So when you mean value you mean the input to the controller ? Im using px4 on pixhawk and i believe the output is a signal from -1 to 1 (depending on rotor direction) which then would be the input to the bl-ctrl i suppose.
The normal system is that you use a Mikrokopter FlightCtrl e.g. V2.5
and a MK powerboard with the BL-motor-Ctrls
. Here the FlightCtrl and power board are connected with a 5 pin cable with I2C data interface.
You want to use a different flight ctrl, Pixhawk px4. I do not know the details of this flight ctrl, but I guess it cannot output MK I2C data, so you will use PWM signals to control the BL-motor-ctrls.
Are you using individual BL-motor-ctrls or a power board with 4, 6 or 8 BL-motor-ctrls?
"a signal -1 to 1". Is that a special PWM mode? I believe with a PWM output is normally 0% to 100% speed, not -100% to +100%.
Are you trying to do something with changing motor rotation direction mid-flight? That will not work with BL-motor-ctrl V2.