delta patterning on vertical surfaces

Hi!
I own anycubic kossel plus. This one is originally based on trigorilla board (merged mega+ramps). The only upgrade I made, I've installed 2208 drivers for silent operation. When I print vertical surfaces I often notice geometric patterns on the walls. This patterns are reproducible by printing same g-code again. My assumption is this is because of 8-bit board math vs complex delta kinematic.
My questions to the community are:
1. is my assumption correct (8-bit board math vs complex delta kinematic)
2. has anyone tried to fix it with ARM-based boards (e.g. reARM+ramps)
Thanks in advance!


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Edited 1 time(s). Last edit at 08/30/2019 06:42PM by redscorp.

There are several causes of vertical artefacts on deltas, including the one you mention which is segmentation banding. Another common one is low current microstepping driver issues, but I've not heard of this affecting printers with Trinamic drivers, only with DRV8825 or A4988 drivers. And of course there is ringing, but then the amplitude of the banding fades with distance from the vertical edge.

A number of users have converted their Anycubic Kossel machines to Duet WiFi electronics with RepRapFirmware. Search for Anycubic Kossel at [forum.duet3d.com] for more. Unlike other firmwares, RepRapFirmware doesn't use segmentation to execute motion on linear delta printers. It's also the only firmware with least squares delta auto calibration built in.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

The Duet WiFi board will not do it for me, because I use diamond hotend which need 3 extruders, which means 6 stepper drivers in total.
Can mentioned RepRapFirmware be ran on MEGAs or re-ARM?

Quote
redscorp
The Duet WiFi board will not do it for me, because I use diamond hotend which need 3 extruders, which means 6 stepper drivers in total.
Can mentioned RepRapFirmware be ran on MEGAs or re-ARM?

Both the Duet WiFi and Duet Maestro have expansion boards available. For the Duet WiFi and Duet Ethernet there are the DueX2 and DueX5. For the Maestro there is a 2-driver daughter board.

There is a port of RRF for LPC1768/9 based boards such as re-ARM. But does re-ARM support 6 drivers?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

You have some obvious ringing there which is unrelated to 8-bit electronics. You have way too much elasticity in the printer for the speed/acceleration you are using.

The rest seems to be more like a backslash problem ???

If you think you have problems with poor performance of your 8bit MCU then just lower segments per second to about 80 and print with speed below 100 mm/s. Or even lower segments per second down to about 40 and maximum speed to about 40 mm/s. Then you can expect segmentation errors at most around 5 µm or about one microstep(*) and even 8bit electronics should handle this easily.

(*) Assumes printer dimensions about he same as the original Rostock.

Quote
hercek
You have some obvious ringing there which is unrelated to 8-bit electronics. You have way too much elasticity in the printer for the speed/acceleration you are using.

The rest seems to be more like a backslash problem ???

If you think you have problems with poor performance of your 8bit MCU then just lower segments per second to about 80 and print with speed below 100 mm/s. Or even lower segments per second down to about 40 and maximum speed to about 40 mm/s. Then you can expect segmentation errors at most around 5 µm or about one microstep(*) and even 8bit electronics should handle this easily.

(*) Assumes printer dimensions about he same as the original Rostock.

I\m printing relatively slow. External walls are printing on 30 mm/s. Segments are configured on 100.
I've noticed some wobble in my printing heard this could cause this kind of effects.
If this is not a 8-bit math, can it be stepper/driver precision problem. Will activation of 1/256 steps on 2208-UART solve/reduce this kind of effects?

Thanks in advance!

Quote
dc42

Quote
redscorp
The Duet WiFi board will not do it for me, because I use diamond hotend which need 3 extruders, which means 6 stepper drivers in total.
Can mentioned RepRapFirmware be ran on MEGAs or re-ARM?

Both the Duet WiFi and Duet Maestro have expansion boards available. For the Duet WiFi and Duet Ethernet there are the DueX2 and DueX5. For the Maestro there is a 2-driver daughter board.

There is a port of RRF for LPC1768/9 based boards such as re-ARM. But does re-ARM support 6 drivers?

re-ARM/RAMPS does not support 6 extruders natively but I know how to attach them to them.
Thanks for mentioning expansion boards. They are did not jump on me when I've browsed through their web-site. How do 1/256 steps perform on Duets? Dos it improve print quality?

