On 1/4/26 00:27, andrew beck wrote:
hmm
just read the link again to the example posted further up the email chain
yeah it's going to a sum component
ok i understand this i think
i will try hopefully in a couple of weeks
cheers
Andrew
Better yet guys, change the stepper to a closed loop stepper/servo &
bypass the PID.
The closed loop stepper/servo does precisely what the TP issues, and if
the drivers
are from Hanpose, the loop is one micro-step tight because you can pull
the 24 volt
supply which is limiting the rapid speeds and use 72 volts. That motor
isn't going to
move a micron w/o the driver doing what it needs to make the motor do
precisely
what the TP asks it to do. Even with only 42 volts, my Sheldon's rapids
doubled in speed.
These drivers also have an output you can feed into the e-stop logic to
stop LinuxCNC
in its tracks if the motor loses home.
Thoroughly tested, never happened while making swarf.
Yeah it costs a wee bit more per axis, but its absolute peace of mind.
The PID is
internal to the driver, an LC42 for 3d printers, an LC57 for nema 23's,
up to 3NM.
Motors run cold unless you are pushing it too fast for making swarf. My
B axis
motor on my rebuilt (I threw the electronics away & redid it with
LinuxCNC) 6040
mill runs at 3000 rpm while carving a vise screw, runs warm but not burn
your
hand hot. Does exactly what the TP tells it to do.
I'd post pix to prove it but JK won't let me.
On Sun, Jan 4, 2026 at 6:29 PM andrew beck <[email protected]> wrote:
hey stuart
yeah the ballscrew is connected both ends. i think one end has the big
angular contact bearings etc
and the other only has deep groove ends probably (its much smaller than
the driving end)
on my other two cnc mills they have angular contact bearings both ends and
the screws are stretched between them slightly with a tiny bit of preload
hey guys
i was reading the link that sam sent two and it looks like the two Pid
loops are running side by side and then the outputs are added together
before going to the servo drive
would i be correct in thinking that they are using the "sum" component in
linuxcnc to do that?
if so this is getting pretty simple
cheers
andrew
On Fri, Jan 2, 2026 at 3:07 PM Stuart Stevenson <[email protected]> wrote:
HI,
I don't think the LinuxCNC control scheme is cascaded or nested. I would
call it parallel.
The only backlash problem I can imagine is if the backlash causes the
motor to dither trying to maintain position because cutting forces move
the
axis enough to cause the control to try to correct the axis position.
Is the ball screw supported on each end? If it is, then, is it possible
the screw has some stretch preload.
regards
Stuart
On Thu, Jan 1, 2026 at 4:10 PM andrew beck <[email protected]>
wrote:
hey guys
sam i just looked at that link you sent
that looks pretty cool
only thing is i don't know is if it will work to reduce the backlash
issue
i am getting. I have about 0.10mm of backlash on each axis. half of
that
is from the thrust bearings which is fixable with new bearings
the rest is from the ball nut i think and i am not willing to fix that
but i can only try it.
does anyone want to have a go with making a config like they did? one
axis
would be best I am struggling to get my head around the different
layers.
i probably need to write it all out or use a diagram or something.
regardless i am sure i will work it out. just might take some brain
cells
cheers
Andrew
On Fri, Jan 2, 2026 at 4:54 AM Sam Sokolik <[email protected]> wrote:
This was also John k.. I would trust his solution. He is the one
that
came up with hal in linuxcnc... (Among other things).
On Thu, Jan 1, 2026, 9:49 AM andy pugh <[email protected]> wrote:
On Thu, 1 Jan 2026 at 15:41, andy pugh <[email protected]> wrote:
On Wed, 31 Dec 2025 at 22:14, andrew beck <
[email protected]>
wrote:
just looking for a config example if possible for a mesa card
from
someone
that has this nested PID loop setup.
This may not be as effective as you would hope. Cascaded PID
loops...
Actually, what was done with the MPM jigmill wasn't a cascaded PID.
What was done there was to run a P + FF control based on the motor
encoder and an I control based on the linear scales.
Then the two controllers were summed together to create a PID
controller, but with I using a different feedback source than P and
D.
--
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1912
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