Getting Started with Enraged Rabbit Carrot Feeder (ERCF)¶

The Enraged Rabbit Carrot Feeder (ERCF) is the original Multi Material Unit for Voron printers that started it all. It's evolved considerably since it's formative v1.0 release. This guide walks through the initial menuconfig pass for setting up an ERCF‑style MMU — the screens you’ll encounter, the order they appear in, and the handful of selections that actually matter to getting core ERCF functionality up and running.

As it's evolved (v1, v1.1, v2, v2.5, and v3), the ERCF ecosystem has expanded into a wide range of permutations including:

• Jack Rabbit, servo-less selector variants
• Multiple selector servo options
• Different encoder options (TCRT, and Binky optical encoders)
• Direct‑drive and geared NEMA 14 & 17 options
• Optional entry sensors
• Optional LED's/Neopixel entry / exit / logo bling
• Optional integrated filament buffer

Each revision introduces its own mechanical differences, quality of life improvements and optional features, which means the exact configuration screens you see — and the choices worth pausing on — depend on the hardware you’ve built.

The goal here is simple: get your ERCF‑style MMU installed, recognized by Klipper, and performing base load/unload operations. Once operational, optional capabilities like LED's, entry sensors and more advanced Happy Hare features can be enabled, configured and calibrated.

The examples use the default Klipper object name unit0. You can choose a different name under Name → Klipper object name on the first install, and set a separate Display name for the UI. See Naming an MMU unit; use your chosen name where these examples show unit-specific names or pin prefixes.

Menuconfig Installer¶

First clone the Happy Hare repository as described in Cloning Happy Hare.

Then run the installer:

cd Happy-Hare
./install.sh

The first run opens menuconfig automatically because no .mmu_config exists yet; no -i flag is needed.

This is the installer's default state: MMU Type is Custom Design, the board is unknown, and the CONFIG WARNINGS / ERRORS panel at the bottom lists the choices still needed. As soon as you pick a real MMU type, most of these clear themselves.

Choosing the MMU type¶

Highlight MMU Type and press Enter. Move down to ERCF - Enraged Rabbit Carrot Feeder and press Space to select it. Once selected ((X) ERCF - Enraged Rabbit Carrot Feeder), five new options appear indented underneath — Version,Number of gates/lanes, Selector servo type, Project Options and Design attributes — options that only make sense once Happy Hare knows this is an ERCF. Other settings and options are also enabled based on the MMU design choice.

Confirm the version of your ERCF build. Because ERCF has evolved significantly over time, Happy Hare needs to know which version you built so it can recommend and set appropriate defaults.

Enter the Number of gates/lanes to match your ERCF build. Different ERCF generations use different gate conventions, so lane counts typically fall into multiples of 3 or 4 depending on the generation built (e.g. versions < v2.x, groups of 3, others groups of 4).

The default is 8 gates, but you can change it to match your build — in this case, setting it to 6 gates.

Next, select the Selector servo type. For most ERCF v3 builds the default is the GuoHua A0090, with several other common kit servos included in the list — GDW DS041MG and MG‑90S among them.

You’ll also find the Savox SH‑0255MG, a community‑favorite and widely regarded as the Gucci, ultra‑reliable option thanks to its consistent torque and proven, long‑term durability.

If your build uses a different servo, select Not listed. Servo settings such as min/max pulse widths, etc. are managed using (Top) → Other Settings → Selector servo options later in the menuconfig workflow.

In this example, we have selected the Savox SH-0255MG servo.

Next, review applicable Project Options. If your ERCF build uses the servo-less selector or integrated Enraged Rabbit Cotton Tail (ERCT) Filament Buffer, select and enable these here.

Esc and back out to the top menu, and review the warnings panel again. The hardware warnings have cleared. The remaining warning — "Toolhead type is 'other'" — is exactly what it sounds like: Happy Hare still doesn't know your toolhead, and that's covered in a different getting-started page. Don't worry about it here.

Board type¶

Enter Controller Board type. Because you’ve already told the configurator this is an ERCF and its version, Happy Hare pre‑selects BTT MMB v2.0 with CANbus — the most common controller for more recent ERCF kits and builds. If your ERCF runs a different controller, this is where you’d choose it; default pins for steppers, sensors, and TMC drivers throughout the rest of menuconfig are derived from whatever controller you select here.

MCU connection¶

Esc and back out to the top menu and open MCU connection. ERCF defaults to USB serial, but if your setup uses CANBus, select CAN instead. The installer attempts to auto‑detect USB serial device IDs and CANBus UUIDs where possible for you to choose from. Unfortunately, if Klipper has previously claimed a CANBus device, UUID's can’t be rediscovered easily unless you remove/comment all references from your Klipper/Kalico Happy Hare configuration and power cycle the printer.

