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Thread: Guidance for Updated G0704 Electronics Design

  1. #13
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    Default Re: Guidance for Updated G0704 Electronics Design

    It all depends on latency... Yes - using mesa the latency doesn't have to be as good as if you are running the printer port lets say.

    printer port - you want latency <20us depending on the step rate you are looking for.
    Mesa or other external interface hardware. For a 1ms servo thread - you want to have <100us of latency. So better - but you still need good realtime response.

    Couple of thing to throw out there. If you are using mesa hardware (especially Ethernet solutions) You need to run the rt_preempt kernel - not the rtai kernel that comes with the live iso.

    A laptop may run rt_preempt just fine. I have a laptop here that I use for testing linuxcnc configs. It has really good latency numbers with rt_preempt as long as you don't a) mute the speakers or b) turn on the keyboard light. YMMV

    Getting LinuxCNC

    this explains how to install rt_preempt.

    If you want to go cutting edge - there is currently a livecd using debian stretch (latest released debian) with rt_preempt and linxucnc.

    Index of /testing-stretch-amd64-rtpreempt

    rt_preemt defiantly seems to run better on newer hardware. Isolating cpus also helps as stated above.

    Clear as mud?

    sam



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    Default Re: Guidance for Updated G0704 Electronics Design

    Quote Originally Posted by DJEkim33 View Post
    http://www.cnczone.com/forums/benchtop-machines/336478-cnc-forum.html

    This explains it all. But basically not everyone had good runout numbers with cheap ac bearings and you can find tapered roller bearings that are direct fit with less runout, less heat and they will not be your speed limiting factor.

    Thank you for the link. I was thinking tapered bearings on the X&Y ballscrews as the preload is very temperamental on the preload.

    I may also consider the spindle because I am getting some spindle run-out.



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    Default Re: Guidance for Updated G0704 Electronics Design

    Quote Originally Posted by samco View Post
    It all depends on latency... Yes - using mesa the latency doesn't have to be as good as if you are running the printer port lets say.

    printer port - you want latency <20us depending on the step rate you are looking for.
    Mesa or other external interface hardware. For a 1ms servo thread - you want to have <100us of latency. So better - but you still need good realtime response.
    I mentioned this in my post. My point was more don't waste time following along in the directions for the latency test as these try to optimize the base thread and for mesa you just need an ok servo thread which is very achievable with the boards I recommended.


    Quote Originally Posted by samco View Post
    Couple of thing to throw out there. If you are using mesa hardware (especially Ethernet solutions) You need to run the rt_preempt kernel - not the rtai kernel that comes with the live iso.

    A laptop may run rt_preempt just fine. I have a laptop here that I use for testing linuxcnc configs. It has really good latency numbers with rt_preempt as long as you don't a) mute the speakers or b) turn on the keyboard light. YMMV

    Getting LinuxCNC

    this explains how to install rt_preempt.

    If you want to go cutting edge - there is currently a livecd using debian stretch (latest released debian) with rt_preempt and linxucnc.

    Index of /testing-stretch-amd64-rtpreempt

    rt_preemt defiantly seems to run better on newer hardware. Isolating cpus also helps as stated above.

    Clear as mud?

    sam
    This is not entirely accurate as the 5i25/7i76 combo works just fine with rtai kernel. You may be confusing the need to switch to rt-preempt if you go with a 7i92 etc. As I mentioned the 5i25 and building a pc, installing the recommended wheezy iso that will be the simplest way to go as it uses the standard RTAI. He already stated his laptop did not have favorable latency. I am trying to save him the trouble of poking around with a bunch of different computers focused on the wrong stuff, which is what I did. You need to remember that the OP has no Linux experience and jumping right into different versions with new kernels and "you can use a laptop if you do all this" is not going to be useful. In fact I would say that its this type of stuff that actually scares people off Linuxcnc. It gives the impression that to make a functioning system you have to understand 100% everything in all those links you just posted. As he is new I am trying to point him in the simplest cheapest way to get started and be reliable, not worrying if his speakers are muted or the keyboard light is on.

    As for the original post I did miss that you wanted to go with a ethernet based setup. But in defense of the 5i25/7i76 combo, they do use a db25 to go from the card to breakout board but the 5i25 connects to a pci slot so its not a system based on the pc's parallel port and thus will function much better.



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    Default Re: Guidance for Updated G0704 Electronics Design

    I have no issues on the x and y using AC bearings and would stick with them. My complaint with AC bearings is just on the spindle.



