45A refers to the continuous working current of the ESC: 45A, if it exceeds this value, it may damage and burn the ESC. 3–6S refers to the voltage range of the power supply, S represents the number of cells. The voltage of each cell is 3.7V, fully charged 4.2V. i.e. 3–6S means that the ESC works in the voltage range of 11.1V–25.2V, beyond which the ESC will be directly burned.