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calibration
This page records the SPD-to-RPM and SPD-to-flow calibration measured on the CCL-ALTAR-01 unit specifically. If you replace the StoneFlower controller, change firmware, or swap the auger/ram ratio away from 1, this data is no longer valid — re-measure.
📷 Photo of the calibration test rig: graduated cylinder under nozzle, timer, ram-position marker.
| Quantity | Equation | Domain |
|---|---|---|
| Auger RPM | RPM = 0.386 · SPD + 14.94 |
SPD ≥ 50 |
| Volumetric flow | Flow [mL/min] = 0.097 · SPD + 3.75 |
SPD ≥ 50 |
Per-revolution displacement: the BIG ram delivers 0.2513 mL per ram revolution.
Dead zone: SPD 0 to ~40 → 0 RPM. This is why S1 is the convention for "extruder off" in generated G-code — anywhere in the dead zone is true zero flow, but S1 is the smallest valid command and so is the canonical idle.
Sweet spot: the StoneFlower manual recommends 1–3 rev/s for paste-clay extrusion. With the CCL curve, that maps to:
1 rev/s = 60 RPM → SPD ≈ 117
3 rev/s = 180 RPM → SPD ≈ 428
So the working SPD range for normal printing is roughly 120–430.
Re-measure the curve if any of these change:
- Auger / ram ratio pot moved off
1 - Microstepping pot (A6) repositioned
- Speed pot (A7) repositioned
- StoneFlower firmware reflashed
- Stepper or driver swapped
- Significant ram seal or auger-flute wear
- Park the robot off the build plate; clamp a graduated cylinder under the nozzle.
- With the cell at idle, command discrete SPD values from a script: 50, 100, 200, 300, 400, 600, 800.
- Hold each for a fixed dwell (e.g. 30 s); record RPM (visible from auger marker if accessible) and volume captured.
- Fit linear regression separately for RPM(SPD) and Flow(SPD) over the non-dead-zone range.
- Update the equations on this page with the new fit and date the change.
📷 Plot of the SPD→RPM and SPD→Flow regressions with measured data points.
⚠ Don't extrapolate. The linear fit is only validated in the measured domain. Below the dead zone, treat as zero flow; above the manufacturer-recommended max, the auger physics gets non-linear.
The front panel has positions 0.25, 0.5, 1, 2, 4 for the auger/ram ratio. Only 1 has been characterized. Other positions are valid hardware settings but the SPD→flow relationship will scale (approximately, not exactly) with the ratio. If you experiment with another position, log it in Lab studies and re-fit on this page.
See also: Materials for the water-percent / clay-recipe side of extrusion behavior, and G-code conventions for the S1 idle rule.