Looking at the math some more, it seems like Sebastian's suggestion
really ought to work.  It seems like I should be able to do something
like this at the end of my code before looping back to the beginning:

#<oldx> = [#<_x>]
#<oldy> = [#<_y>]
#<theta> = [[atan[#<_y>]/[#<_x>]] + 90.0]
#<x> = [cos[#<theta>]]
#<y> = [sin[#<theta>]]
G1 X#<x> Y#<y>
G10 L20 P0 X#<oldx> Y#<oldy>

That G10 L20 doesn't seem to be doing the right thing though.  Printing
out coordinates looks good, but when it wraps around to the beginning
it seems to go to some gigantic coordinates out of range.

-- Ralph

________________________________________
From: andy pugh [[email protected]]
Sent: Friday, March 16, 2018 1:00 PM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] joint/axes question (2.8-pre)

On 16 March 2018 at 19:29, Ralph Stirling <[email protected]> wrote:
> This offset approach is proving harder than I expected.  I think it is 
> because I'm
> using the PID-driven stepgen approach generated by pncconf (7i92 board).


Ah, yes, that will make things harder.

You could try using a conventional non-PID setup, those always used to
work pretty well, if not quite so well as the PID based one.

> I think the velocity gets messed up by the step function in position,
> and the pid loop is using velocity.  Any further suggestions for
> achieving my invisible 90 degree rotations?

You could put a limit3 component between the G-code output and the
offset input. That would remove the step.

--
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, 1916

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