On Sun, 29 Oct 2017, Chris Albertson wrote:
Date: Sun, 29 Oct 2017 10:42:49 -0700
From: Chris Albertson <albertson.ch...@gmail.com>
Reply-To: "Enhanced Machine Controller (EMC)"
<emc-users@lists.sourceforge.net>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] Ethercat master (low latency)
On Sun, Oct 29, 2017 at 3:37 AM, Nicklas SB Karlsson <
nicklas.karlsso...@gmail.com> wrote:
Then of course he is uses an $8,000 servo controller to hit those
(x,y,z)
points so no surprise the circle is spot-on perfect.
I am always impressed when some one finds a way to do impossible things
with no effort.
To pay someone else to do work is a simple method to do things without
effort. Only problem is where do I get the money?
Try begging it is quite effective
For no money all you get is to read about great ideas which to me is most
of the fun.
Now the problem is I can't afford an $8000 Ethercat based servo controller.
But I wonder it the same principle can't be applied to any serial multi
drop bus? As long as there is a "master" that users a hardware clock to
shift bits out of a hardware buffer then it should work
Yes, the german guy in the video had a university funded system. Not many
of us can afford to buy what did. But as I just wrote above, i think
other buss types would work. Next I think it a good idea to study
CANbus. The so called "Controller Area Network" is cheap to implement and
logically is seems a lot like Ethercat.
I'd prefer Ethercat because every PC, Rasbury Pi and Mac has a built-in
Ethernet port so there is no hardware to buy and install but the slaves are
expensive.
Now that we have an "existence proof" I', thinking that
EMC/linuxCNC/MachineKit have partitioned the problem wrong and the result
is that it forces a requirement for hard real time to far up the chain.
OK, "wrong" is to strong of a word to fault the original designers. They
where working in a world where cheap micro controllers did not exist.
tour of the hardware <https://youtu.be/Ru9ylsm0uAA>
Using the hardware.
Here he uses a cell phone to measure table accelerating and at the end
mills a circle. 0.02mm eccentricity
linnuxcnc/ethercat demo <https://youtu.be/7kn-G5HFjD8>
As I said, cANbus might be a something for hobby level budget. I don't
know yet.
--
Chris Albertson
Redondo Beach, California
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A real time host is still needed for CNC coordinated motion with Ethercat
slaves. Ethercat does no change this at all. Laptops will work in some
circumstances but can cause troubles with multiple ms real time delays
when doing power management tasks.
Also RPIs are not good real time Ethernet masters for a couple of reasons
1. The Ethernet is routed through USB which has terrible real time
characteristics
2. The RPI is too slow to have decent real time network performance with
Preempt-RT
As far as LinuxCNCs architecture goes, keeping the real time portions of
motion in the host are required to retain the power, extensibility, and
flexibility of HAL, You can of course move HAL to a remote ucontroller that
supports floating point and dynamic object loading, but then you have two
OSes to maintain rather than 1.
Note the LinuxCNCs real time capability is what allows it to be a EtherCAT
master...
Peter Wallace
Mesa Electronics
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