Feature: Fans & Airflow¶

Concept¶

Happy Hare can help heat, cool and exchange the air around your filament. The right fan setup depends on what each fan is there to do: spread heater warmth, cool the electronics, or circulate and exhaust enclosure air. A fan's role is determined by what controls it, not by which fan header it uses. These are MMU fans, separate from the printer's part-cooling fan.

The building blocks¶

A managed fan needs an environment or MCU temperature sensor configured to be offered in menuconfig. A drying cycle requires an environment sensor and heater; a humidity reading enables early completion at a humidity goal. Venting needs a heater, but does not require a heater fan. See Heater & Environment Manager for heater, sensor and vent setup.

Which fan type fits?¶

Example setups¶

These schematic cutaways show a standalone MMU/AFC unit, separate from the printer, with four filament spools. Fans and airflow arrows use orange for heater fans, teal for managed fans, and blue for controller fans. T/H marks a temperature/humidity sensor. Component positions are illustrative.

1. Unheated dry box¶

• Environment sensor: yes, to watch humidity.
• Fans: none needed. Add a managed fan (AUTO, source environment) only if the box can get too warm, for example next to a heated printer chamber.
• Vent: not available without a heater, and you wouldn't want one: opening a desiccant box only lets damp room air in.

2. Heated dryer with a heater fan (the most common design)¶

• Heater: an existing [heater_generic], named in menuconfig (or provided by your board's supplied hardware configuration).
• Heater fan: on the fan that blows across the element. It runs for the whole drying cycle at any drying temperature, and keeps running until the element has cooled.
• Two heater fans on one heater? Enter both pins, separated by a comma. They're driven together.
• Passive heater with no fan? That's fine: leave the heater fan off.

3. Heated dryer with an exhaust vent (e.g. QuattroBox v2)¶

• Heater and heater fan: as in example 2.
• Vent servo: opens the flap every heater_vent_interval minutes while drying.
• Exhaust fan as a managed fan, with fan_forced: 0 (OFF) and heater_vent_run_fan: 1: it's off the rest of the time and runs only while the vent is open.

4. Board inside the heated enclosure¶

• Controller fan on the board fan.
• Turn on "Also run while the enclosure heater is on". During a drying cycle the steppers are usually idle, so without this the board fan stays off while the board sits in a hot box.

5. A separate enclosure per filament (e.g. EMU)¶

• Per-gate configuration: each feature's hardware menu lists its gates. Configure the sensor, fans, heater and vent for each fitted compartment there.
• Circulation fan per gate: EMU's per-gate fans circulate the air in that one filament's enclosure. With no heater involved they're managed fans, one per gate. EMU defaults their AUTO source to the gate's MCU temperature. Control them one gate at a time, e.g. MMU_FAN FAN_FORCED=1 GATE=2.
• Adding heaters (optional): each gate gets its own heater. If a gate's fan is there to spread that heater's warmth, make it the gate's heater fan instead.
• Heater limit: max_concurrent_heaters limits how many gates heat at once, to protect your power supply. Other gates queue.
• Drying selected gates: MMU_HEATER DRY=1 GATES=0,2. With per-gate vents and managed fans, venting operates only on actively heating gates; queued gates wait for a heater slot.

Hardware Setup¶

Examples use the default unit name unit0. Substitute your configured Klipper object name and actual MCU-and-pin names. Configure each fan's voltage and wiring to suit its board and hardware.

All three fan types are under MMU Features / Additions. Heater fans appear in the Heated Chamber group after enabling a heater. Some board profiles supply fixed hardware in a separate configuration file: follow the dimmed hardware-file hint where menuconfig does not offer editable pins.

Managed fan¶

Enable Enable managed fan(s)?, then open Fan h/w config. The enable option is available with Has environment sensors? or Create MCU CPU sensors? enabled.

A shared fan produces this association in mmu_hardware.cfg. The pin below is illustrative; use your board's actual output:

[mmu_unit unit0]
fan             : _unit0_fan

[fan_generic _unit0_fan]
pin             : unit0:PB5
max_power       : 1.0
kick_start_time : 0.5

For a per-gate design, Fan h/w config lists Gate 0 fan, Gate 1 fan, and so on. Each gate has its own pin, power and kick-start settings. Disable entries for gates without that hardware. Blank list positions keep the association aligned with gate numbers:

[mmu_unit unit0]
fans : _unit0_fan0, _unit0_fan1, , _unit0_fan3

See the EMU walkthrough for real per-gate menu examples.

Heater fan¶

Enable Has enclosure heater(s)?, associate the heater under Heater h/w config, then use Configure heater fan(s)? → Heater fan h/w config for a shared enclosure. In a per-gate design, Heater fan h/w config lists each gate's heater fan directly.

Klipper starts a heater fan whenever the heater has a nonzero target, even when drying below Fan heater temp, and keeps it running during cooldown. Happy Hare does not switch it with MMU_FAN or vent control. A passive heater can be configured without a heater fan.

Controller fan¶

Enable Enable controller fan?, then open Controller fan h/w config. It follows this unit's gear and selector steppers. In a per-gate layout, each gate's controller fan follows that gate's gear stepper.

Set the output pin, maximum power, kick-start time, fan speed and idle timeout. Defaults are full speed, maximum power 1.0, a 0.5 second kick start and a 30 second idle timeout after the steppers are disabled.

If the electronics sit inside the heated enclosure, enable Also run while the enclosure heater is on. Per-gate configuration calls this Also run while the gate's heater is on and associates each fan with its own heater. This provides cooling during drying when the motors may be idle. The printer's extruder heater is not used to trigger these generated fans.

