This small and lightweight UBEC features a high efficiency switching mode BEC, providing better heat dissipation when compared to linear voltage regulation. The shielded PCB design and output EMF coil provide a stable, low noise voltage output. The HKU3 also features built-in reverse polarity protection.
You dont need separate UBEC, multiple linear BECs can be connected to KK2.0 (I myself have all 4 on quad without any problem). The Afros have 0.5A linear BECs. Afro connected to M1 will power the KK2.0 and the 2 remaining ESC connected to M2 and M3 will give 1A, which should be sufficient to power the yaw servo on M4. But if you want to go with separate UBEC, for tricopter you will need 2. One for Rx which will then power the KK2.0 and one for M2-M8 to power the servo, because it is separate power circuit. And disconnect the red wires from linear BECs on Afros.
thanks for the quick answer. On most forums it is said that a UBEC is required. Could I power the board with linear BEC of the ESC connected in M1, connect the yaw servo signal wire on KK2 M4, and bring power from the UBEC and - wires directly to the servo?
My recommendations are still the two possibilities I wrote earlier. Your solution might work if you keep the common ground of the M1 ESC and UBEC, but I personally wouldnt separete powering of the servo from the KK2.0. But if you go for it, please write me here how it goes.
This is a very small UBEC. Even the specs say 3A I would use it only for small servos and not more than 4 of them. By the way, it works only up to 5S (6S have more than 23V). For larger models I would use HXT UBEC. I have many of them and none of them ever failed.