The approach taken to find the transfer function of a DC brushless motor was to utilize the step test method. In order gather the required data to generate the plot in the video an encoder needed to be made to measure the time per rotation of the motor.
The sensor used for our encoder was a industry grade Allen Bradley IR sensor. We attached propellers to the motor and placed adhesive reflective tape to the propeller so that the IR sensor see every time the propeller passes.
To gather that data we used an Arduino microcontroller. The Arduino microcontroller was programmed to interrupt each time the IR sensor observed the reflective tape. The interrupt store the Arduino internal clock in microseconds that was then used later to calculate velocity.
The plot with respect to velocity and time can be seen in the video. From that figure using the step test method we can easily calculate the unknown variables (delay time, time constant, K) to find an approximation of the DC brushless motor's transfer function.
