Spindle Step/Dir servo ramp down before stop on M stop command.

Is it possible to do a full re-home on the C axis when returning to Axis mode?

I don't know -
Perhaps like this:
In M101 mode - When HOMING - HOME C 'status', and DRO.
Then when going M100, first rotate C till index, zero encoder counter, then rotate to commanded angle ( zero in this case, after homing)
Then, after a Gx Cxxx position command, if exiting via M101, and running the spindle, and the going back into C axis mode with M100, first rotate C till index, then zero encoder count, then rotate to original commanded C axis position...

I wonder if some of the behavior is motor drive related, that is, does the drive "remember"
its position when disabled?

No, the drive and motor is dumb - it is basically just a stepper that does not lose steps ( within reason..)

Ok for you and Andy, I did a few Halscope plots - that is tedious! Transfer the log file windows, excel, screen capture, etc, etc..

I set up the scope to capture:
axis.c.pos-cmd
hm2_7i92.0.encoder.00.count
hm2_7i92.0.encoder.00.position

I also opened a few Halmeters:
hm2_7i92.0.encoder.00.position
hm2_7i92.0.encoder.00.count
pid_c_command
pid_c_feedback

Procedure:
After starting LCNC I HOME_All, then the column 'user input' are the commands/mouse clicks I execute.
The resulting values of the parameters are then shown the the same line as the user input, for that input.

Can you clarify the current status:
Position mode works OK if the lathe hasn't been used in lathe mode
After using lathe mode, position mode sort-of works, but takes a very long time and many oscillations to settle?
I am not clear if jogging works in position mode. (Do you see the DRO angle change if you jog?)

Sorry for obfuscating thigs so badly - I had indicating the status in detail in posts about 6 or 8 previous, but its lost in the verbose detail...

In summary:
The very first M100 C axis enable followed with a move > 30 deg or so ,after HOME cmd, can be unstable - not always, but often.
ANY move after that, with M100 active, is ALWAYS stable, clean and critically damped.
If you disable the axis (F2) and move it, or M101 and run the spindle with M03 Sxxx, then M05, then M100 again, it will oscillate till at position - for seconds. Thereafter, as above, ALL further moves are stable and clean.
(NOTE - I have tamed that oscillation with your suggestion of pid.c.maxoutput = 5, and increased max_vel and max_accel., but this is just masking the issue).

WRT jogging.

After HOME-ING (all) , X and Z jog correctly ( jog wheel, AXIS mouse button, User pushbuttons)
C does not jog, C DRO does not change - C at this point is in M101.

THEN, if you go M100, none of the axes jog anymore - no jogwheels, no user jog buttons work.
However, ( in M100 say) if you use the mouse and jog X or Z momentarily on the AXES screen jog buttons, the axis jogs and THEN all the jog wheels and user pushbuttons work again - including jog C axis , if in M100.

THEN, if you do M101, the jog no longer works again. But do the AXIS screen button jog trick with X or Z again, and all works again...

1. Encoder counts are not used so there no point in plotting them.
really only interested in encoder position (position feedback)
and position command

2. Not sure why the spindle position is scaled, this makes it hard to
interpret what's going. Its certainly not needed for a normal C axis,
and since the motion issues are all on Axis mode. this part should be as straight
forward as possible. Scaling the spindle speed for spindle mode
has fewer side effects

PCW wrote:

1. Encoder counts are not used so there no point in plotting them.
really only interested in encoder position (position feedback)
and position command

2. Not sure why the spindle position is scaled, this makes it hard to
interpret what's going. Its certainly not needed for a normal C axis,
and since the motion issues are all on Axis mode. this part should be as straight
forward as possible. Scaling the spindle speed for spindle mode
has fewer side effects

Ok, so are those plots useless? I am as I stated often, not familiar with all the syntax, parameter names, etc - I am learning, but ..

You asked for halscope plots of encoder position and commanded position - no mention of 'feedback' there so I can maybe be forgiven?
I will redo as needed, - can you be specific as to what parameters I should plot?


The spindle position scaling - All the CAM programs I have used ( BoBCAM, ECAM, SpruteCAM, all command C axis on a lathe in degrees - the G01 Cxx are xx i\n degrees, so the units of 0 to 1 in LCNC meaning 0 to 360deg is not of much use...

....and since the motion issues are all on Axis mode

- I don't know what that means..

encoder position is the feedback position

If the C axis were scaled in degrees (which would be standard)
The encoder position would match the commanded position, making it easier
to see what's going on. in Axis mode (you have two modes, one I would call
axis mode and the other, spindle mode)

If the axis is scaled in degrees you would need to scale the feedback
to LinuxCNC in rotations for spindle mode. But spindle mode is much
simpler, you don't even need PID

I do think that you need somehow to do what linuxCNC does when it first
initializes an axis: set its joint commanded position = to the joint feedback
position so there is no jump when changing modes. I dont know if this
happen when you re-home an axis or if you can programmatically
force a re-home

Forgive me, I am somewhat confused...
You stated:
2. Not sure why the spindle position is scaled, this makes it hard to
interpret what's going.

