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16 Mar 2019 08:28 #128715 by JTknives
New to all of this was created by JTknives
So first off I would like to thank anyone who can point me in the right direction.

I have been building a plasma cutter for my shop and I am having doubts about my original choice for a controller. In ordering all my components I had a knee jerk reaction and bought the masso controller. I will start by saying it is an easy to use controller but the more I play with it the more I become concerned that it’s not really ready for prime time. Also I noiticed it tops out at 100khz which seams kinda low. What first got me rethinking this build with the masso controller was wanting to incorporate a THC. Also people seem to keep having issues with weird bugs cropping up. That would not be a problem if it was open source but it’s not. I can still return the controller so I’m looking at LinuxCNC. I figure for the $600 I paid for the masso I could get set up with a nice system from masa.

So I come to you with open arms pleading for some guidance. I have a hypertherm 30XP but it’s being upgraded to a 45xp next year. I built a floating head into the Z with a switch as a back up for ohmic. So with that said is this even feasible to undertake considering I have zero Linux experance. I have dabbled in computer programming in my younger days. I am a machinest by trade and no stranger to cnc and hand wrighting gcode.

I popped over to the masa website and quickly realized I was in over my head as the board numbers ment nothing to me and I did not know what I really needed from them. So like I said here I am looking for some guidance.
Thanks guys - Jarod
JT Custom Knives

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16 Mar 2019 11:39 #128721 by andypugh
Replied by andypugh on topic New to all of this
100kHz at 8x microstepping is 3750rpm, It is very hard to get a stepper to spin that fast, so I wouldn't necessarily worry about the pulse rate.

You will feel a lot more in control with LinuxCNC. But I have never used it for Plasma, nor have I used the Masso, so can't say whether LinuxCNC will actually be better.

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16 Mar 2019 12:36 #128727 by rodw
Replied by rodw on topic New to all of this
Don't worry about your lack of Linux experience. You are driving a CNC machine not a web server so you will be fine from the menus.

If you download one of the LinuxCNC ISO's it will install the Linux OS and install Linuxcnc all at the same time.

If you have a gantry machine, you are probably better off installing the development branch (We call it master). There is an ISO for it here:
www.linuxcnc.org/testing-stretch-rtpreempt/
Assuming you have a 64 bit machine in this day and age, this is the file you probably want. linuxcnc-stretch-uspace-amd64.iso
This is becasue it has better homing features to square the gantry when homing. You can then just square the gantry by changing an offset in your config.

Linuxcnc has 2 main types of text based configuration files. The ini file that describes the main machine parameters, which gui to use, axis lengths, stepper scaling etc and the hal file that loads the hardware and wires the physical inputs and outputs (pins) to internal pins that make Linuxcnc do something. There are GUI based configurators for parallel port breakout boards (stepconf) and mesa cards (pncconcf). Really these are designed to get your machine using and then you need to rollup your sleeves and edit the config files by hand (particularly for plasma)

As far as Mesa hardware goes, Assuming you have a stepper driven machine most people use an ethernet card version for plasma so you can move the PC away from the machine for noise. There are two you could use. The 7i96 which has fewer inputs and cheaper but the 7i76e can drive 5 steppers and a lot more inputs and outputs. From my experience plasma seems to want a lot of I/O so the 7i76e is a better option in my view.

So to read the arc voltage Mesa have a THCAD board which comes in 2 versions. One set up for 300 volts for raw arc voltage input and another with a 10 volt scale for use with divided volts (and which can be scaled to any voltage scale by adding resistors. The THCAD converts the voltage to a frequency which is connected to the spindle encoder input and we do some maths in the Hal file to convert the frequency to volts. In your case, I don't think you have a voltage divider yet I would suggest you go with the THCAD-10 and mount it on a Jiffy box or something at the plasma cutter with a scaling resistor on raw voltage and change the resistor if you decide to use divided volts. on your XP45 when you get it. The frequency is more immune to noise than the voltage (and you don't really want to send raw voltages back to your control box).

Touching on the speed for a moment, LInuxcnc running with Mesa hardware has a servo thread that runs at 1 kHz and every cycle it calls all of the components that are loaded into the system by the hal file. If you can remember how to program in C, you can easily write your own components which then act exactly as if they are part of the core system.

Really whilst there are plenty of good working systems running linuxcnc, there has been a lot of work to take it to the next level over the last couple of years so that we have PID based torch height control and an internal THC tightly integrated to the trajectory planner rather than the more traditional up down bang bang style of up/down control you might find with masso or Mach3. Eventually, one of us will come up with a good stable working system that will find its way into the core code.

PhillC has a config he's working on called "Another Plasma Component" just a few posts down. He has the same plasma cutter as you. The catch is you need to compile it from source which might be a bit scary but he probably has the best chance of getting it into the source code becasue he's got it all up on git hub.

Tommylight also has a good system that has recently been adapted to use Mesa and the THCAD instead of the Proma150 he uses in europe.

BigJohnT also has a config which was probably the original mesa config.

Islander261 has got a good robust working PID based system that he says easilly exceeds the performance of his previous commercial controller.