If you’re unsure of the USB serial or CANBus UUID's when migrating to v4, you can check your saved mmu.v3/base/mmu_hardware.cfg configuration or klippy.log for previous device ID's/UUID's. The installer will then prompt you for your serial device or CANBus UUID, depending on the option selected. Existing connection selections/mapping's are retained and not overwritten once saved.

The first discovered serial device is selected by default. Press enter to choose a different discovered device.

In this example, we are going to switch to CANBus. Open MCU connection and select CANbus:

A list of discovered CANBus UUIDs is shown. If more than one device is found, select the one that corresponds to your ERCF controller. If only one device is detected, it will be selected automatically. If no UUIDs are discovered, choose Other / manually entered and enter the correct CANBus UUID manually.

Pins: gear and selector direction¶

Esc and back out to the top menu and open Pins / TMC, then Gear pins. GPIO Pin defaults are set based on your MCU controller board and ERCF MMU version selection. Review all pin settings for Gear and Selector steppers to make sure they are correct for your build. Gear direction especially is the one setting that is impossible to set correctly by default or guessing and depends on how the stepper cable is actually wired. You will validate this later when you buzz the steppers to verify their direction in Stepper direction and homing.

This is where you would change the stepper direction if needed.

If the stepper spins the wrong way, you can invert it here without rewiring or hand-editing the configuration. Highlight the Gear dir pin for the stepper and press Enter to open its editor. If that stepper needs reversing, add a ! in front of the pin name — Klipper's standard way of inverting a pin's polarity.

Repeat this for the selector stepper.

Encoder¶

Esc and back out to the top menu and open MMU Features / Additions, then Encoder config.

ERCF requires an encoder to operate (enabled by default) for filament loading and unloading which can also be used for clog detection by the Happy Hare Flowguard facility and automatic calibration of bowden lengths and Rotation Distances. Different ERCF encoder hardware and encoder resolutions are supported depending on your specific build.

Optional ERCF features also can be enabled or disabled here - entry sensors, LED's, and popular community contributed extensions like Sync-feedback buffers (sensors) such as Annex Belay or more recent analog Proportional Sync Feedback sensors, etc. A managed environment fan can use either the MCU CPU temperature or an enabled environment sensor; only enable it when a fan output is actually wired.

The most common choice based on the ERCF version you selected is enabled by default - in this case, for ERCF v3, a Binky 12-vane Encoder. If you have a different encoder configuration open Type to change options. Encoder accuracy is dependent on this configuration and the type and actual number of vanes the installed encoder wheel has.

Select the appropriate type that matches your configuration. 12 (Default) & 8-vane Binky based encoders are the most common. However as the the original reason for reverting to fewer vanes (8 or 10) for direct-drive configurations no longer applies, it's recommended to swap back to 12-vanes for better fidelity and performance.

The TCRT 5000 based encoders are only applicable to original ERCF v1.x builds.

Picking a toolhead¶

From the top menu, select Toolhead. This step is optional — if you skip it, Happy Hare falls back to generic Other/Unknown default dimensions, which is a perfectly fine starting point. But if your toolhead (extruder + hotend combo) appears in the list, selecting it gives you real, community‑contributed measurements instead of generic estimates. Here we’ve chosen A4T WWBMG for A4T Dragon Ace to illustrate.

Esc to backout to the top menu and select Toolhead sensors/settings. This is where you can enable other features such as Toolhead cutter, toolhead and extruder entry sensors if fitted. The community-contributed measurements for Extruder entrance to nozzle and Residual filament, under Toolhead dimensions, can be reviewed and tuned if necessary. For A4T WWBMG for A4T Dragon Ace, the values are88 and 36.5.

Contributions to the toolhead list are always welcome! If you would like to contribute your parameters to this toolhead database, please visit here to add your parameters to future installer updates.

The other two distances Happy Hare can use (Toolhead sensor to nozzle & Extruder sensor to entry) only appear when you have enabled the sensors and remain hidden when disabled.

This is a shortcut, not a substitute: even with community-sourced toolhead measurements, it's useful to learn how to measure and calibrate your own eventually, since small build variations and mods add up. But it's a genuinely good starting point. If your exact combo isn't listed, select Other/Unknown and follow the manual calibration MMU_CALIBRATE_TOOLHEAD process.

Validating Hardware setup & initial calibration¶

The Hardware Validation checklist covers the MCU, selector variants, encoder and the movement/homing model in more detail. The guide below calls out ERCF specific hardware and initial calibration needed.

Selector servo¶

For first time builds and initial hardware setup, start the process with the servo arm removed so you can set the initial angle on the shaft to the default DOWN position before positioning and securing it.

With the servo connected and arm unattached, power up and set the servo to the DOWN position using MMU_SERVO POS=down.

Power down and position the servo arm on the shaft so it sits in the indentation of the top hat in the DOWN position taking care not to move the servo shaft as you do. Secure the arm on the servo shaft and power up so you can validate and adjust servo angles if needed.

