How is a "x+" layer shift even possible on a delta?

[janjoh]

Hello!

Sooo, to my surprise I woke up this morning and found a "clean" layer shift in X+ direction on my delta printer. I wasn't even aware that this was possible given the kinematics. I thought a delta loosing steps would mean a pretty catastrophic failure.

I found a few articles that adviced to look for missed steps in M122. And I do not appear to have those.

As for currents, I am at 1A with these motors https://www.robotdigg.com/product/1250/0.9-step-angle-NEMA17-stepper-motors
M906 X1000 Y1000 Z1000 E500 I30 ; Set motor currents (mA) and motor idle factor in per cent

Where should I start to look for this, or is this a "once and never again" sort of thing you think? Again, I think I am mainly confused that this would happen in the first place.

M122
=== Diagnostics ===
RepRapFirmware for Duet 2 WiFi/Ethernet version 2.05 running on Duet WiFi 1.02 or later
Board ID: 08DGM-95BLL-N6PSS-6JKD2-3SD6Q-1JTRM
Used output buffers: 1 of 24 (15 max)
=== RTOS ===
Static ram: 25712
Dynamic ram: 93044 of which 0 recycled
Exception stack ram used: 528
Never used ram: 11788
Tasks: NETWORK(ready,628) HEAT(blocked,1232) MAIN(running,3760) IDLE(ready,160)
Owned mutexes:
=== Platform ===
Last reset 11:57:28 ago, cause: power up
Last software reset at 2020-06-08 20:09, reason: User, spinning module GCodes, available RAM 11828 bytes (slot 3)
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x0441f000 BFAR 0xe000ed38 SP 0xffffffff Task 0x4e49414d
Error status: 0
Free file entries: 10
SD card 0 detected, interface speed: 20.0MBytes/sec
SD card longest block write time: 0.0ms, max retries 0
MCU temperature: min 44.8, current 45.0, max 49.0
Supply voltage: min 24.3, current 24.5, max 24.8, under voltage events: 0, over voltage events: 0, power good: yes
Driver 0: standstill, SG min/max not available
Driver 1: standstill, SG min/max not available
Driver 2: standstill, SG min/max not available
Driver 3: standstill, SG min/max not available
Driver 4: standstill, SG min/max not available
Date/time: 2020-06-12 06:21:38
Cache data hit count 4294967295
Slowest loop: 2.12ms; fastest: 0.08ms
I2C nak errors 0, send timeouts 0, receive timeouts 0, finishTimeouts 0, resets 0
=== Move ===
Hiccups: 0, FreeDm: 160, MinFreeDm: 160, MaxWait: 0ms
Bed compensation in use: mesh, comp offset 0.000
=== DDARing ===
Scheduled moves: 3, completed moves: 3, StepErrors: 0, LaErrors: 0, Underruns: 0, 0
=== Heat ===
Bed heaters = 0 -1 -1 -1, chamberHeaters = -1 -1
=== GCodes ===
Segments left: 0
Stack records: 2 allocated, 0 in use
Movement lock held by null
http is idle in state(s) 0
telnet is idle in state(s) 0
file is idle in state(s) 0
serial is idle in state(s) 0
aux is idle in state(s) 0
daemon is idle in state(s) 0
queue is idle in state(s) 0
autopause is idle in state(s) 0
Code queue is empty.
=== Network ===
Slowest loop: 202.17ms; fastest: 0.08ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0) Telnet(0)
HTTP sessions: 1 of 8

• WiFi -
  Network state is running
  WiFi module is connected to access point
  Failed messages: pending 0, notready 0, noresp 1
  WiFi firmware version 1.23
  WiFi MAC address 2c:3a:e8:0a:f1:44
  WiFi Vcc 3.31, reset reason Turned on by main processor
  WiFi flash size 4194304, free heap 24696
  WiFi IP address 172.25.74.150
  WiFi signal strength -57dBm, reconnections 0, sleep mode modem
  Socket states: 0 0 0 0 0 0 0 0
  === Filament sensors ===
  Extruder 0: pos 223.95, errs: frame 0 parity 0 ovrun 0 pol 7 ovdue 0

[dc42]

Surprisingly, skipping steps on one tower of a delta does give symptoms that at first glance look like a layer shift, aligned towards the tower that had the skipped step. If you look more closely, you may notice that the size of the layer shift isn't constant across the whole print.

I expect it's a one-off, so I suggest you retry the print.

[janjoh]

@dc42 said in How is a "x+" layer shift even possible on a delta?:

Surprisingly, skipping steps on one tower of a delta does give symptoms that at first glance look like a layer shift, in the aligned towards the tower that had the skipped step. If you look more closely, you may notice that the size of the layer shift isn't constant across the whole print.

I expect it's a one-off, so I suggest you retry the print.

Yeah, seem to be, and I think I have found the reason. While reprinting i found that these support structures were curling quite a lot during print and my hot end did run in to them at a few occasions.

I wonder if that angle can be made less aggressive without completely disabling Gradual support infill steps.

[Phaedrux]

@janjoh said in How is a "x+" layer shift even possible on a delta?:

I wonder if that angle can be made less aggressive without completely disabling Gradual support infill steps.

You might be able to set a thicker wall for infill to keep it from curling as much or set a fan override for infill.