In order to run betaflight with brushed motor control boards it is necessary to enable the normal PWM generatin mode. The information provided here was tested with version 2.9.1. The actual PWM frequency is configurable. As long as the mosfets switch fast enough use the highest possible value of 32kHz. Values below 20kHz will be audible and distracting.
First, remove all propellers. Then enter the following commands in the cli for 32kHz PWM:
set motor_pwm_rate=32000 #this will set pwm frequency to 32kHz set max_throttle=2000 #brushed boards will use 0-2000 as throttle set min_command=1000 #just to make sure min_cmd is not misconfigured set fast_pwm_protocol=OFF #disable oneshot125 feature motor_stop #motors stopped when not armed #this should be adjusted to your motors: set min_throttle 1060 #the throttle when all motors start to spin save #store settings and reboot!
Now enter the motors tab and test the motors spinning up from 1000 to 2000. The motors should be stopped when set to 1000.