i need fan help!

[BrianG]

Yup, sounds like you are overworking your 5/6v UBEC. Fans work much like any BL system: they require a certain amount of power to run. So, at lower voltage, they need more current.

If you are using 5v fans, you can put three in series directly on 4s lipo and they will work fine. If you have only two, I would put them in series and use an LM317T adjustable regulator to get 10v. You simply use two resistors to program the regulator to whatever voltage you want. You could use a simple 12v regulator, but that would still be overvolting those 5v fans even in series.

Alternatively, you could another cheaper 5v UBEC to power just the fans. Then use your existing one for the receiver/servo(s).