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    Default Re: Guidance for Updated G0704 Electronics Design

    Quote Originally Posted by DJEkim33 View Post
    In fact I would say that its this type of stuff that actually scares people off Linuxcnc. It gives the impression that to make a functioning system you have to understand 100% everything in all those links you just posted. As he is new I am trying to point him in the simplest cheapest way to get started and be reliable, not worrying if his speakers are muted or the keyboard light is on.
    Yes, so true!!! I have spent my very small windows of available free time (I have 4 kids under age 8, my only free time is from 11pm until I get too tired to stay up) over the past week trying to learn more about LinuxCNC. My single biggest 'gripe' about LinuxCNC is that the development community has not spent enough time to simplify it for the general public to consume...probably since there is no marketing department or financial incentive to do so. That being said, the more I learn about it the more I like it and I have all but committed to go this route for my CNC build. Heck, I even know what "sudo" means now!


    I found out that installing the 'Ubuntu 16.04.2 LTS desktop' distribution as my OS was a waste of my time since the installation of the LinuxCNC *.iso file actually installs the 'Debian Stretch' distribution as the OS. I swear that nowhere does it say that the standard LinuxCNC download comes with its own operating system. As a side note, for a bunch of software nerds developing a kick-butt CNC machine controller, they REALLY SUCK at developing a user-friendly web page! And, it turns out that you can install it on a much older version of Ubuntu (version 12.04, aka "Precise Pangolin") but it also looks to be a more difficult installation. I'm in no mood to mess with RTAI (Real Time Application Interfaces) Linux kernel patches to get stuff working right now.

    I was able to actually play simulations with it after the full install (rather than running it off the bootable USB drive) and the flexibility and options are quite impressive...especially for someone who doesn't even know what they are looking at! Unless there are better suggestions, I will plan to buy or build a dedicated simple single-core desktop computer with a relatively small solid state drive and 1Gbs network interface card to be the host computer for LinuxCNC. I don't need to build any fancy integrated controller contraption with a touchscreen, I am perfectly content with a computer, monitor, keyboard, mouse and an RJ45 cable strung to a separate box that will house the machine controller board, drivers, power supply, etc. Question...
    1. I have seen several options for motherboards and computers as LinuxCNC hosts, are there any 'no-brainer' low cost used business/government surplus computers off eBay that I should just buy and be done with it?


    As far as controller boards go, I think the Mesa 7i76e board seems to be the ticket since I can connect to my [soon to be acquired] dedicated LinuxCNC computer via RJ45 ethernet cable. Questions...
    1. It appears that this card already has the ability to connect to up to five motor drivers, I don't need a break-out board (BOB) then, right?
    2. If above is true, if I wanted to, could I still attach the nifty C35 Quick Setup BOB via DB25 cable to simplify the wiring to the drivers in my controller box?
    3. Is there any other Mesa card that I need to or should just buy while I'm at it?


    As far as motors go, I am leaning towards the LiCHUAN closed-loop hybrid steppers. In my research on this topic I have found another set of confusing terminology in this industry. It seems that quite a few people on the interwebs incorrectly refer to their closed-loop stepper motors as 'hybrid' stepper motors, while in fact they may not be hybrid. It seems that the 'hybrid' stepper is actually a particular design combination of variable reluctance and permanent magnet motors, separate from being closed-loop. Questions...
    1. LiCHUAN offers both a two and three phase motor design option (not to be confused with the phase of AC power). I assume the three phase is better, but is it worth the extra cost?
    2. I have read that it is very important to choose the correct size motor for the application (not too small, not too big). The HOSS plans suggest a 570 oz-in motor for X and Y and a 906 oz-in for Z. I have also read that hybrid steppers have a different torque curve than standard steppers. Should I go with lower torque motors for the LiCHUAN hybrid steppers or just get whatever is closest to the HOSS plans?
    3. These motors look like they have a 5 or 9 pin serial cable for the encoder signal. Do these just connect back to the appropriate driver for that motor, or is it more complicated and I would need a MESA daughterboard or something that I would need to hook them up to the 7i76e board to close the loop?


    Thanks again to all of you for suffering my ignorance, this information is really helpful! Maybe it will help somebody else out as well.
    v/r,
    JJ



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    Default Re: Guidance for Updated G0704 Electronics Design

    Quote Originally Posted by JJ0704 View Post
    1. I have seen several options for motherboards and computers as LinuxCNC hosts, are there any 'no-brainer' low cost used business/government surplus computers off eBay that I should just buy and be done with it?

