Slow and weird at 140mm/s on curvy/circular path

roboduet

Just finished printing this model: http://www.thingiverse.com/thing:331035/ (small one), using Slic3r 1.2.9, layer height is 0.2 mm.
Got the following results: MaxReps: 5, StepErrors: 0. Underruns: 443

I can provide gcode file or settings used if this can help.

Hugues

Can you send me a Gcode for this one : http://www.thingiverse.com/thing:30420 .There are more curvy path on it and i will compare the gcode with mine…
Thanks,
Hugues

Hugues

I was worried about a mechanical problem so i did a quick test at 200mm/s with a low polygon model :
https://youtu.be/WnnXbRyDGRo

Really happy of it even i didn't finish the print (children never can wait…). The sound is really different from what i encounter with curve. For reference this is a cylinder printed at 70mm/s and i push the speed to 150 % after 10mm. You can see how many blobs are coming...

bot

Are you running a 12v supply? Seems like you're simply commanding too fast of a feedrate. 0.9 degree steppers require double the number of steps as 1.8. CoreXY requires another doubling of steps compared to cartesian. You're losing a lot of speed to resolution that you may not be using in terms of additional accuracy. I'd suggest going back to 1.8 degree steppers, or upping the power supply to 24v (if not already), or both.

Hugues

I'm still in 24v and i will do a test with a 1.8 motor for extruder but i think that's not the problem cause it work well (previous video) when extruding a straight line. And blods seem to come cause extruder is overextruding compare to the motion

dc42

cubexupgrade, I have put an experimental firmware binary at https://dl.dropboxusercontent.com/u/19369680/DuetWiFiServer.bin. You may find that it allows higher speeds before the quality deteriorates. Or not.

bot

It's not the extruder motor per se that needs to be 1.8, it's simply that you are requesting too many steps in too little time. Try the new firmware, see how it works, and then either dial down speed or resolution. These are your only choices really.

deckingman

@DC42. This isn't something that could be cured by changing the value for M566 is it? I don't really understand how it works except that it is most noticeable when printing cylinders. Just a thought….....

dc42

If it's a regular speed up/slow down when printing "cylinders" with small numbers of facets, then higher M566 values do help to achieve higher print speeds. However, the blobbing in the image suggests something else, which is that the cylinder has a very large number of facets (therefore many gcode commands per perimeter). and the gcode processing and lookahead system isn't filling the pipeline as fast as the motion generation system can empty it when it runs at the requested speed. This is confirmed by the high underrun count. The underrun count is incremented every time the lookahead system finds that in trying to achieve the requested speed for one move, it needs to adjust then profile of some earlier move, that move has already been frozen because it is due to be executed soon.

T3P3Tony

In effect, as bot says, the resolution is too high. This used to be a problem with S3D but using Cura or Slic3r did not have the same issues. If you have tried these and still the same issue maybe try reducing the number of facets of the model?

Hugues

Sorry soccer evening (and we won !! ) !
Thanks for your feedback i will try the experimental firmware tomorow, and it's sure exchanging the 0.9 motor by a 1.8 and if not enough going to a direct extruder, the e3d titan combine to 0.9 motor need lot of signal… I design this bot to be speed but this extruder combo were just here cause my own design are still in work in progress (1.8 motor and geared drive 1 : 2).

I experimented this issue with lot of model, astrobot, morena treefrog... Always when curve or and loop are sharp and short.
I tried kisslicer and it seem to work because the oversampling was set really low but i 've the same issue with slic3r on the same cylinder.

Is there a way to calculate the limit the duetwifi can achieve per configuration ?

bot

dc42 has been making improvements in just that area recently, so the numbers are liable to improve. He has mentioned the latest speeds here: https://www.duet3d.com/forum/thread.php?pid=447#p447

I'm not sure that you can directly calculate the exact speeds you can move, as they depend on the number of individual commands that makeup the steps, how many motors are moving, etc.

You could also try lowering the microstepping to 8x instead of 16x, but I'm not sure the results will be excellent.

Hugues

Hi,

So i tested the experimental firmware, i didn't see lot of difference, each time i go upper than 100 mm/s i see and heard this jerky motion and it's not going to the speed asked. I also replace my extruder motor by a 1.8° and the issue is the same.
Is it only me who get this problem when going over 100mm/s in curve ?

I will try your suggestion to lower microstepping and see what's happen. I'm here to test !

dc42

I really don't think lower microstepping will help (just as using a 1.8deg motor didn't), because the problem isn't the step generation rate. Can you tell me the length of each line segment in the gcode for the cylinder that gets jerky above 100mm/sec?

Hugues

I don't know if it can help, this is a cut and past from my gcode file :

; inner perimeter
G1 X100.300 Y114.322 F6000
G1 X99.700 Y114.322 E0.0104 F4650
G1 X99.100 Y114.297 E0.0104
G1 X98.503 Y114.246 E0.0104
G1 X97.907 Y114.171 E0.0105
G1 X97.316 Y114.071 E0.0104
G1 X96.729 Y113.946 E0.0104

Segment are really small…

dc42

So the segments are 0.6mm long. At 100mm/sec that's 167 segments per second. The current firmware tries to freeze moves 1/8 sec before they are needed, so it wants to freeze 20 moves. But the length of the move queue is only 20 moves in firmware 1.14 and earlier, and 30 in 1.15beta1. That explains the underruns.

I've changed the code to freeze at most half of the queue capacity, and increased the queue capacity further to 40 moves. Please try the new beta at https://dl.dropboxusercontent.com/u/19369680/DuetWiFiFirmware.bin. Let me know if it improves the quality at high speed and/or decreases the underrun count.

Hugues

AMAZING ! it's working and now really smooth !
MaxReps: 8, StepErrors: 0. Underruns: 0

I pushed the printer to 140 mm/s and no visual degradation, at 200 it jerk.

Thanks !!!! You're a great master !

bot

Oh sweet.

Just a note, I think it might have worked had he replaced the MOTION steppers with 1.8 degrees, not just the extruder stepper. A firmware fix is always a nicer solution.

Edit: Though, I guess I didn't understand the problem fully. Step generation wasn't the issue, it was merely the lookahead queue? Or was it a combination of both?

elmoret

The problem was lookahead, in other words the g-code segments were very short and the queue was starving.

Changing the steppers or microstepping would not have changed that.

Hugues

The improvement is really, and as my english is not really fluent i took a short moovie, inner path are at 100mm/s in first moovie part and speed increase to 150 % in second part.
https://youtu.be/gBk3flOt3-w

I just notice that when you increase speed by the web the retraction and prime are also afected, mainly the prime, result is a bad seam where speed change because you will appear a big blob.