Pins and board defaults¶

Any suitable fan output can serve any fan role. Board profiles pre-fill known roles; Spare fan pin(s) in the generated configuration records unused headers for reference, without creating extra fans.

Parameter Setup¶

The Managed fan defaults menu writes these settings to mmu_parameters.cfg:

default_fan_temperature_source : environment  # environment or mcu
default_fan_on_temp            : 49.0         # °C - switch on at or above this
default_fan_off_temp           : 47.0         # °C - switch off at or below this
fan_polling_time               : 5.0          # Seconds between checks
fan_control_enabled            : 1            # 1=enabled, 0=disabled and fans off
fan_forced                     : 2            # 0=OFF, 1=ON, 2=AUTO

default_fan_on_temp must be greater than or equal to default_fan_off_temp. The gap between them is the hysteresis band. Every fan begins with these defaults; per-gate source and threshold changes made with MMU_FAN remain independent until Happy Hare restarts.

The default source is the environment sensor when available, otherwise MCU temperature; EMU selects MCU temperature by default. The modes are:

Heater and controller fan settings live in mmu_hardware.cfg, rather than in the managed fan defaults above.

Commands¶

MMU_FAN                                      # Status for the current unit
MMU_FAN UNIT=unit1                           # Status for another unit
MMU_FAN ENABLE=1                             # Enable automatic management
MMU_FAN ENABLE=0                             # Disable management and turn all unit fans off
MMU_FAN FAN_FORCED=1                         # Force all managed fans on
MMU_FAN FAN_FORCED=0 GATE=2                  # Force gate 2's fan off
MMU_FAN FAN_FORCED=2 GATES=1,2               # Return gates 1 and 2 to AUTO
MMU_FAN SOURCE=mcu GATE=2                    # Use gate 2's MCU temperature
MMU_FAN SOURCE=default GATE=2                # Restore gate 2's configured source
MMU_FAN ON_TEMP=60 OFF_TEMP=58 GATE=2        # Change gate 2's AUTO range

GATE= and GATES= are only valid for a per-gate fan layout. Without either, an action applies to every managed fan on the selected unit. Runtime changes are not written back to the config files, so a restart restores the menuconfig defaults.

Full parameter reference: MMU_FAN.

A bare call reports the controller state, effective AUTO range and each fan's mode, speed, source and current temperature:

MMU_FAN

MMU fan control for unit0: ENABLED
AUTO range in force: OFF <= 47.0°C, ON >= 49.0°C; polling 5.0s
Fan (_unit0_fan): AUTO, 0%, source environment: 31.4°C

MMU_FAN controls managed fans only. Use MMU_HEATER to start a drying cycle; its vent control can temporarily override the managed fan mode.

Printer variables exposed¶

The unit metadata exposes fan or the gate-aligned fans list. See printer.mmu_machine. The underlying Klipper fan objects expose their current speed.

Mainsail / Fluidd¶

Each generated fan type has a Hide in Mainsail / Fluidd option in its hardware menu, enabled by default. Disable it to show that fan in the UI. For a per-gate layout, one switch applies to all gates of that fan type. The hardware screenshots above show the actual option.

Per-gate names append the gate index, for example _unit0_fan2 or unit0_fan2. Visibility changes the generated name, not the control logic. After regenerating and restarting Klipper, update any custom macros that refer to the old object name. Board-supplied custom fan sections may have their own names; follow the indicated hardware file.

Tuning¶

Temperature-driven cooling¶

1. Choose the source that represents what the fan protects: environment temperature for enclosure cooling, MCU temperature for board cooling.
2. Start with ON at 49°C, OFF at 47°C, and a polling interval of several seconds.
3. Check the source temperature and fan mode with MMU_FAN.
4. If the fan cycles too often, lower the OFF threshold to widen the hysteresis band. Keep ON greater than or equal to OFF.

Drying exhaust¶

1. Configure the exhaust as a managed fan, separate from heater airflow.
2. Set fan_forced: 0 and leave heater_vent_run_fan: 1 enabled.
3. Configure and test the drying vent. The fan runs while the vent is open, then returns to its previous mode.

Troubleshooting¶

• No manageable fans on this unit - confirm a fan pin is configured, select the intended UNIT=, and restart Klipper after regenerating the configuration.
• A requested source is unavailable - enable and configure that environment or MCU sensor for the same unit or gate, then restart Klipper.
• A fan never turns on in AUTO - confirm ENABLE=1, return it to AUTO with FAN_FORCED=2, check the reported source temperature, and verify the ON threshold is reachable.
• A fan cycles too often - widen the hysteresis band by lowering the OFF threshold. Keep ON greater than or equal to OFF; inverted values are rejected.

• GATE= or GATES= is rejected - those selectors require a per-gate fan layout. A shared fan always applies to its entire unit.

• A fan stays off when drying at 45 °C - a managed fan on AUTO waits for its ON threshold (49 °C by default). If it serves the heater, configure it as a heater fan.

• An exhaust fan runs throughout drying - change its managed mode to OFF and enable the vent fan override instead of using AUTO.
• A board fan stays off during drying - enable its heater association if it needs to run when the steppers are idle.
• A fan is absent from the UI - check its Hide in Mainsail / Fluidd setting and whether the board provides it through a custom hardware file.
• A pin is used twice - give the output one role; a heater fan cannot also be a managed fan on the same pin.

See also¶

• Heater & Environment Manager - sensors, drying and vents
• EMU - per-gate hardware setup
• Parameters - managed fan defaults
• Mainsail / Fluidd - visibility settings
• MMU_FAN command reference