    There are a few you can look at. I used an Intel D525mw which were commonly used in schools and businesses. Integrated graphics card and very low profile. Got mine for $25 shipped off ebay. Just need a case(or put it inside with the rest of the electronics), pico 60w power supply, RAM and an SSD. All totaled mine was $80 with a wireless card.
    Intel D525MW Dual Core Atom CPU D525 1.8Ghz Mini ITX Motherboard Intel | eBay
    Here is a list of computers that do and do not work based on latency, which is not a big issue with your mesa card plan:
    LinuxCNC Documentation Wiki: Latency-Test


    Quote Originally Posted by JJ0704 View Post
    As far as controller boards go, I think the Mesa 7i76e board seems to be the ticket since I can connect to my [soon to be acquired] dedicated LinuxCNC computer via RJ45 ethernet cable. Questions...
    1. It appears that this card already has the ability to connect to up to five motor drivers, I don't need a break-out board (BOB) then, right?
    2. If above is true, if I wanted to, could I still attach the nifty C35 Quick Setup BOB via DB25 cable to simplify the wiring to the drivers in my controller box?
    3. Is there any other Mesa card that I need to or should just buy while I'm at it?


    The 7i76e is an FPGA and breakout board in one. As i understand it it will handle the step generation and I/O (input/output) functions that you would want a breakout board for. You could use the C35 but you really don't need most of what it does. Why woud you want the C35 also?
    As far as other mesa cards I am not as familiar with the 7i76e and use the 5i25/7i76 combo. Which is fine for what you are doing, is very well supported and is what most folks are using who are converting to Pathpilot which is the Tormach Linuxcnc based controller. I know you want an ethernet connection but there will be no speed difference for one combo over another in your situation. The 5i25/7i76 does use a db25 but it is not a parallel port connection like you may assume. The 5i25 goes into the pci slot of the computer and is your FPGA (generates steps instead of the computer) the 7i76 is a breakout board and connects to the 5i25 through a db25 cable(not the computers parallel port). Really not much difference between the two setups but you will see more 5i25/7i76 in the hobby community.

    Quote Originally Posted by JJ0704 View Post
    1. LiCHUAN offers both a two and three phase motor design option (not to be confused with the phase of AC power). I assume the three phase is better, but is it worth the extra cost?
    2. I have read that it is very important to choose the correct size motor for the application (not too small, not too big). The HOSS plans suggest a 570 oz-in motor for X and Y and a 906 oz-in for Z. I have also read that hybrid steppers have a different torque curve than standard steppers. Should I go with lower torque motors for the LiCHUAN hybrid steppers or just get whatever is closest to the HOSS plans?
    3. These motors look like they have a 5 or 9 pin serial cable for the encoder signal. Do these just connect back to the appropriate driver for that motor, or is it more complicated and I would need a MESA daughterboard or something that I would need to hook them up to the 7i76e board to close the loop?

    JJ
    The 2 and 3 phase will have different torques and more importantly they have different number of steps per revolution. Stick with 2 phase and you will be fine as they are 1.8 degrees per step and that is what Hoss's plans call for. The 3 phase are 1.5 degrees per step and you would need to rethink your ball screws.
    As for torque the Lichuan are rated in Nm so you will need to convert those numbers to find one that works. It looks like they have a nema 24 that is 4.5Nm which is 637 oz in and a nema 34 that is 6.5Nm (920 oz in). The encoder on the motor goes to the driver which will track the position. The driver will send the breakout board (7i76e in your case) a fault signal if it does not perform the move commanded. To get it all working you will have 3 sets of step/dir signals out of the 7i76e, one for each driver. And the drivers will each send a fault and move complete input signal back to the 7i76e that will go into one of the input slots of the card. There is no need to read the actual encoder values in Linuxcnc, you just need to know if the motor did not do what it was supposed to, the driver will use the encoder to achieve the move on its own. The closed loop will be a bit harder setup then the open loops but its manageable and if it gives you trouble you can leave the fault and move complete signals alone until you become more familiar with Linuxcnc hal files.

    All good questions though and I know how you feel about your time constraints. I have 5 kids and sneak my cnc obsession in whatever block of time I can find. For linuxcnc this is a good set of documents to read to get you started, just remember that with a mesa card some of it does not apply. LinuxCNC

    Mike



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    Default Re: Guidance for Updated G0704 Electronics Design

    I think I have found a candidate eBay cheap-o PC with a J1900 processor that might work. It is impossible to determine the details of the specific motherboard in it since I don't have the serial number of that particular machine, but I'll assume that whatever it has it will be possible to isolate down to a single core. Hopefully using the 7i76e Mesa card should make whatever latency it has acceptable.

    Plus, I'm going to buy one of these, just because they are so darn cheap...might come in handy someday if I decide to convert to an all-in-one enclosure.

    Quote Originally Posted by DJEkim33 View Post
    Why woud you want the C35 also?
    Only because it makes the driver wiring easier and 'cleaner' looking (and its only $38). You just plug this C34KL adapter into your driver, then just hook them up with a short RJ45 patch cable.

    Next step is getting a quote for the closed-loop hybrid steppers and drivers.

    JJ
    p.s. - thanks for the links...very helpful!



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Guidance for Updated G0704 Electronics Design
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