Let's suppose I need to work with a three-phase brushless DC motor. The DC motor has only three wires to control its 3 phases, there is no other wires (no Hall effect sensor return for example). Usually one uses a driver (like an ESC) to control the speed of the motor: the MCU sends a PWM signal to the driver which in return controls the 3 phases of the motor.
I know that controlling the duty cycle controls the speed of the motor. But are drivers capable of computing the real-time speed (in rpm) of the motor when the motor does not have feedback wires? If so, how do they do?
Can they compute the real-time torque as well?