC is looking for the "Forward" kinematics -  (given a left and right cable length, what is the resulting X,Y location.  This math is a bit more complicated and required numerical methods (Newton Raphison - basically "guess and check").

I believe I have "solve" both forward and inverse kinematics conceptually - I have verified that my math is basically working - I wrote a simple program using Processing and I can feed in a desired X,Y location and my Processing program will  correctly spit back the change in cable length from home of 0,0.  Likewise, I have confirmed that my Forward kinematics seem to be working - I can input the change in cable lengths (from home) and my processing program will output the resulting X,Y. 

My custom kinematics (attached) will compile but It's not working yet but I have some conceptual blocks that I could use some assistance on that might help me debug.

the man file states:   3) If required, add hal pins following examples in
the template code

I honestly don't really understand what a hal pin is and whether these are required. I'm running my code on a Raspberry pi if it matters.

I don't really understand why LinuxCNC requires Forward kinematics (even though I think I've solved them). I will be feeding this program G-Code with desired cartesian coordinates and relying on LinuxCNC and my kinematics to resolve these to the desired drum rotations (Inverse kinematics, right?). I don't have any feedback in my device so what does LinuxCNC do with the Forward kinematics?

My inverse kinematics routine computes the drum rotations FROM HOME to a desired X,Y. Is this correct?

I'm not sure how all of this works with "homing" With a conventional CNC I understand you would use limit switches to "home" each of the axis but I don't really have that option since there is no physical "home" for either drum (both of which turn multiple turns). My general approach was going to be to manually "drive" the two drums to the known 0,0 and then manually "home" . Is this viable? Any advice?

My CableKins.comp file is attached. I'm basically breaking out of the forward kinematics since that was erroring out but I'm not getting expected results. If you see any glaring issues I'd appreciate any guidance.

Thanks for any nudges in the right direction!

I gave up working with ethercat because my setup needs to be cheap.
It gets expensive when the step driving involved...

I'm going to work with other two options...

Do you have any opinion about raspberry pi's gpio pins? Will I have any problems while working with 5 stepper motors?

Hello, I am an final year Electrical Engineering student of NEDUET Karachi Pakistan. I'm building a 5-axis simultaneous CNC machine as my final year project. When I'm connecting Linux CNC with Mesa 7c81board using raspberry pi 4, there is an error found "No 7c81 board found". Can anyone please help me in this? Well I connected raspberry pi-4 with Mesa 7c81 by IDC40 pin only. Should mesa 7c81 need external power supply for power up? Is this problem occuring due to hardware connection?. 

Hello,
Thank you for this image, it works very well. Unfortunately it is impossible to update my system & therefore impossible to install additional packages, which is a big inconvenience. I just bought a Mesa 7i96s and I need to update my system.

Do you have a solution?

Thanks for your help

2.93 image working just fine with Raspberry Pi 4B 8GB and Mesa 7C80 - right from scratch - great!

Bios power saving options already disabled. It is a dual core processor, isolcpus=1 set, latency max jitter comes 50,000ns to 85,000ns(as the graphics card already removed), ping test data already given in this topic earlier. What else to check? 

One more question: I have a Raspberry pi4, 2GB ram in stock. Any better result expected with that?

A ethercat digital output card can not drive a stepper motor, it is too slow.
Best is to use an ethercat-integrated stepper motor driver, such as rtelligent ect60.
A really slow encoder (a few Hz) can possible be read with the EL1008. The EL510x is otherwise needed, especially for the arc voltage reading.

If you already have stepper motors and drivers, mesa is the best way. There is one card that has all functions needed.

RPI must be near the screen, you can have 30 meter long LAN cable to Mesa and it works even for plasma machines, tested, but HDMI will have huge issues in such environments even at 1.5 meter long cable, and you also need USB for touch screen, probably.

Hello to all.

I'm using LinuxCNC about 10 years with parallel port PC on several machine. They were succesfull setups.

But now I have a new project and I think that something needs to be change...

