The load I have is 4.5 cm diameter aluminum plate attached on top of the motor. Yes, I do need a specific rpm. A motor that can spin 0-9000 rpm. According to my understanding of the BLDC theory, since I have 1000kv BLDC motor and wanting the motor to spin at 9000rpm max, therefore I use a 9V adapter, hence at max voltage, the motor should spin at 9000rpm. I used the servo library to move the motor and using the servo value (0-180) degree meaning, 180 is the max speed, hence the rpm is 9000. However, when I key in the value of 160, the motor slow down compared to the 180. So, how much of voltage provided or the voltage drop when in use the 160 speed? Is there any way to measure the voltage drop?