On 3/28/23 15:31, Viesturs Lācis wrote:
Hello!
I am asked to retrofit some old 3 axis mill to LinuxCNC. It is not yet
clear if original servodrives are working or not, so the owner wants
to reuse Fanuc servodrives and motors they have removed from another
machine. This is label of the servodrive:
https://pasteboard.co/LNVjuaBYC3Ox.jpg
I have zero experience with Fanuc, so I am hoping for collective
wisdom to understand - is this a good idea?
My main concern is PID tuning in the drive. Do I understand correctly
that even with the original motor and cabling but different load it
will not be stable and reliable?
Or should I look for bigger stepper motors in case original drives have retired?
Viesturs
If the FANUC's can't be stabilized, I think I would want to stabilize it
without any pid's, driving the new stepper/servo's directly and let the
smart drivers sort it out. I am doing that 4 times here and its working
great. The first two are a 3nm rated nema 23 motor on the Sheldon's Z,
and a 1nm nema 23 motor on the back of a new front panel as an apron on
the carriage. Z can move around 120 ipm. X at 60+ ipm. With an rpi4
issuing the orders.
These new drivers cannot lose "home" w/o issuing an estop to linuxcnc.
I can position a tool to hit a chuck jaw, and run it into the chuck jaw
at 10 ipm from the keyboard, it contacts the chuck jaw, kills linuxcnc,
which at the same time kills motor power, the tool springs back from the
chuck jaw by 5 or 10 thou, and with my e-stop also killing all motor
power, and the drivers are reset by an F2 tap to re-enable the machies
power. The tool is not damaged and the chuck jaw is not marked.
re-enabling linuxcnc with a tap on F2, rehome it, fix whatever caused
the stop and run from line. But that stop has yet to occur in regular work.
I also have a 6040 gantry mill that came with junk electronics I tried
to make work, and finally tossed it all in the trash trailer, went to
retrieve the drivers from my defunct hf micromill, taking the xy drivers
from 8mm to 200mm top speed, but the Z motor had problems lifting the
heavier new 4 bearing water cooled spindle motor, so now a 1nm nema 23
stepper/servo lives on that mount and lifts that spindle motor at 20
ips. Then I needed a B axis to carve screws, had a ebay 5/1 worm, put a
3nm motor on it, printing the shaft adapter and chuck for the stick,
found a live center I could shim to the correct height. Its able to spin
the screw at several hundred rpm while carving the buttress threads,
tracking the Y axis motions to carve a 22" long screw with 2 start, 12mm
pitch, 4mm tall buttress threads with a 1/16" round nose sc tool at 18k
revs.
So I'm convinced that the new stepper/servos are the answer, so much so
that I'm rebuilding a pair if big 3d corexy printers to use them. Ending
layer shift because they lost home forever. They incorporate their own
PID and encoders are in the motors. They get to where the tp sends them
or stop lcnc. I might also point out that they are much more power
efficient, the error magnitude is used as the current to the motors
control and in normal operation, the motor temp rise is so low it will
amaze you.
YMMV, but that is my observations, we have a brand new team of well
trained horses to move our machinery.
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Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>
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