Dshot300 Dshot600.
The BB21MCU is called by Dshot series. 48Mhz
Support 2S-6S, 4PWM input, without BEC
Support Oneshot / Multishot / Dshot BLHELI-S firmware
Size 36mm * 36mm (standard 30.5mm mounting hole distance)
Comparison of Dshot with oneshot and multishot:

Dshot is completely digital signal, oneshot and multishot are analog signals. During the use of analog signals, the ESC hardware and software will produce some noise, which is clutter. If there is too much clutter, you need to add a filter capacitor or resistor to filter the hardware at this time. (Off-topic, those who need to disassemble the capacitor probably belong to this situation.) Dshot is a digital signal. In addition to eliminating the need to calibrate the ESC stroke, no filtering is required during transmission! After all, 0 is 0 and 1 is 1, and it will not be deformed or confused; and it is very safe with cyclic redundancy check bit (CRC).

Dshot advantages:
1. It is no longer necessary to calibrate the ESC throttle stroke.
2. Accurate ESC signal is the biggest advantage of digital signal. PWM is an analog signal, which is prone to waveform distortion during transmission.
3. Compared with the current value of "1000 ~ 2000", the Dshot's stroke is from "0 ~ 2048".
4. Above the speed, it is much faster than the oneshot ESC protocol.
5. Security, Dshot comes with four-bit cyclic redundancy check (CRC).

Welding: Weld the capacitors to the positive and negative poles of the power distribution board or ESC respectively. The long legs are positive poles and the short legs are negative poles.