This feature requires the BDsensor firmware version(you can sending M102 S-1 to get that version,not the hardware version on the sensor) is V1.1b or > V1.2b or purchased after March 2024 , else you need to flash the firmware into BDsensor with external hardware tool like STlink.
How is it triggered?
If the nozzle or bed is stopped by the collision, the distance data measured by bd sensor will also be stop changing, then the bd sensor will output a stop signal quickly.
What’s the process?
It can be triggered after the nozzle touch the bed while homing—>then move slowly up until the nozzle just leave the bed—>setting this position as the 0 position of z axis.
Auto z_offset calibration.
meanwhile you still can manually adjust the z_offset for different fialment.
Overcome the temperature drift.
The temperature drift will change the z_offset, but it does not change the range of bed_mesh heightmap with BDsensor. that means the bed mesh is the same even with different temperature.
collision_homing, collision_calibrate into section [BDsensor] and recommend to set the z_offset:0 at first, You can adjust this later.[BDsensor]
...
collision_homing:0 # set it 1 to enable homing with nozzle collision sensing. disable it by setting 0.
collision_calibrate:0 # set it 1 to enable auto calibrate BDsensor with nozzle collision sensing. disable it by setting 0.
# that means we do not need to manual move the nozzle on the bed and do paper test before sending calibrate command M102 S-6.
z_offset:0
...
The sensitivity depends on the speed, the slower speed the higher sensitivity, so you need to adjust the speed of Z axis, the homing_speed and second_homing_speed should be in the range of 2 ~ 5.
If there is warning message while homing like this “warning: triggered in air,812” you can try to the increase second_homing_speed a little in the section [stepper_z], for example from 3 to 4
for example.
[stepper_z]
....
endstop_pin: probe:z_virtual_endstop
#position_endstop: 0.0
position_max: 250
homing_speed: 5
second_homing_speed:3
homing_retract_dist:5
homing_retract_speed:2
z_hop and homing_retract_dist should be >=5[safe_z_home]
z_hop: 5
[stepper_z]
homing_retract_dist:5
[BDsensor]
...
speed:3 # this speed only works for the z tilt and PROBE_ACCURACY command.
...
Use
zero_reference_position
[bed_mesh]
horizontal_move_z:1 # 0.7~1.0mm is recommended
zero_reference_position: 150, 160 # Set this value to be the same as home_xy_position that is in the section safe_z_home
....
The nozzle should be cleared or heated up to soft the filament residues. but Don’t heat up the nozzle too high while homing with soft PEI like Whambam that maybe leave a hole on that PEI with high temperature.
Please don’t set the speed too high or too slow. if the speed is too high that maybe damage your hotend or bed, or too slow that may be triggered in the air.
Please send G28 Z about 10 times, and then see if the output data on the console are stable after each G28 Z .
https://www.pandapi3d.com/post/nozzle-collision-sensing-with-bdsensor
Video: How to start contact probe