Duet Wifi and nimble acceleration issue
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How much PA is needed on a RDD extruder anyway?
Duet WiFi hardware designer and firmware engineer
Please do not ask me for Duet support via PM or email, use the forum
http://www.escher3d.com, https://miscsolutions.wordpress.com -
@dc42 said in Duet Wifi and nimble acceleration issue:
How much PA is needed on a RDD extruder anyway?
That's a good question as the tension of the cable buffers the pressure in the hotend. The problem I had was I was getting zero quality improvements with change of PA and I was getting huge slowdowns so I gave up setting PA on RDD
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@dc42 said in Duet Wifi and nimble acceleration issue:
How much PA is needed on a RDD extruder anyway?
More than I thought, if I use the python script test that has been posted on the forums (and comes up every now and then.) It's the one that prints a double thick wall with motion speeding up and slowing down while printing - and slowly increasing PA over the vertical space.
Based on that test alone, the 30:1 nimble on a smart effector with a standard E3D v6 setup needed a PA between 0.15 and 0.20 PA before the "fast" and "slow" sections started getting near the same thickness. To compare to that, I used to use a titan extruder with a precision piezo orion module and v6 heat break, all hanging from my effector. That only needed a PA of 0.04, and the length between the extruder hob and nozzle was about 15mm longer than what I have with the zesty nimble and smart effector assembly.
What was interesting with the nimble PA test is that the resulting print didn't "tear" at very low levels of PA (as pictures I've seen seem to indicate happens with bowden setups.) In fact, the print looked nearly identical all the way from PA 0 to PA .12 or so.
That leads me to guess that there is some pressure build up in the drive cable causing the issue. Perhaps M572 is entirely the wrong answer to that issue. Unfortunately, PA is the only tool that I know of that deals with that kind of symptom, so it's what I try to use. (If you only have a wrench, but you need to drive in a nail... that wrench starts looking like a hammer.)
I will mention that when I print "normal things" with a higher jerk (250 or so) and a PA of 0.04, as long as I can ignore the noises, the prints do look slightly better than prints with a PA of 0. In particular, it's nearly impossible for me to identify where lines of extrusion start/stop with a PA of 0.04.
All that being said.. I just (about 20 minutes ago) replaced my NEMA17 pancake stepper that was driving the nimble with a 1 amp NEMA14. It has less torque (12.5Ncm vs 16Ncm), but half the rotor inertia, so I'm hoping it behaves better with the sudden direction changes from higher jerk and PA. I think I'd be happier if I could keep jerk at 250 (and not have slowdowns with PA 0.04.)
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I did away with all the settings and interaction problems by going to Portescap P430 258 005 01 3.6 degree ultra low rotor inertia disc permanet magnet steppers for my Nimble extruders. I'll never go back to conventional steppers with a high ratio extruder after using them, they are like a sports car vs a Yugo for starting, stopping, and reversing direction in comparison to the suggested Nema 17 pancake and Nema 14. Expensive new, but they can occasionally be found used at a decent cost.
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@Alexander-Mundy said in Duet Wifi and nimble acceleration issue:
I did away with all the settings and interaction problems by going to Portescap P430 258 005 01 3.6 degree ultra low rotor inertia disc permanet magnet steppers for my Nimble extruders. I'll never go back to conventional steppers with a high ratio extruder after using them, they are like a sports car vs a Yugo for starting, stopping, and reversing direction in comparison to the suggested Nema 17 pancake and Nema 14. Expensive new, but they can occasionally be found used at a decent cost.
Where did you get yours? I cannot (so far) find a vendor in the US.
Thanks.
Frederick
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Used on ebay
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@Alexander-Mundy said in Duet Wifi and nimble acceleration issue:
Used on ebay
It seems that there are currently none there.
Too bad, I would like to try one.
Frederick
Printers: A FT-5 with the 713 upgrade bits, a custom MarkForged style, a small Utilmaker style, a small CoreXY from kit and a E3D MS/TC setup. Various hotends. Using Duets (2 and 3) running 3.4.6
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Just wanted to thank you all very much for input and sharing, don't want to be ungrateful. I had some success with 120 E acceleration and 0.03 PA. On a side not my prints look a little different since moving from direct to nimble, walls have weird "pattern". I need to test more to eliminate speed factor. Also ill be looking to get that portescap stepper it seems to be a way to go. Again Thank You!
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@svalsorim said in Duet Wifi and nimble acceleration issue:
On a side not my prints look a little different since moving from direct to nimble, walls have weird "pattern". I need to test more to eliminate speed factor.
The patterns are command and a known issue in V2 extruders. They are apparently caused by 2nd order resonance in the helical gears. (Us old farts would remember the diff howl typical in pre 70's cars)
You'll need to go to the discord channel and register to have the gears replaced when a fix is available.
My experience was that no amount of tuning would get rid of it completely.
Also be aware that the breech will soften if exposed to much heat. They advertise 60 degrees.
In my case, printing ABS generated enough ambient heat (unheated enclosure) to make the breech soften and cause under extrusion.
I like the design philosophy, so when they can sort the gears I might get it out of the draw again, but I was unable to realize the benefits that the design promised.
And I'd have to make a breech to work reliably at ABS temps.
Others seem to love them, so perhaps it comes down to the sum of the manufacturing tolerances in the particular unit you get. -
@OwenD said in Duet Wifi and nimble acceleration issue:
They are apparently caused by 2nd order resonance in the helical gears.
Why wouldn't a speed change allow avoiding the resonance?
Thanks.
Frederick
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@fcwilt 4 times what I paid but still way cheaper than retail:
https://www.ebay.com/itm/192599739125
If you look at the pics it is the same part#. In fact mine came with the "theta assembly" label pigtail also. Escap is Portescap's old name.
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The patterns were also a sometimes symptom with V1. Mine were some of the first sold and 1 printed flawless and 1 had the repeating pattern. Turned out to be the shaft undersized on the hob which Zesty replaced. Some of the original flex shafts had a defect and Zesty sent everyone new replacements. Same with the bodies. I give them kudos for customer service. Later 1 of them started the patterns and it was a worm bearing going bad. I replaced all bearings with ceramic ones and no problems since. I certainly wish I would have bought additional V1's while they were available. Too bad they have had the technical problems, when working properly (and IMO with the portscap stepper no need to go to V2 with 20:1 as I have tested retraction all the way up to 100 mm/s without skipping) they are top notch.
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@Alexander-Mundy said in Duet Wifi and nimble acceleration issue:
@fcwilt 4 times what I paid but still way cheaper than retail:
https://www.ebay.com/itm/192599739125
If you look at the pics it is the same part#. In fact mine came with the "theta assembly" label pigtail also. Escap is Portescap's old name.
Thanks much.
Frederick
