Impoved CPAP part cooling flap

The CPAP flap by vitals78 is an amazing printer mod that combines the enormous airflow of CPAP fans with instantaneous control response, allowing for more precise cooling without waiting for the fan to spool up. As a result, both overhang performance and part durability increase significantly, since cooling is turned off and on almost instantly.

However, I find the original design way overcomplicated, with an excessive amount of parts, non-printed transparent panels, small duct diameter, and overall large dimensions.

My remix uses only two printed parts, a motor and several screws. The flap is mounted through a printer panel using four M4 screws. The duct cross-section is increased significantly, reducing airflow resistance with more powerful fans, while being much more compact than the original design. The inlet and outlets are designed for a 19mm ID CPAP tube, standard for non-WS7040 CPAP fans such as the Roborock CPAP in the pictures below. The homing endstop was removed due to sensorless homing being widely available.

This flap will work with any CPAP fan. If you don't have one yet, WS9290 is recommended, since it has the best airflow to noise ratio.

Printer configuration is provided below. Change your pins and driver settings depending on the hardware used (I'm using BTT Kraken). Macros can be used from the original model, just make sure to adjust the homing speed for successful sensorless homing. 
I've set my flap to perform 3 homing attempts in a row, with sensitivity (speed) slightly higher than ideal. This results in 100% reliable homing.

[tmc5160 manual_stepper flap_stepper]
cs_pin: PA10
diag1_pin: ^!PC0
spi_software_sclk_pin: PC6
spi_software_mosi_pin: PC8
spi_software_miso_pin: PC7
driver_SGT: 1
run_current: 0.6
home_current: 1
sense_resistor: 0.075
[manual_stepper flap_stepper]
high_precision_step_compress: True     #Only for Kalico Bleeding Edge
step_pin: PG15
dir_pin: !PB6
enable_pin: !PG14
microsteps: 64
rotation_distance: 1600
velocity: 32000
accel: 1280000
endstop_pin: tmc5160_flap_stepper: virtual_endstop

BOM:

1x Nema 17 stepper motor with standard shaft length

3x M3x8 FHCS

1x M3x8 SHCS

2x M4x4 set screws (same as the ones used in pulleys)

4x M4 SHCS (length depends on your panel thickness)

 

Assembly guide:

1. Mount the motor to the casing using four M3 screws.
2. Press the flap onto the motor shaft until it touches the casing. Ensure that it moves freely without rubbing against anything.
3. Secure the flap on the motor shaft with a M4x4 set screw, inserting it through a hole in the casing. 
4. Plug the hole with a second M4x4 set screw.
5. Drill four holes through your printer panel and attach the flap assembly with four M4 screws, as pictured below.

Do not forget to install an airflow restrictor on your bypass air outlet, as pictured below. The hole in the restrictor should have the same cross section as the cooling nozzles on your toolhead.