Let me explain my new project;

• 5 axis, step/dir driven motor drivers
• 1 home switch for each axes, totaly 5
• 1 end switch for all axes, totaly 1
• 1 e-stop
• 4 extra digital outputs
• 2 extra digital inputs
• Sum up;
  • OUTPUTS: 5 step, 5 dir, 4 digital output
  • INPUTS: 9 digital inputs

 

• The LinuxCNC is going to run on Raspberry pi ( not decided whether 4 or 5)
• There is a teach pendant with touch screen( there will be no screen more), everything is going to be controlled by this screen
• The distance between screen and machine will be min. 2 meters.
• The machine is going to be used for welding in industrial environment.

Here is what I couldnt decide or have a reservations...

• If I will place Raspberry pi inside the teach pendant, there will be a 3 meters distance between I/Os and pi. So I have to use MESA board or Ethercat I/O board (I have never used any of them before) to combat with electronical parasits.
  • Negative side of using MESA board is there is no domestic dealers in Turkiye and if I wanted to buy externally there may be some problems with customs. If I overcome this problem, this card is ideal for me...
  • Negative side of using Ethercat I have no information in this world. In Turkiye I can easily find Beckhoff products and I think I have to use EK1100, EL1008 and EL2008 for my setups. But there is a big question for me, Can I drive stepper drivers with EL2008(digital output module) or Do I have to buy a EL7031 (motor controller) ?
    And as a similar question, Can I read an encoder with EL1008 or Do I have to buy EL5101 (encoder reader) ?
• If I will place Raspberry pi outside the teach pendant, there will be a 3 meters distance between the screen and pi. So I will use 3mt HDMI cable. On the I/O side I will use raspberry pi's GPIO pins. Do you think will this be a problem with 5 axis movement?

I know it is a little confusing but its same here ....
Can you offer me an another solution or Is my path correct?

I'm using LinuxCNC 2.9.1 on a Raspberry Pi 400 with Debian 12 "Bookworm" (just for benchmarking, will upgrade to desktop when I get everything installed on a real machine) and connected to a Mesa 7i96s.

The 7i96 is connected to a DM542t, which is then connected to a Nema 23 stepper motor () that is set up for the X axis. I installed everything and ran the Mesa config tool and it shows a connection to the 7i96s.

When I turned everything on I was driving the stepper motor and knew this because it was frozen and I couldn't turn it.

The connection between the 7i96s and the driver is as follows:

Step 0--->Drag-

Step 0+ -> Pool+

Directory-->Directory-

Catalog+ -> Catalog+

I don't know where to start troubleshooting, any information would be helpful.

Thanks.[/url]

I could not use Eagle so I have remodeled Oliver's OCB in KiCad.
I use different connectors. Noved the 5 outputs to the oppesire sides and have 5V/24V selection on all inputs (also wih option to change resisor values). Also added some capacitors.
If I make a new version I would use 6 pin JST to get 5V from the Raspberry PI. Possibly add MAX485+protection circuit to the board.
If there is demand I can put the Kicad files on github.

itai wrote:

I am switching LinuxCNC from an old PC to RaspberryPI + Tango compatible board.
I see that riocore has support for HY_VFD and I want to use it. After resolving simple issues I can get a serial signal out of the Tang Nano, but no connectio to the VFD yet. I guess I will need a TTL to RS485 brekout board. Will this one do?

Last time that I made changes to the HY_VFD configuration it cost me a burnt spindle, so now I'm trying to learn more and if possible from other's experience. I will appreciare any help and suggestions.
Thanks!
-- Itai
 

Is your vesion of the Tango board a modified PCB? and is there Kicad or PCB repository.  Just so I can compare the difference with Olivers version.
Many thanks 

I am switching LinuxCNC from an old PC to RaspberryPI + Tango compatible board.
I see that riocore has support for HY_VFD and I want to use it. After resolving simple issues I can get a serial signal out of the Tang Nano, but no connectio to the VFD yet. I guess I will need a TTL to RS485 brekout board. Will this one do?
Last time that I made changes to the HY_VFD configuration it cost me a burnt spindle, so now I'm trying to learn more and if possible from other's experience. I will appreciare any help and suggestions.
Thanks!
-- Itai