1. Disable steppers (MMU_MOTORS_OFF).
2. Set servo to UP position using MMU_SERVO POS=up.
3. Line up the selector with a gate until you can insert a short piece of filament though the gate and into the selector.
4. Issue the following commands to validate the servo angles and expected results:

These are default angles for popular ERCF servos. Note angles differences and just two positions for ERCF v3:

Servo angles can be adjusted dynamically using MMU_SERVO ANGLE=<angle>. To save the angle into the mmu/mmu_vars.cfg persistent state file, issue MMU_SERVO POS=<position> SAVE=1 when you are happy with the angles e.g. MMU_SERVO POS=up SAVE=1.

Stepper direction and homing¶

• Buzz the gear stepper to identify the correct stepper moves (MMU_TEST_BUZZ_MOTOR MOTOR=gear). Power down and swap the stepper cables over or update gear stepper pin settings in menuconfig if the incorrect stepper moves - whichever is easiest.
• Disable the steppers (MMU_MOTORS_OFF) and move the selector away from the homing end stop.
• Buzz the selector stepper to identify it's direction. It should initially move to the right when you issue MMU_TEST_BUZZ_MOTOR MOTOR=selector when looking from the bowden/encoder side of the unit. If it moves to the left, update and invert the selector stepper dir pin in menuconfig (e.g. add or remove the !) in front of the pin.
• Once the steppers are moving in the correct direction, issue MMU_HOME to home ERCF. The selector should move to the homing endstop (on the left) and home the MMU.

Selector calibration¶

Issue MMU_CALIBRATE_SELECTOR AUTO=1 to calibrate the selector and inter-gate spacing. Depending on your build and homing end-stop offset, if the gate spacing isn't CAD perfect or gates tightly butted up against each other, you "may" need to manually calibrate the selector position and offsets for each gate - refer to MMU_CALIBRATE_SELECTOR for details.

Calibration Gear Rotation Distance¶

While Happy Hare sets the default BMG Rotation Distance out-of-the-box, for reliable Encoder operation it's worthwhile manually calibrating the gear stepper Rotation Distance prior to calibrating the Encoder as BMG extruder gear manufacturing tolerances do matter, affecting accuracy. Also as the ERCF uses separate BMG gear-sets for each gate, each gate needs to be calibrated individually.

Once the Rotation Distance for the Gate 0 reference has been set, you "can" optionally enable Autotune rotation distance in (Top) → Other Settings → Calibration/Autotuning to enable Happy Hare to automatically tune rotation distance for each gate when it's loaded.

Calibration: Gear Rotation Distance

Encoder calibration¶

Using gate 0 as the reference, make sure you have 500mm+ of filament ready to go before running MMU_CALIBRATE_ENCODER. Ideally, you are looking for symmetrical + and - counts with a standard deviation as close to 0.0 as possible in both directions. One or two count differences are acceptable. The number of counts will be less depending on the number of vanes your encoder wheel has. Expected counts using an Encoder with a 12-vane wheel:

// Calibrating over 400.0mm...
// + counts: 424
// - counts: 423
// + counts: 424
// - counts: 424
// + counts: 424
// - counts: 422
// Load direction:   mean=424.00 stdev=0.00 min=424 max=424 range=0
// Unload direction: mean=423.00 stdev=1.00 min=422 max=424 range=2
// Before calibration measured length: 400.33mm
// Calculated resolution of the encoder: 0.9445 (currently: 0.9453)
// Encoder calibration has been saved

Checking Basic Operation¶

That's it, you should now be able to load and unload filament using your ERCF MMU. The bowden length will be automatically calibrated the first time you attempt to load filament (autocal_bowden_length: 1 setting) using collision based homing by default, extruder sensors, or compression / proportional sync feedback sensors if defined and set as the extruder homing endstop in menuconfig.

Outside of a print, confirm the basics work end to end (if using ASB/ASA, preheat the extruder to an appropriate temperature as the default minimum preheat temperature is 210°C).

Issue the following commands to validate the basic load/unload operation:

MMU_SELECT GATE=0
MMU_LOAD
MMU_UNLOAD

Each command should complete without error — no pauses, no "not calibrated" warnings you weren't expecting. If something goes wrong here, it's much easier to diagnose now than mid-print; see Operation: Debugging Problems if any of it doesn't behave as expected.

What Next?¶

• Tip Forming and Purge to get your ERCF ready for printing
• Install KlipperScreen (Happy Hare edition) if you want a touchscreen front end, or drive everything from Mainsail / Fluidd — either works, and both are covered.
• From here, explore the rest of this site's Features section one page at a time as you actually need them — Spoolman integration, Toolhead cutter, Blobifier, Shared NFC/RFID reader, EndlessSpool, and the rest. Trying to absorb all of it before your first print is the fastest way to feel overwhelmed by an MMU that, day to day, mostly just works.