On 9/27/26 16:41, Chris Albertson wrote:
I like the way Klipper solved the communications jitter issue. Klipper is a
lot like LCNC. There is a central Linux computer that reads the G-code file,
does planning and the math, and then the low-level stuff like generating
wavforms to drive a stepper motor or whatever is some on microcontrollers that
can be truely “hard” real time.
What Klipper does is simple. The microcontroller clocks are synchronized to
the Linux system. Then the Linux host attaches a “target time” with each
movement command. The microcontroller then buffers the command until the exact
right time. This way, millisecond-level RT jitter in Linux does not show up
on the motors.
Something I have noted with my 3d printers. A near total lack of
millisecond stalls in those I have re-motored with closed loop motors on
shockingly high voltages, like 72 although the controllers are rated for
90 to 110 volts. But didn't have what it takes to investigate. Thank
you Chris.
What I have found is that these same drivers, use a FAST opto in the
step/dir circuitry, and that this FAST opto has a max of 15 milli-amps
which the BTT cards, using a full 5 volt rail to rail swing, can put
nearly 50 ma into the opto's when wired direct, eventually blowing
them. And its too crowded to get at it to replace the 6n137's with the
soldering gear I have, so have to replace the whole nearly $50 driver.
So put a 150 ohm in series with the step & dir sigs.
With regard to LinuxCNC, I suspect this will need a major rewrite as it
will likely touch quite a bit of heart of LinuxCNC. But it sure sounds
like a worthwhile effort, an effort I hope to see if I live that long.
I'll be 92 in a few days. So 2.10 or 2.11 are bug fixings, then fork it,
let us run on it, and hit us with 3.0 incorporating this in a couple
years when most of the inevitable bugs have been dealt with. At the same
time, you might consider one (or more) of the BTT controller cards for
the actual I/O. They sure can make and old printer march to a new tune.
The Octopus Pro V1.1 boards can drive 8 motors etc for $65.
Cheers, Gene
This way, one can get 10-microsecond-level timing without real-time Linux.
On Sep 27, 2026, at 11:24 AM, Nicklas SB Karlsson <[email protected]> wrote:
Now it seems to work reliable with jitter far below 1 millisecond.
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