bardiir
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Stuttering travel moves

Mon Sep 11, 2017 6:46 pm

I've first noticed this stuttering on the x axis homing after a print a while ago and haven't given it much thought until now, a print I'm currently at does have a lot of travel moves between the 4 corners and the y-axis this time does stutter every time. The x-axis is smooth. Any idea what could cause this?

https://youtu.be/t0004cR3qfQ

henrik.w
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Re: Stuttering travel moves

Mon Sep 11, 2017 9:16 pm

Hello Bardiir!

Regarding the x-axis; have you traced the path of the belt too see if it rubs against something during it's path through the various pieces? It could be good to see the belt from both sides when the axis is in motion.

Regarding the y-axis; could it be the gcode that contains speed changes during movement to some points - it sounds as that at least, otherwise I do no know what it could be.

/Henrik

bardiir
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Re: Stuttering travel moves

Mon Sep 11, 2017 9:37 pm

X-Axis belt is not rubbing (anymore), also prints are perfect so I can pretty mich exclude any mechanical issues as those would probably cause layer shifts or other issues in the print. Also it's not always on both axis, I only noticed it extremely on the y-axis here and on the x-axis when homing after a print, not when homing from the menu.

As far as I understand gcode there are no speed changes in the movements. So I'm totally lost as of what could cause it :D

bardiir
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Re: Stuttering travel moves

Sun Sep 17, 2017 12:14 pm

Could stuttering occur with the axis binding up? Does the Prusa notice when it comes close to loosing steps while traveling due to increased friction? Because currently I'm facing a cracked x-axis idler part so this might have increased friction over time.


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JeffJordan
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Re: Stuttering travel moves

Sun Sep 17, 2017 1:08 pm

bardiir wrote:
Sun Sep 17, 2017 12:14 pm
...Does the Prusa notice when it comes close to loosing steps while traveling due to increased friction? ....
no, the prusa doesn't "know" where the x-axis really is, it can only calculate it's position by the forward/backward (baby-)steps of the x-motor. there is no hardware to "measure" the position of the extruder carriage during the print (only when homing through the x-/y- endstops).

so if something "interferes" with the movement of the x-motor (slipping pulley, binding bearings, hotend/pinda hitting some upcurling part of the print, cable trunk hitting something .... etc.) you'll get the layer shift we can see at your print.

to reduce issues due to a bad assembly, the selftest (after finnishing the build) does stress the movements of the carriage and the bed with forced high accellerations.... and "looks" afterwards if it could detect the calibration points of the heatbed at the same locations as before.
but during the print, the printer only can calculate the position of the nozzle... which might differ from the real position due to forces that interfere with the moving mechanisms.
dem inscheniör is' nix zu schwör...

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PJR
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Re: Stuttering travel moves

Sun Sep 17, 2017 1:23 pm

Yeah, I get stuttering on travel moves as well, especially when moving to/from the purge tower.

I believe that this is "normal" behaviour on certain prints with a 16MHz microcontroller.

If only a more powerful controller were available, this printer would be superb. The number of steps is just so limited, especially when receiving data and planning the next moves.

Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.

bardiir
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Re: Stuttering travel moves

Fri Oct 13, 2017 6:30 pm

Well at least I'm not the only one suffering. But you're mentioning the 16Mhz of the microcontroller. Actually I've been playing around with the ATMega processors aside from 3D printing a bit in the past and I know that you can overclock them to quite an extend (20Mhz is quitm5e stable, 25Mhz is stable with a passive heat-spreader on the chip). Is the Prusa interrupt controlled so it could take advantage of the higher processing speeds or are there any hard limits in the firmware?

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