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FOCI

Sensorless Homing

FOCI can home an axis by detecting the motion stall from the encoder, so that axis needs no endstop switch. Sensorless homing is optional. Physical endstops keep working, so skip this page if you use them.

Do this after Tuning. The stall detector measures how far the axis lags behind its commanded position, and that lag depends on the tuned gains.

Configure

Section titled “Configure”

Two changes per axis. In [foci <stepper>], set homing_current, the reduced current used while homing:

[foci <stepper>]
run_current: 1.0
encoder_ppr: 1000
homing_current: 0.4

In [<stepper>], point the endstop at FOCI’s virtual endstop:

[<stepper>]
endstop_pin: foci_<stepper>:virtual_endstop
  • homing_current is required on each axis that uses the virtual endstop. Klipper reports a config error if it’s missing. It must be above 0 and at least 0.05 A below run_current.
  • Start at 30 to 50% of run_current.
  • On CoreXY, both motors move for every X or Y home. On the motor whose axis doesn’t use the virtual endstop, homing_current is optional. Without it, that motor homes at full run_current. Set it there too to reduce the current on both motors.

Home

Section titled “Home”

Set homing_speed in [<stepper>] to at least 1.25 × 1000 × rotation_distance ÷ encoder_ppr mm/s, which is 50 mm/s for a rotation_distance of 40 and an encoder_ppr of 1000. Slower than that, FOCI detects the stop later, so the axis presses harder against it before homing completes. Common homing speeds are 80 to 120 mm/s.

Then home:

G28 <axis>

Verify

Section titled “Verify”

Home the axis 10 times. Every home should complete without an error.

Troubleshooting

Section titled “Troubleshooting”
  • Triggers early, mid-travel. Klipper retries once at the second homing speed, then reports an error. Raise homing_current by 0.1 A, raise stall_margin_mm by 0.05, or lower homing_speed, staying above the minimum. stall_margin_mm is how far the axis can lag behind its commanded position, above its normal lag, before it counts as a stall. Keep it below stall_ceiling_mm, the fixed lag limit that always counts as a stall.
  • “No trigger on after full movement”. The toolhead never registered a stall. If it reached the hard stop, lower stall_margin_mm by 0.05. If it stopped short of the hard stop, lower homing_speed.

Change one value at a time, RESTART, and re-run the 10-home check.