I am about to build my own quadcopter from scratch. However i am having problem with understanding how it is possible to control the quadcopter without knowing the current rpm of the BLDC motors. According to my understanding the rpm is needed to calculate thrust force etc. in the mathematical model, which will be used for regulation.
The ESCs I have seen have two wires to connect them to the flight controller. The first one is GND and the second is signal wire, which are used for sending PWM signal- no information about the motor speed. There is also the IMU unit, which provides information about the acceleration of the whole aircraft- but again no information about the motor speed.
I would be grateful if someone could explain it in details how this is.