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Klipper3d / klipper

Klipper is a 3d-printer firmware
GNU General Public License v3.0
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No fast, smooth moves (look-ahead) without extruder? #2114

Closed ghost closed 4 years ago

ghost commented 5 years ago

I want to build a high-speed CoreXY pen-plotter for an art project, which means I only have X and Y, no extruder. Since I want to go up in speed as far as possible, I need look-ahead for the XY-moves. However the doc says: "Klipper implements look-ahead between moves that have similar extruder flow rates. Other moves are relatively rare and implementing look-ahead between them is unnecessary."

Does this mean that there is no look-ahead without extruder movement? Or does "no-movement" also count as "similar extruder flow rate"?

klipper-gitissuebot commented 5 years ago

Hi @Spacemarine2018,

It did not look like there was a Klipper log file attached to this ticket. The log file has been engineered to answer common questions the Klipper developers have about the software and its environment (software version, hardware type, configuration, event timing, and hundreds of other questions).

Unfortunately, too many people have opened tickets without providing the log. That consumes developer time; time that would be better spent enhancing the software. If this ticket references an event that has occurred while running the software then the Klipper log must be attached to this ticket. Otherwise, this ticket will be automatically closed in a few days.

For information on obtaining the Klipper log file see: https://github.com/KevinOConnor/klipper/blob/master/docs/Contact.md

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KevinOConnor commented 5 years ago

The look-ahead processing is done between moves with no extrusion. (Two moves with no extrusion have "similar (zero) extrusion rates".)

-Kevin

ghost commented 5 years ago

Thanks, that makes it clear!

Can you give any advice on how to make the fastest and smoothest moves? Every sharp corner slows down the movements and introduces vibration, so splitting up a curve into a huge amount of small segments should be ideal when using look-ahead. But what's the limit? When are the segments becoming too small and the look-ahead buffer isn't large enough anymore?

KevinOConnor commented 5 years ago

There is no limit on the look-ahead buffer - it will grow to whatever size is needed to accomplish its goals.

With crazy small segmentation, you might get to the point of overloading the Klipper host cpu (or overloading the software feeding the g-code to Klipper). I don't know where that point is.

I'd guess start with a segment size of 0.100mm - I doubt you'd notice any visual impact at that small size.

-Kevin

ghost commented 5 years ago

Ok, that's great!

How does the smoothed look-ahead come into play? Will the smoothing be triggered earlier or later with segmentation size? Is there any way to influence the threshold when the smoothing will be activated? I want maximum control and predictability of the trajectory, can it be disabled at all?

KevinOConnor commented 5 years ago

It's possible to disable the accel_to_decel mechanism by setting it to a very large value in the config.

As for the other questions - you'd likely need to build the device and then let us know your findings.

-Kevin

KevinOConnor commented 4 years ago

I'm going to close this issue as it looks like the conversation has concluded.

-Kevin