On 2/23/25 10:39, Dave Engvall wrote:
This is all Gene’s fault. :-) His evangelism of steppers-servos has penetrated
my thick skull. Side note: tinyG has signal pickoff before the final stage so
it is possible to drive stepper servos off a tinyG.I’ve not gotten there yet
but headed that way. Of course “the difference between theory and practice….”
Be patient nothing I do these days is fast or efficient. Stay tuned!
D
On Feb 22, 2025, at 5:41 PM, gene heskett <ghesk...@shentel.net> wrote:
On 2/22/25 18:29, Dave Engvall wrote:
There is a method to my madness, to wit I really want to know how good, or bad
the tinyG is. Older version of the emc interp but a much faster cycle time.
Glass scales are problematic for velocity control but rather good for position.
Servos on that machine with good encoders on the ball screw were much better at
velocity control, roll that in with a glass scale for position and you have the
best of both worlds.
I've had very good results on the one machine I have converted to closed loop
stepper/servo's. Totally doing away with the PID's. Feedback is from the TP
that drives that axis, the stepper/servo's have their own PID's. My sheldon
rapids are 2x faster, and quite a bit more accurate. The TP outputs good code.
These motors stay w/in a count of error And it makes beautiful metal. Well
within the thousandths I wrote the code to do. No ticklish PID tuning ever, no
PID's to function as rubber bands, so what the TP spits out is exactly what the
motor does.
To explain that further, there are /PID's in the controller and an
encoder in the motor, but that encoder feedback is not given to
linuxcnc. That feedback to the controller serves to allow the controller
to do a couple things. The controller then knows where the motor is at a
considerably higher bandwidth than linuxcnc's 1 or 2 kilohertz servo
thread. If the motor is doing this w/o any great error, the motors
excitation current is minimal so there is no great heat. If the motor is
behind, the controller turns up the current until the motor is where its
supposed to be. By the same mechanism if the motor has overshot, the
controller will turn up the current AND step the motor backwards until
the motor is in position. Applied to a 3d printer, the motor can be 5 to
10x faster w/o a layer shift, which occurs if the motor has lost steps
and is no longer HOMED. This relative lack of burn your hand heating,
and the active motor control averages quite a bit less wasted power you
can see in how fast the power meter spins and because the controller can
use the full power supply output for maybe 20 microseconds, makes the
machine 5 to 10 times faster. Hanpose LC42 controllers can tolerate 90
or more psu volts to make a nema-17 motor do exactly what the TP told it
to do. The LC57 controller for Nema-23's is rated for about 110 volts. I
am using 72 volt psu's on one converted printer, not the usual 24 volts.
/
/I hope this is a better explanation. And helps to explain my enthusiasm./
On Feb 20, 2025, at 1:41 AM, Todd Zuercher <tzuercher1...@gmail.com> wrote:
If they are equidistant wouldn't simply use them the same as an ordinary
encoder index signed?
On Thu, Feb 20, 2025, 4:09 AM Andy Pugh <bodge...@gmail.com> wrote:
On 19 Feb 2025, at 17:15, Dave Engvall <dengv...@charter.net> wrote:
I think both have R marks at 50 mm intervals.
Seems logical?
There are systems where the index marks are at varying distances from each
other such that you know exactly where you are after seeing two marks.
There was discussion of this on the forum, which resulted in the homing
process being modularised, (HOMEMOD)
I don’t recall if we saw a suitable HOMEMOD module for this style of scale
in that thread.
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
Cheers, Gene Heskett, CET.
--
"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
_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
