bldc motor can be converted into a rotary encoder if you have some magnets and a bunch of coils arranged in a circle. Many people use bldc motors as rotary encoders, but they seem to use motors as generators and observe the phases and voltages. In their Hackaday Prize project, they took a different approach: they used bldc motor as coupling inductor, which seemed to be a viable way to convert motors into encoders.
At present, the project aims to send instructions to the microcontroller through serial port and rotate the bldc motor to a specific location. Future work will turn these bldc motors into tactile feedback controllers.
The experimental device of this project is a blue pill microcontroller based on STM32F103. This, combined with a set of half-bridges for driving bldc motor, is really the only thing that requires rotating motors and detecting where the motors are. The circuit uses 6 digital outputs to drive the high side and low side of the half bridge, and 3 analog inputs are used as feedback. The resulting waveforms look like three strange staircases, out of sync with each other, and the correct processing is enough to detect the position of the bldc motor.