# Filament\_motion\_sensor not working with extruder\_stepper **URL:** \ **Category:** General Discussion\ **Created:** [September 2, 2025, 10:32pm UTC](https://klipper.discourse.group/t/filament-motion-sensor-not-working-with-extruder-stepper/24742 "2025-09-02T22:32:45Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![joshua70448](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/joshua70448/32/20411_2.png) [@joshua70448](https://klipper.discourse.group/u/joshua70448)\ **Post date:** [September 2, 2025, 10:32pm UTC](https://klipper.discourse.group/t/filament-motion-sensor-not-working-with-extruder-stepper/24742/1 "2025-09-02T22:32:45Z")
### Basic Information: Printer Model: Modded Ender 3 v2 MCU / Printerboard: Octopus v1.1 Host / SBC: Raspberry PI 4B klippy.log [klippy.log](https://klipper.discourse.group/uploads/short-url/iX3JuuUTK3eMG6rGXrb7PvmxrmA.log) (3.5 MB) ### Describe your issue: I’ve got 4 extruders connected to a single hotend. The first extruder is defined as an `extruder` object, and the others are defined as `extruder_stepper` objects. I’ve got some BTT smart filament sensors (v2) that I’d like to add to each extruder. The first one works fine, but when I try to add the second one I get this error: `Internal error during ready callback: 'PrinterExtruderStepper' object has no attribute 'find_past_position'` I saw a [similar post from last May](https://klipper.discourse.group/t/filament-motion-sensor-on-2-in-1-out-hotend/16617/5) with a solution involving adding the missing `find_past_position` method to the `PrinterExtruderStepper` class. The author said they might submit a PR to add this fix to the code base, but it doesn’t look like this was done. Is there a better way to configure filament motion sensors on `extruder_stepper` objects? Should the fix suggested in that post get committed and merged? Thanks in advance! ---
**Author:** ![nefelim4ag](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/nefelim4ag/32/2387_2.png) [@nefelim4ag](https://klipper.discourse.group/u/nefelim4ag)\ **Post date:** [September 3, 2025, 12:43am UTC](https://klipper.discourse.group/t/filament-motion-sensor-not-working-with-extruder-stepper/24742/2 "2025-09-03T00:43:23Z")
Unfortunately, the log file is missing the Klipper version and seems modified. Regardless, the method exists in the mainline. So, you probably have to update to a more recent release than the one you have. ```auto d77928b17b klippy/kinematics/extruder.py (Kevin O'Connor 2021-02-22 21:38:33 -0500 257) def find_past_position(self, print_time): 6627d036ac klippy/kinematics/extruder.py (Kevin O'Connor 2022-02-21 13:51:27 -0500 258) if self.extruder_stepper is None: 6627d036ac klippy/kinematics/extruder.py (Kevin O'Connor 2022-02-21 13:51:27 -0500 259) return 0. ffbd2698fe klippy/kinematics/extruder.py (Kevin O'Connor 2022-01-11 14:21:57 -0500 260) return self.extruder_stepper.find_past_position(print_time) ``` Hope that helps. * * * Ah, well, you probably right. But it is strange, you do request the extruder, not the `extruder_stepper` Hmmm. * * * Aaah, there is more then one filament\_motion\_sensor ---
**Author:** ![joshua70448](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/joshua70448/32/20411_2.png) [@joshua70448](https://klipper.discourse.group/u/joshua70448)\ **Post date:** [September 3, 2025, 1:02am UTC](https://klipper.discourse.group/t/filament-motion-sensor-not-working-with-extruder-stepper/24742/3 "2025-09-03T01:02:37Z")
Ah sorry, I was trying to focus the log on the error itself, here’s the unmodified log. As for the release being outdated, I’m on v0.12.0-159 which is admittedly a bit old, but the problem seems to be with the `PrinterExtruderStepper` class used by `extruder_stepper` (as opposed to the `ExtruderStepper` class you’ve referenced, which my first extruder uses without any issues). The [source for the PrinterExtruderStepper class](https://github.com/Klipper3d/klipper/blob/master/klippy/extras/extruder_stepper.py) hasn’t been updated in 3 years so I’m wary of updating unless I know it’ll fix the problem. [klippy.log](https://klipper.discourse.group/uploads/short-url/iX3JuuUTK3eMG6rGXrb7PvmxrmA.log) (3.5 MB) ---
