Connecting to a pen plotter

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09 Jul 2019 14:52 #138955 by lynsg
Hallo, I wonder if I could ask a couple of questions here please.

I find myself needing to build a pen plotter, around 2m on the rail and 1m on the gantry. As I have zero history with CNC kit of any sort I have started by installing LinuxCNC 2.8 on Mint 18.3. The machine is a Thinkpad T520, with latency while doing nothing else of 20,000/27,000 or so. It will be doing nothing else while running the plotter.

As far as I can see from reading up, I need to build the plotter with an Arduino, a shield with drivers and PSU, and connect the Arduino to this machine with an ethernet cable. Is this broadly correct? While I need to pick some firmware to load onto the Arduino, the current installation of LinuxCNC is sufficient? Does the Arduino firmware need any particular characteristics to match LinuxCNC?

Thanks
Lyn

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09 Jul 2019 15:07 #138957 by DinukaShehan
I don't think so!

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11 Jul 2019 10:13 #139094 by lynsg
Replied by lynsg on topic Connecting to a pen plotter
Now that my installation has survived several reboots without self-destructing again I have started going through the documentation and find that LxCNC works quite differently to others that I've been reading about.

So, I need a parallel-port board like this: www.omc-stepperonline.com/cnc-breakout-b...outer-kit-st-v2.html which they say works with LxCNC, hooked up to the stepper drivers.

I also need a little servo to lift the pen. Robot shops etc have small servos that are only a fraction of the weight of a small stepper with a lead screw, but it's not clear how best to drive one.

Searching this forum for 'servo' produces nothing of relevance - can LxCNC handle a little servo of this type? If I've missed the relevant documentation would someone please point me to it.

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11 Jul 2019 10:22 #139097 by tommylight
You can use Linuxcnc without a break out board, you just have to be careful when wiring things.
The cheap ones cause more trouble than they are worth.
Using RC servos is not adviseable as they require precise timing for controll from 1 to 2 ms.
For a pen you would be much better off with an electromagnet pulling it down, you can make one easily by winding a lot of isolated wire or you can find a lot of them on old photocopiers.
Also using a small DC motor with a cheap drive or a single darlington transistror and a resistor will do the job nicelly and you can controll the pressure from Linuxcnc by PWM.

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11 Jul 2019 16:34 #139116 by lynsg
Replied by lynsg on topic Connecting to a pen plotter
Thanks for that. I found a mini stepper with lead screw and 38mm travel on ebay so bought it.

The other thing is that, because this T520 laptop doesn't have a parallel port, I was thinking of plugging an adaptor into either the expressCard slot or the serial port, or even a usb port. I suspect there may be pins missing in the output though. (I know laptops are frowned upon, but this is only to run a pen plotter for a few minutes now and then. And accuracy only needs to be within 1mm).

It would make sense to use ethernet if possible, but I still haven't found a starting point on the forum or the docs to clarify how to do this. Has it been documented somewhere?

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11 Jul 2019 21:08 #139126 by tommylight
You can use a Mesa 7i92 or 7i96 or 7i76E, all are ethernet cards that work perfectly with Linuxcnc.
USB and serial can not be used to controll a machine, due to latency and lag issues.
That Lenovo might also prove unusable for machine controll due to latency as it has a lot of power saving stuff implemented, good for battery life bad for machine controll.
I had several T420S and other Lenovo, still have a T420S, it is unusable as it will drop the connection to the Mesa 7i92 at random, so i use it only for testing, not for running a machine.

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12 Jul 2019 06:02 #139145 by lynsg
Replied by lynsg on topic Connecting to a pen plotter
Thanks for laying that out.

I think the best way forward for this current project with the pen plotter will be to use the java Universal Gcode Sender along with a usb cable.

The next project will be for a far more substantial machine, for which I will come back to LxCNC and choose dedicated hardware to suit the job in hand.

In the meantime I will contribute any gcode conversion scripts I write once they have been properly proved in use.

Cheers.

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12 Jul 2019 07:16 #139152 by pl7i92
Replied by pl7i92 on topic Connecting to a pen plotter
i woudt like to ask you
what is the main use of it
drawing things
cutting mask
engraving
the rig you setup is mainly universal corrdinate
but as i see no z only in out

you can with the arduino LOW precision do all
there is Estlcam on the market
it offers a all out board 35USD
woudt be worth to get a view

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