Axis microstepping greater than x16 doesn't usually improve print quality, but it does make the printer quieter. Some users report that extruder microstepping above x16 can under some conditions slightly improve print quality.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
Axis microstepping greater than x16 doesn't usually improve print quality, but it does make the printer quieter. Some users report that extruder microstepping above x16 can under some conditions slightly improve print quality.

Interesting. Thanks!

Quote
redscorp
External walls are printing on 30 mm/s. Segments are configured on 100

You can go with segments per second down to 40.

Quote
redscorp
I've noticed some wobble in my printing heard this could cause this kind of effects.

Well, it is a kind of backslash. Or behaves similarly.

Quote
redscorp
If this is not a 8-bit math, can it be stepper/driver precision problem. Will activation of 1/256 steps on 2208-UART solve/reduce this kind of effects?

A common cause of imprecise movement at low speeds/accelerations is bad stepper driver / stepper combination. Typically, the problem is slow decay mode of a "dump" stepper driver with high inductance and low resistance stepper. If you suspect this is your problem then:

• changing microstepping will not help; it is unrelated
• switch to fast decay mode (or some more advanced mode doing both fast and slow decay at the same time) will help; this means a bit nosier printer
• adding a ballast resistor or diodes will help; this means more wasted energy

Quote
hercek

Quote
redscorp
If this is not a 8-bit math, can it be stepper/driver precision problem. Will activation of 1/256 steps on 2208-UART solve/reduce this kind of effects?

A common cause of imprecise movement at low speeds/accelerations is bad stepper driver / stepper combination. Typically, the problem is slow decay mode of a "dump" stepper driver with high inductance and low resistance stepper. If you suspect this is your problem then:

• changing microstepping will not help; it is unrelated
• switch to fast decay mode (or some more advanced mode doing both fast and slow decay at the same time) will help; this means a bit nosier printer
• adding a ballast resistor or diodes will help; this means more wasted energy

Do you men something like stepper protector can be useful? I thought they are useless crap.

I can try to switch back to original A4988's to check driver-motor theory, but as I remember people in internet are noticing patterning with A4988's too.

Will fast decay work with TMC2208 and how to enable it? Will it work lauter in this mode?

Edited 1 time(s). Last edit at 09/10/2019 05:54PM by redscorp.

[www.panucatt.com]

These are the ones I'm using, and they default to 'Mixed decay', but just by adding a tiny blob it will switch to Fast Decay.

They're a bit more expensive than the regular Polulus, but they can do 1/128 microstepping and 2.2A, and even has a chip with the heat dissipation pad on top, so it's easy to mount the heatsink correctly. (A lot of drivers use chips with the pad on the bottom, but still place the heat sink on top.)
They're available as both 'regular'(requires power tuning using a screwdriver) or SPI(done digitally on boards that support it)

Other drivers may also have a switching feature. Check their documentation.

@redscorp:
I do not know the "stepper protector" so I do not know whether it can help. If you have a link to the schematic of the "protector" then I can look at it and give you some feedback.

A4988 drivers are in the mixed decay mode by default. The wrong kind of mixed decay where one whole microstepping quadrant is in slow decay. That leads to big position errors when a (low resistance) stepper is driven slowly. See this post to fix A4988 stepper drivers: [reprap.org]
If the post itself is not enough then read the whole thread. There are some links from there for more information.

I do not recall anything about TMC2208. I would need to read the datasheet.

@Gadgetman:
I do not know anything about SD6128. I would need to read the datasheet.
Notice that "mixed decay" often refers to wrong kind of mixed decay where the chip is slow decay in the quadrant when the current is rising and fast decay in the quadrant when current is falling. That is not useful for 3d printers which need precise position at very low speeds. You need more advanced "mixed decay" where most of the PWM period is in slow decay but each PWM period has a fast decay portion as long as the blanking time. DC42 uses such a stepper driver in his duet board which can do this "advanced mixed decay". He may give more feedback what his stepper drivers do.

Looks like I looked at SD6128 in the past and it is probably good: [reprap.org]