[FluidNC Issue#1469] Problem: Unexpected Cross-Axis Movement During Homing on CoreXY Frame

#1 – bdring 于 2025-03-31

Try changing the homing cycles to

– Z: cycle: 1
– X cycle: 2
– Y cycle: 3

…basically change the cycle for Y in your config to 3.

#2 – bibidentuhanoi 于 2025-03-31

Thanks for your reply, but the problem is still there—the toolholder slowly drifts toward the X axis limit switch while homing Y.

$HY
[MSG:Homed:Y]
ok

$HY
[MSG:Homed:Y]
ok

$HX
[MSG:ERR: Ambiguous limit switch touching. Manually clear all switches]
[MSG:INFO: ALARM: Ambiguous Switch]
ALARM:12
ALARM:12
ok

#3 – bdring 于 2025-03-31

Are you sure the microstepping is the same on both motors?

#4 – bibidentuhanoi 于 2025-03-31

I’m using two MKS Servo42 driver boards, both set to 16 microsteps. Sorry for not mentioning that earlier.

#5 – bibidentuhanoi 于 2025-03-31

I forgot to mention that this issue only occurs when I set the kinematics to CoreXY. In midTbot mode, the problem of drifting toward the limit switch disappears. However, with midTbot (using the same steps-per-mm), the Y axis doesn’t move far enough to reach the intended goal distance.

#6 – bdring 于 2025-03-31

That is another clue that suggests a microstepping issue

Try removing the kinematics temporarily and jogging short equal amounts for X and Y. Watch the rotation amount for each motor. Ignore the actual motion of the machine.

#7 – bibidentuhanoi 于 2025-03-31

Based on my measurements and the OLED display on the controller board, each 10mm move results in approximately 90 degrees of motor rotation.

#8 – bdring 于 2025-03-31

without kinematics, do some long jogs at 45 degree angles. that should be straight lines on a corexy machine.

#9 – bibidentuhanoi 于 2025-03-31

Without kinematics, it should be in Cartesian mode, right? In that case, with a long jog (100mm), both axes move when I command a single-axis move.

#10 – bdring 于 2025-03-31

What about a 45 degree angle jog?

#11 – bibidentuhanoi 于 2025-03-31

oh sorry I commanded $J=G91 G21 X60 Y60 F200, and yes, it moves in a straight line along the X axis.

#12 – bdring 于 2025-03-31

I don’t have any more things to try. There are a lot of corexy users and I don’t hear any issues.

A lot of people have given up on those MKS motors. Primarily for reliability issues. They lock up sometimes.

#13 – MitchBradley 于 2025-04-02

You might try adding :low to the step pins in the config file.

#14 – Vorobeyyyyyy 于 2025-04-10

Iam facing same issue for now. Right after touching X endstop i moves X back (as expected) and also Y forward (around 0.5mm). This behavior only when homing – if i move axes manualy they move independent

upd: After some investigation, I think this is because pulloff_mm refers to the motor instead of the axis. Moving the motor back causes both axes to move.

my configuration:

board: None
name: Default (Test Drive no I/O)
stepping:
  engine: RMT (using GPIO)
  idle_ms: 255
  pulse_us: 4
  dirdelayus: 0
  disabledelayus: 0
  segments: 12
uart1:
  txd_pin: gpio.22
  rxd_pin: gpio.23
  baud: 115200
  mode: 8N1
kinematics:
  corexy:
axes:
  sharedstepperdisable_pin: gpio.21
  sharedstepperresetpin: NOPIN
  homing_runs: 2
  x:
    maxratemmpermin: 12000
    accelerationmmper_sec2: 5000
    motor0:
      pulloff_mm: 4
      limitnegpin: gpio.36
      limitpospin: NO_PIN
      limitallpin: NO_PIN
      tmc_2209:
        run_amps: 1.2
        step_pin: gpio.32
        direction_pin: gpio.33
        uart_num: 1
        addr: 0
        use_enable: false
        run_mode: StealthChop
        homing_mode: StealthChop
    homing:
      cycle: 2
      positive_direction: false
      seekmmper_min: 3000
      feedmmper_min: 600
      feed_scaler: 20
      settle_ms: 0
  y:
    maxratemmpermin: 12000
    accelerationmmper_sec2: 5000
    motor0:
      pulloff_mm: 4
      limitnegpin: gpio.39
      limitpospin: NO_PIN
      limitallpin: NO_PIN
      tmc_2209:
        run_amps: 1.2
        step_pin: gpio.25
        direction_pin: gpio.26
        uart_num: 1
        addr: 1
        run_mode: StealthChop
        homing_mode: StealthChop
    homing:
      cycle: 3
      positive_direction: false
      seekmmper_min: 3000
      feedmmper_min: 600
      feed_scaler: 20
      settle_ms: 0
coolant:
  floodpin: NOPIN
  mistpin: NOPIN
  delay_ms: 0
macros: {}
start:
  must_home: false
  deactivate_parking: false
  check_limits: false
arctolerancemm: 0.002
junctiondeviationmm: 0.01
verbose_errors: true
report_inches: false
enableparkingoverride_control: false
uselinenumbers: false
planner_blocks: 16

#15 – Vorobeyyyyyy 于 2025-04-12

Ive created PR to fix this. Iam new in contributing on github so dont know how to link properly
https://github.com/bdring/FluidNC/pull/1478