PicoMMU & HappyHare
Thor Sten
Hi guys.
I'm trying to set up Happy Hare with my Pico MMU. I've adjusted the servo angles so that I can no longer push or pull the filament. However, when I run "MMU_CALIBRATE_BOWDEN", the servo moves a bit away (change the angle) and releases the tension on the filament. Which parameter is responsible for this?
Or maybe it's better to not use Happy Hare and just use only Klipper. Because HH got a looot parameters.
Regards, Thorsten
Kurt
Hey Kurt — I’ve seen this exact behavior with PicoMMU on Happy Hare.
What’s happening is normal: when you run MMU_CALIBRATE_BOWDEN, Happy Hare temporarily moves the selector servo to its “move” (or “up”) position, so the selector can travel freely while it measures bowden length. On Type‑A MMUs with a servo selector (like PicoMMU), those named positions are up, down, and move; down grips the filament, while up/move release it. If your move angle releases too much tension, the filament can be pushed/pulled during the routine — exactly what you’re seeing. [github.com], [github.com]
In mmu_parameters.cfg (and, after initial calibration, in mmu_vars.cfg), the relevant items are the servo position angles:
- servo_down_angle → grip/engage filament
- servo_up_angle → release filament
- servo_move_angle → clearance for selector moves (defaults to up if not set)
From HH v2.4 onward, these named angles are stored as calibrated values in mmu_vars.cfg once you run the servo calibration sequence, but conceptually they’re still the same three positions. [github.com]
How to stop it from releasing during MMU_CALIBRATE_BOWDENYou’ve already tuned angles so you can’t push/pull when “gripped”; now make sure the angle Happy Hare uses while “moving” doesn’t let go too far.
Option A (quickest): set servo_move_angle closer to servo_down_angle.
- If servo_move_angle is currently equal to (or very near) servo_up_angle, move it toward the down value just enough that the selector can still travel without rubbing, but the idler stays lightly engaged.
- You can experiment live with:
INI# Console (no restart needed)MMU_TEST_CONFIG servo_move_angle=XXXMMU_SERVO POS=moveIterate until POS=move gives a “light clamp” (can’t hand-push/pull filament), then persist the value in mmu_parameters.cfg (or re-run the servo calibration so it writes into mmu_vars.cfg). [github.com], [github.com]
Option B (recommended if you haven’t run it): re‑calibrate the servo positions properly.
- Run through the Servo calibration step so Happy Hare records good up/down/move angles for your PicoMMU mechanics. Use MMU_SERVO to view/tweak angles, then save. The docs describe using MMU_SERVO to check current angle and the named positions, and explain that down should engage without overshoot and move should clear the arm just enough. [docs.siboor.com], [github.com]
A couple of extra checks (often overlooked)Tip: The wiki notes that move is “ready the servo for selector movement (optional – defaults to up)”. If you don’t need a separate “move” height, you can set servo_move_angle = servo_down_angle (or only a couple degrees above it) so the servo continues gripping during bowden calibration. Just ensure the selector can still traverse freely on your PicoMMU. [github.com]
- State of servo positions in new HH versions – If you upgraded recently, remember v2.4+ stores the calibrated positions in mmu_vars.cfg. Editing only mmu_parameters.cfg might not take effect until you either (a) use MMU_TEST_CONFIG during runtime or (b) re-run the servo calibration to update the stored values. [github.com]
- Run calibrations in order – Happy Hare expects: Selector → Servo → Gear → Encoder (if present) → Bowden → Gates. Re-doing Servo after Gear/Encoder means you should at least re-run Bowden to keep everything consistent. [github.com], [github.com]
The parameter that’s “releasing” your filament during MMU_CALIBRATE_BOWDEN is the servo_move_angle (or its stored calibrated equivalent). Bring servo_move_angle closer to servo_down_angle (or re-calibrate the servo positions so “move” still grips lightly) and the filament will stay clamped during the bowden routine. [github.com]
If you can paste your current MMU_SERVO readout (it prints the current angle and the map for up/down/move) plus the MMU_STATUS line for your PicoMMU, I can suggest a safe servo_move_angle delta to try first.
Bryan Eckert
It’s the “release” angle that Happy Hare uses for the Pico MMU’s servo during certain operations—including MMU_CALIBRATE_BOWDEN. By default, Happy Hare may move the selector to a neutral “between‑lobes” position to release filament tension for safe moves. On Pico MMU builds this can look like the servo backing away and letting the filament slip.
What to change
Set a fixed release angle for the Pico’s servo selector:
- Parameter:
selector_release_angle - Where:
mmu_parameters.cfg(the Happy Hare parameters file) - What to set: Typically
0(or whatever your servo’s “home”/grip-safe angle should be)This option was added specifically for Pico MMU users so that “release” doesn’t pick a mid‑position that reduces tension. [github.com]INI# In mmu_parameters.cfg# Force a specific angle whenever HH wants to "release" the servoselector_release_angle: 0 # -1 = default auto (between lobes); 0 (or your angle) = fixed
Note: Earlier discussion/commits also referred to this as
servo_release_angle; in current configs the user‑facing key isselector_release_anglealongsideselector_gate_anglesand (if used)selector_bypass_angle. [github.com]
Verify your angles
-
Check current servo positions:
MMU_SERVOThis prints the current angle and the named positions. Use it to confirm where “up/down/move” are landing. (General Happy Hare calibration docs show this workflow.) [docs.siboor.com]
-
Show selector angles (handy sanity check):
MMU_CALIBRATE_SELECTOR SHOW=1Newer builds will echo the gate angles and the current release angle. [github.com]
-
Test without restarting (runtime tweak):
MMU_TEST_CONFIG selector_release_angle=0If this behaves as you want, commit it to
mmu_parameters.cfgso it persists across restarts. (Happy Hare supports live parameter edits for testing.) [github.com], [github-wiki-see.page]
Why it happens during MMU_CALIBRATE_BOWDEN
The bowden calibration step automates feeding/retracting and may purposely “release” the selector to avoid scraping or binding while measuring lengths. When “release” is the default “between‑lobes” position, it can unload the filament slightly on a Pico and make it feel like tension was lost. Pinning the release angle to a known safe value (e.g., 0°) prevents that behavior. (See the Type‑A/Pico MMU calibration notes and the step order that includes bowden length.) [github.com], [github.com]
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