During extended periods of synchronised printing without intervening tool changes, alignment between extruder and gear steppers can gradually drift. Even with precise calibration, factors such as under extrusion during purging, printing at high speed near upper flow limits, friction and drag and the inertia of heavy spools can conspire to cause slippage in either the extruder or more commonly—the downstream gear stepper. Over time, this mismatch accumulates and can lead to print artefacts caused by missed steps or suboptimal extrusion rates. Although not always apparent on well-tuned systems, it's a legitimate and demonstrable issue.
Proportional sync-feedback sensors address this using linear Hall Effect sensors (or similar), providing analog positional telemetry to Happy Hare allowing it to continuously adjust and fine tune gear stepper Rotational Distance (RD).
This redesign is based around the PSF v1.0/1.1 or later proportional sensor kit from Kashine6 on ALiexpress and is intended to be used with the Happy Hare MMU ecosystem and new Flowguard / Sync-feedback controller.
This design is based on the original works of Tshine's Dual Micro-switch based Sync-feedback Sensor and subsequent adaption to accomodate Proportional Sync-Feedback (PSF) sensor circuitry and magnet by Kashine6. Its been optimised (sensor / magnet placement, mainbody changes, etc) and significantly shortened (65mm - 6.2mm shorter than Kashine6's version) to work better with top mounted MMU's and bowden entry ports.
Note
Step files (rather than STLs) are included for printing the sensor with Multi-colour tick marks or Single-colour with recessed tick marks. Depending on MMU / Printer orientation, you may elect to invert all the parts (mirror along x axis in your slicer) to move the connector to the top to streamline wiring.
Assembly is reasonably straight forward.
- Install ECAS fittings without rubber boots
- Install D4 x 15mm magnet in PSF shuttle until it's flush with the end of the shuttle (magnetic orientation doesn't matter)
- Straighten the PTFE tube you will be inserting into the "Stumpy" PSF body
- Insert the PTFE tube from the right, threading through the spring and PSF shuttle until it bottoms out on the recess of the body. Install the ECAS clip to secure
- Hold the shuttle up against the stop on the left hand side of the body. Using a small screw driver or hex key, push and adjust the magnet until it bottoms out in the recess for it on the body. Once in position, it should sit proud of the PSF shuttle by 4mm as per the image below
- Use 2 M2 x 6mm SHCS screws to install the PSF module
- Use a M2 x 6mm SHCS screw to secure the cover
- Verify the shuttle moves freely across its full range of movement
| Item | Specification | Quantity |
|---|---|---|
| PSF v1.1+ Board | Kit from Aliexpress includes all the required parts below | 1 |
| Spring | 0.4 mm × 6 mm × 20 mm, spring steel (cut down and shorten kit spring if too long | 1 |
| Magnet | D4 mm × 15 mm N35 | 1 |
| ECAS04 Bowden connector & clips | 2 | |
| M2×6 mm SHCS screw | 3 |
This needs to be used with Happy Hare Flowguard and integrated support for Proportional Feedback Sensors.
Please refer to https://github.com/moggieuk/Happy-Hare/wiki/Synchronized-Gear-Extruder2 for detailed setup and configuration instructions.
Note
You will need to switch to the Happy Hare FLOWGUARD branch before configuring the sensor until the beta is complete and merged with the main Happy Hare release.
cd ~/Happy-Hare
./install.sh -b FLOWGUARD
MMU_PARAMETERS.CFG
The "Stumpy" PSF Sync-Feedback Sensor has 14mm of movement.
sync_feedback_buffer_range: 14 # Travel in "buffer" between compression/tension or one sensor and end (see above)
sync_feedback_buffer_maxrange: 14 # Absolute maximum end-to-end travel (mm) provided by buffer (see above)Use MMU_CALIBRATE_PSENSOR to determine the min and max ADC raw values returned by the sensor to set the following parameters in MMU_HARDWARE.CFG. Your sensor may return different values than the example below e.g.:
sync_feedback_analog_pin: mmu:<ADC GPIO> # The ADC pin where the proportional filament pressure sensor is installed
sync_feedback_analog_max_compression: 0.0038 # Raw sensor reading at max filament compression (buffer squeezed)
sync_feedback_analog_max_tension: 0.9919 # Raw sensor reading at max filament tension (buffer expanded)
sync_feedback_analog_neutral_point: 0.4979 # Neutral pointNormal orientation (as designed)
[Optional] Inverted (Mirror all parts along x axis in your slicer)