And now you said:
If the C axis were scaled in degrees (which would be standard)

The C axis IS scaled in degrees, or at least that's my understanding - I command it with Gx C(degrees)
My understanding is that 'spindle position' and 'C_Axis position' is the same thing in M100 ( C axis enabled mode) - the angle that the encoder on the spindle has been rotated to.
C_axis mode, which I believe you refer to as Axis mode, which I enable by means of an M100 code, IS scaled in degrees.
And then Spindle mode is the non-angular spindle mode, ie, exit from M100 mode with a M101 command, at which point a spindle-on, speed command - M03 S1000 - would turn on the spindle at 1000rpm.


2. Not sure why the spindle position is scaled, this makes it hard to
interpret what's going. Its certainly not needed for a normal C axis,
and since the motion issues are all on Axis mode

So, I don't understand that statement , what 'spindle position' means since I thought the spindle has no position in 'Spindle mode' - it just turns at a commanded speed...And therefore I am not aware that it is scaled..
Also I thought you said If the C axis were scaled in degrees (which would be standard, but then say Its certainly not needed for a normal C axis,

I have a headache..!

Sorry, battling to understand this stuff!

Edit:
WRT the parameters to plot -
'encoder position(feedback position) and commanded position'
Do you mean pid.c.command and pid.c.feedback?

The spindle in not natively scaled is degrees, its been patched with the scale component.

I guess what I am saying is it looks like a C axis mode was added to the
native spindle mode (which is scaled in turns) rather than starting with a C
axis and adding the simpler spindle mode.

If the Axis mode was the native mode, the only external scaling applied would be in the
spindle mode (multiply the position in degrees by 1/360 to feed to LinuxCNCs
spindle.0.revs pin when running in spindle mode) This means in axis mode the joint
position command and joint position feedback are both in degrees. (and FF1=1.00)

PCW, Thanks for trying to get me to understand things!
It is not easy for me I fear - I used Stepconfig and Pnconfig to define a setup for a benchtop mill and a gantry router - that worked fine, was easy, but that method isolates me totally from the guts of the thing - nothing to fiddle with in the HAL/ini files so one learns nothing.

This lathe is very complicated for me. The basic lathe was complicated by the use of a step/dir servo for the main spindle drive. That required step pulse manipulation for the M05 type command to not bang the spindle to a halt from 2500rpm - I am not capable of implementing that sort of function as I know far to little of the software system and its innards. Andy kindly assisted with that. And then the basic lathe (2 axis) worked, and works nicely.

If I could not implement the step pulse control myself, for the decel control, there is no way I will manage the C_axis, and so I rely on the goodwill and kind assistance of people like you and Andy. I have no option. But that means that if you wish to assist, you have most of the work to do. I work very hard at researching and digging into what has been suggested to try understand how it works, what it does, and how the hardware and software tie together. But I can only do so after the effect - I cannot invent the solution -
Perhaps in due course, if the solution begins to solidify, I can learn from it and begin to understand better, but at the moment I remain un-enlightened, and trying.

The spindle in not natively scaled is degrees, its been patched with the scale component.
Again, I am unaware of what was done here, my understanding is that the
spindle mode ( normal 2 axis lathe spindle M03 Sxxx) is left untouched, but in C_Axis mode ( M100, C_axis enabled), the Gx Cxxx commands are scaled to be in degrees, not units of 1. Obviously I have not understood this correctly, but cannot fathom what goes on here, and how it links to the rest of the control:

net c-pos-cmd => pid.c.command
net spindle-revs scale.degrees.in
setp scale.degrees.gain 360
net spindle-degrees scale.degrees.out => pid.c.feedback
net c-output pid.c.output => mux2.0.in1

To me there are many mixed things here - spindle-revs appear to be scaled in degrees, etc, and I am lost ...

If the Axis mode was the native mode, the only external scaling applied would be in the
spindle mode (multiply the position in degrees by 1/360 to feed to LinuxCNCs
spindle.0.revs pin when running in spindle mode)

Again, I have no idea how to do that - I followed Andy's guidance - As Andy said, he is also learning with this implementation - if there is a more appropriate and correct method, could you provide an Implementation to get us going?

If the axis is scaled in degrees you would need to scale the feedback
to LinuxCNC in rotations for spindle mode. But spindle mode is much
simpler, you don't even need PID

I do think that you need somehow to do what linuxCNC does when it first
initializes an axis: set its joint commanded position = to the joint feedback
position so there is no jump when changing modes. I dont know if this
happen when you re-home an axis or if you can programmatically
force a re-home

Where can we start to actually implement this concept, together with all the other bits - Servo speed control during spindle stop, etc?
I am willing to start from scratch as many times as it takes!
But I do need a clear setup, eg, a defined HAL and ini file, that implements the concepts. Then I can test, and try understand how to make it work.
That means the folk who wish to help me are going to be harassed even more by me, and I do not wish to annoy more that I already have..