I've been using an experimental branch that did not make it to prime time that uses the new external offsets feature now in master branch. Now I've upgraded to a Thermal Dynamics 120 amp system, I have it working quite well. Now I have to extend my config to use Ohmic sensing now I have a machine that supports it.

So welcome to the club, just focus on getting your machine moving first and then we'll help you with the plasma stuff.

Also, PCW from Mesa is a very active member and will provide outstanding support via this forum.
The following user(s) said Thank You: tommylight, Franklin

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16 Mar 2019 13:12 #128732 by andypugh
Replied by andypugh on topic New to all of this

rodw wrote: If you have a gantry machine, you are probably better off installing the development branch (We call it master). There is an ISO for it here:
www.linuxcnc.org/testing-stretch-rtpreempt/


That's actually the preempt-rt version of the current released version, not the development branch.

If the OP actually does have a gantry then we can give the instructions to get that version, but he might as well begin with one of the released versions. If he is looking at the Mesa cards then that link above is a good choice (newer OS, better hardware compatibility)

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16 Mar 2019 15:56 #128745 by JTknives
Replied by JTknives on topic New to all of this
Wow thanks guys.
My plasma table is a bit diffrent then other tables. Because of my space and what I’m going to be cutting I went another direction. I just have a single stepper motor for each axis. Thy are closed loop steppers becaus I tryied a standard style stepper and did not care for it. The Y axis is over hung and it mounts to the X axis only on one side. The x axis is at the back of the table and has 2 linear rails at 90° to each other. There is a bracket over the rail blocks and the end of the Y is mounted to this bracket.

Yeah I was looking at the THCAD and hoping I could build the control right into LinuxCNC. I figured I would be money ahead figuring the masso needs a THC added and that would put me in the 1k$ range for the masso and a decent THC.

So when looking for a computer to run this is there any that are better then others. I’m not looking to get the cheepest thing out there. I need a good LinuxCNC functioning computer first and I will deal with the price I need to pay.

Thanks agian guys

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16 Mar 2019 19:52 - 16 Mar 2019 19:53 #128763 by rodw
Replied by rodw on topic New to all of this
The PC I know that works is the USFF Gigabyte Brix with a J1900 or N3160 processor. But look with a similar PC with same chip with 2 NIC's one for mesa and one for internet. the included intel wifi has very high latency so you need to throw it out and add a wifi dongle for internet with the Brix. Make sure all power saving features are disabled in the BIOS.

Alternatively, if you have an old PC, try it. I have found 32 bit PC's are not good with the Mesa ethernet required PREMPT_RT OS>

As Andy has said, use that Linux Stretch ISO above, you don't need master branch yet but may need to upgrade to master branch down the track to get access to the external offset branch for THC control. That can be done from within the Synaptic GUI based package manager that will be on your system.

As long as your closed loop steppers are step and direction devices (which they are), the Mesa cards I mentioned are the right hardware.

Get your PC set up, sort out the latency and play with some of the included SIMS (simulators) that will work without attached hardware.
Last edit: 16 Mar 2019 19:53 by rodw.

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16 Mar 2019 20:08 #128766 by rodw
Replied by rodw on topic New to all of this
Fogot to mention to burn your ISO to a bootable USB stick the best tool I've found is w32diskimager on windows.

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16 Mar 2019 20:44 #128769 by JTknives
Replied by JTknives on topic New to all of this
I had noticed people mention thoes Computers. I did not know if thywhere used because thy where the cheepest thing that could run LinuxCNC or it was actualy a good computer for it.

Is LinuxCNC picky when it comes to brands of ram? Plan is to use an SSD as well. I have a few kicking around. I think I have an evo kicking around as well. Might just pull the one out of the ps3 as we don’t use that system anymore.

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16 Mar 2019 20:55 #128771 by rodw
Replied by rodw on topic New to all of this
LinuxCNC is not that picky but the smaller USFF factor machines have a lot of power saving features that can affect latency.

LinuxCNC does not put much strain on the hardware so a Celeron that these PC's have is a good choice. I Picked one based on a recommendation from PCW from mesa on this forum. I think he mentioned there is a Zotac with dual NICs and there are many like that on Alibaba/AliExpress in a fairly industrial config to be used as routers and the like.

Latency is an issue with parallel port systems as they step generation is done in software on a seperate base thread that runs much faster than the servo thread. Because the mesa cards do hardware step generation, the base thread is not required and latency requirements are much relaxed. If they had a parallel port, these would not be a good choice.

So LinuxCNC tells the MESA stepgen to generate steps at a given frequency. Mesa does this until its told to stop or change the frequency. Linuxcnc can tell it to change the frequency 1000 times a second.

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16 Mar 2019 23:14 #128780 by tommylight
Replied by tommylight on topic New to all of this

rodw wrote: ....... you don't need master branch yet but may need to upgrade to master branch down the track to get access to the external offset branch for THC control.

There is the THC version that works with any branch of Linuxcnc, even the very old ones, and works with THCAD also, so having external offset branch is not a requirement for THC.

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