**Author:** ![joshua70448](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/joshua70448/32/20411_2.png) [@joshua70448](https://klipper.discourse.group/u/joshua70448)\ **Post date:** [September 3, 2025, 1:04am UTC](https://klipper.discourse.group/t/filament-motion-sensor-not-working-with-extruder-stepper/24742/4 "2025-09-03T01:04:48Z")
> [@nefelim4ag](#): > > Aaah, there is more then one filament\_motion\_sensor Haha yeah, the first `filament_motion_sensor` works like a charm, it’s the additional sensors that aren’t playing nicely. ---
**Author:** ![joshua70448](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/joshua70448/32/20411_2.png) [@joshua70448](https://klipper.discourse.group/u/joshua70448)\ **Post date:** [September 3, 2025, 1:09am UTC](https://klipper.discourse.group/t/filament-motion-sensor-not-working-with-extruder-stepper/24742/5 "2025-09-03T01:09:38Z")
Here’s the pertinent config, if it helps any: ```auto # Extruder 0 # Driver = DRIVER4 / MOTOR4 # Heater = HE0 # Thermistor = T0 # Runout = DIAG4 [extruder] max_extrude_only_distance: 450 max_extrude_cross_section: 2 step_pin: PF9 dir_pin: PF10 enable_pin: !PG2 microsteps: 16 rotation_distance: 22.725 # 22.748 nozzle_diameter: 0.800 filament_diameter: 1.750 heater_pin: PA2 sensor_pin: PF4 sensor_type: EPCOS 100K B57560G104F #control: pid # tuned for stock hardware with 200 degree Celsius target #pid_Kp: 28.22 #pid_Ki: 3.12 #pid_Kd: 63.77 min_temp: 0 max_temp: 240 # PLA 0.4mm nozzle = 0.6944 #pressure_advance: 0.6944 [tmc2209 extruder] uart_pin: PF2 run_current: 0.800 stealthchop_threshold: 999999 [filament_switch_sensor runout_switch] switch_pin: PG11 [filament_motion_sensor runout_encoder] switch_pin: PG10 detection_length: 4 extruder: extruder # Extruder 1 # Driver = DRIVER5 / MOTOR5 # Runout = DIAG5 [extruder_stepper extruder1] extruder: # If blank, not synchronized step_pin: PC13 dir_pin: PF0 enable_pin: !PF1 rotation_distance: 22.725 # 22.748 microsteps: 16 [tmc2209 extruder_stepper extruder1] uart_pin: PE4 run_current: 0.800 stealthchop_threshold: 999999 [filament_switch_sensor runout_switch1] switch_pin: PF6 [filament_motion_sensor runout_encoder1] switch_pin: PF5 detection_length: 4 extruder: extruder_stepper extruder1 ``` `extruder` is the first extruder motor, which is tied to `runout_switch` and `runout_encoder` and works without any problems. `extruder1` is the second extruder motor, which is tied to `runout_switch1` and `runout_encoder1`. The switch sensor is fine, but the motion sensor throws the error. If I use `extruder: extruder1` then it complains that the config object doesn’t exist. ---
**Author:** ![nefelim4ag](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/nefelim4ag/32/2387_2.png) [@nefelim4ag](https://klipper.discourse.group/u/nefelim4ag)\ **Post date:** [September 3, 2025, 1:25am UTC](https://klipper.discourse.group/t/filament-motion-sensor-not-working-with-extruder-stepper/24742/6 "2025-09-03T01:25:20Z")
Yes, I can reproduce that locally, I look for what can be done. This seems correct: ```auto diff --git a/klippy/extras/extruder_stepper.py b/klippy/extras/extruder_stepper.py index 4ac5289f8..79d4feef8 100644 --- a/klippy/extras/extruder_stepper.py +++ b/klippy/extras/extruder_stepper.py @@ -15,6 +15,10 @@ class PrinterExtruderStepper: self.handle_connect) def handle_connect(self): self.extruder_stepper.sync_to_extruder(self.extruder_name) + def find_past_position(self, print_time): + return self.extruder_stepper.find_past_position(print_time) + def sync_to_extruder(self, extruder_name): + return self.extruder_stepper.sync_to_extruder(extruder_name) def get_status(self, eventtime): return self.extruder_stepper.get_status(eventtime) ``` ~~I will make an PR~~ : [extruder\_stepper: define missing public methods methods by nefelim4ag · Pull Request #7032 · Klipper3d/klipper · GitHub](https://github.com/Klipper3d/klipper/pull/7032) Thanks for the report. ---
**Author:** ![system](https://global.discourse-cdn.com/free1/uploads/klipper/original/1X/64419bf2aac6639e6ef5cef200dcd456b0a01ac3.png) [@system](https://klipper.discourse.group/u/system)\ **Post date:** [October 3, 2025, 11:25am UTC](https://klipper.discourse.group/t/filament-motion-sensor-not-working-with-extruder-stepper/24742/7 "2025-10-03T11:25:37Z")
Closed on October 3, 2025, 11:25am UTC This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.