On 9/28/26 19:36, Peter Wallace wrote:
On Mon, 28 Sep 2026, Chris Albertson wrote:
SOme math? moving at 200mm per second a 10ms uncertinaly is a 2 mm
error. That is not even close to acceptable. Wht they do is (1)
have 1000x better timing and (2) after finding the approximate
location, back off and move very slowly to find the exac point.
On Sep 28, 2026, at 1:28?PM, Peter Wallace <[email protected]> wrote:
On Mon, 28 Sep 2026, Chris Albertson wrote:
Realistically, no one is going to redesign LCNC to use target
times. It would be too large of an effort relative to the size of
the project.
Why would you? since it would result in the controller losing the
ability to react in real time to external inputs.
The way it works is that ther microcontroller has hardware that
samples a local clock when a pin changes. Sp by moving the timing
out to the microchtroller you actually gain real-time precision. It
is easy to get micosecond level timing. Lets say you start. hardware
counter running at 1MHz and then tell the hardware to capture the
count when a limit switch pin changes. You can now react to that
real-time even in a micro second. Linux could never by so fast. I
didn?t invent this. It is why many micro contreoller have this
hardware for stuff like this.
From linux?s point of view it is the idetical same thing, it get
notice that a limit switch is closed but now alomng with that notice
is the exact microsecond when that happened.
This is already done with many LinuxCNC I/O devices, what LinuxCNC
does not do
is buffer commands and data as this prevents real time control reactions.
The fact that a peripheral can react quickly is not useful in many
motion contexts as it affects motion planning for all axis, the
controller must react quickly...
Which, from my personal experience with the closed loop stepper/servo's
is fast enough to prevent broken chips or marks on the stationary chuck
jaw it ran into, creeping slow or at 60 ipm. The tool contacts the chuck
jaw, Z stops and this turns off the driver's output bugs and I have that
signal wired into the E-Stop which crowbars the lathes AC input,
shutting everything down in its tracks. Tool chip is not damaged & the
shutdown kills the PSU's allowing the drive train to unwind far enough
to slip a 10 thou feeler blade between the chip and the chuck jaw that
stopped it. This "test" has been done at least 100 times while I was
trying to impress visiting frogs. Pull the tool holder off the QCTH, F2
to repower the lathe, rehome the lathe, put the tool holder back on and
continue the job. All this with an rpi4, a 7i90hd and a trio of 7i42's
needed to make the 7i90HD survive in a 5 volt world. Not cheap, but
sure works nice.
This is due to Peter W. and others who designed the stuff to make it
possible to do it with a pi. You know who you are and gave me lots of
help to make it happen. Thank you ALL.
Cheers, Gene
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Peter Wallace
Mesa Electronics
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