General Computer & Hardware Components Required?

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10 Sep 2016 15:40 - 11 Sep 2016 13:42 #80298 by gismofx
I'm in the process of designing a 3-axis gantry-type machine. I've been going in circles with hardware setups and looking for some answers as there seem to be more options and hardware and things seem to be changing quickly.

I'm trying to work to a reasonable budget and keep components simple-ish.

I'm looking to use something like this forr the computer: Intel Motherboard BLKD2550MUD2, Atom Dual Core 2500 NM10 mITX 2xSODIMM DDR3 LVDS+DVI+VGA+LPT, PCI, 4/3 USB2, GBLAN

and something like this for motion:
DMM AC Servo Kit

FYI,I don't want/like steppers.

From what I understand about the Servo options, there are two basic options(correct me if I'm wrong)
  1. The stepper-type that do step-direction(As I understand, this isn't a FULL feedback loop back to the controller. The servo motor has internal feedback loop to itself.) With these servos, I couldn't truly synchronize two servos for something like Rigid Tapping or Lathe Threading
  2. The real deal servos where encoder signals are fed directly into the controller(linux cnc). Fully closed loop. Servo Synchronization, position feedback, etc.

I'm looking for option 2.

Aside from any peripherals and bonus IOs and whatnot, generally speaking, what hardware is required to get linuxCNC to control the servos with full feedback? Is there some complete kits? Do I need a PCI card or only onboard parallel port? What's recommended here? Mid-Low cost.

TLDR; Starting from scratch, what hardware components are required end to end for a 3-4 axis full feedback servo setup to get up and running from nothing?

Thanks for you guidance.
Last edit: 11 Sep 2016 13:42 by gismofx.

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12 Sep 2016 00:26 - 12 Sep 2016 00:28 #80350 by tommylight
As far as i understood you, you are looking for MESA cards and servo drives so the control is fully on Linuxcnc side. They have a lot of options so be sure to have a look.
As for rigid taping, you need the control for spindle also with at least 1 encoder phase and index.
Almost forgot, PICO systems has systems and drives for servo control by Linuxcnc.
Last edit: 12 Sep 2016 00:28 by tommylight. Reason: added more info

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12 Sep 2016 01:18 #80351 by gismofx
Thanks. I looked through the Mesa boards and don't even know where to start... I suppose I need to find some servos first so I know what Mesa drives I need? Is there a source for new low/mid cost servos performance servos that will work with Mesa?

Seems like the DMM kit is not what I need?
Something like these will work with Mesa instead of the DYN4 Drive?www.dmm-tech.com/ac_servomotor_main_a1.html

Do I need a Mesa PCI card too?

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12 Sep 2016 01:33 #80352 by tommylight
It is a bit to much at first but let it sleep for a night and have a look again, the info on Mesa will start to fall into its places and all will be clear. They have servo drives that are pretty flexible at driving servo motors of different types, but i am not qualified to answer that, so i will leave that to PCW or other more experienced users of this forum.
That DMM setup you linked to, looks quite nice, but i would not recommend investing all that money for a beginner. Then again, any servo system will cost near that sum, so the choice is yours.
On the stepper side is the cost, and they do work as most of us use them every day all day, i do on several machines. Again just my thoughts, your choice.
That motherboard looks rally nice and cheap, even though it is yet to be known what latency numbers would come out of that.
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12 Sep 2016 12:15 #80358 by andypugh

From what I understand about the Servo options, there are two basic options(correct me if I'm wrong)
  1. The stepper-type that do step-direction(As I understand, this isn't a FULL feedback loop back to the controller. The servo motor has internal feedback loop to itself.) With these servos, I couldn't truly synchronize two servos for something like Rigid Tapping or Lathe Threading


LinuxCNC can do rigid tapping or lathe threading with both servos and steppers. The feed is slaved to the spindle encoder.

It is possible to have a fully-closed servo-loop with step-dir type servos. You simply view the step-rate as a velocity command and use a velocity-mode stepgen in LinuxCNC. The rest of it looks much the same as an analogue servo setup, with a PID loop comparing actual and commanded position.
But as such systems are closing thir own position loop in the drive, it it also perfectly possible to drive them in position mode. The loop is still closed, so you still have the servo advantages. However you can't do the advanced things that are possible when the loop is closed in LinuxCNC, such as velocity feedforward or using halscope to tune the loop.
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12 Sep 2016 16:12 #80367 by gismofx
Thanks. Yes, I want to fully close the loop with LinuxCNC.

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13 Sep 2016 01:51 #80376 by gismofx
I'm slowly absorbing:

Would I need something like this to start:
MESA 7I77-5I25 PLUG-N-GO KIT

Then, I can use either Mesa Drives or other Servo Drives that are paired with a Servo? Or Is that overkill? Is there a better way? Would the DMM servos work? Can anyone suggest some comparable servos to look at aside from DMM?

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13 Sep 2016 07:55 #80380 by andypugh
7i77 and the DMM Dyn4 drives are a good match.
The analogue input for the Dyn2 drives is 0-5V and runs full-speed if disconnected, so is not a very good way to control those drives.
Dyn2 + step-dir control with encoder feedback to LinuxCNC can work, for that something like the 7i85S would be used. The 7i85S does not offer dedicated GPIO so you would need to add one of the smart-serial boards on the serial-port connetion of the 7i85S: store.mesanet.com/index.php?route=product/category&path=83_88

You should also look at Pico Systems and General Mechatronics.
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16 Sep 2016 21:36 #80506 by gismofx
I've ordered the mobo, power supply, 4 gigs of ram(because it was cheaper than 2 in most cases) and other bits to get the computer going. I'm going to install LinuxCNC and try the demo. I'm still looking for some comparable servos and drives like the .75kw + DYN4 in terms of performance and price. I may just pick up one set and give it a test.

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20 Sep 2016 00:33 - 20 Sep 2016 00:40 #80645 by gismofx
I pulled the trigger a bit too quick.. The Atom Board I picked, while cheap and seemingly has plenty of power, uses an unsupported graphics chip which would really limit the whole experience. Also in my research, I guess I don't need the lowest latency possible because I'm not doing software stepping/control and using the mesa card for the servo control instead. I relaxed a little on trying to find the fastest/cheapest/fanless setup(if that even exists).

There are numerous discussions on that video chip. Here's just one: forums.linuxmint.com/viewtopic.php?t=105091

I returned the components and ordered an AMD Athlon 5350 and Mini-Itx board with 8 gigs of ram for under $100. It has better components, USB3 and HDMI out which will make monitor selection a little easier these days. Downside is it's not fanless. I'll keep poking around for a nice fanless setup, but for now, I have an inexpensive setup to start playing with.

I may try this: 5350 Fanless Cooler
Last edit: 20 Sep 2016 00:40 by gismofx.

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