I want to build an underwater quadcopter. The difference here is that the motors are mounted up-side-down and have model boat propellors. Obviously RC is not possible underwater, so a cable goes down to the quadcopter and an Arduino microcontroller will talk to the flight controller. I understand the input on the flight controller receives standard servo signals from a radio receiver normally. I need to be able to emulate the signals put out by the receiver. 

Can anyone point me in the right direction? While the signals coming from the radio receiver are standard servo signals, there is also some kind of startup sequence that I don't understand. This evidently has something to do with "arming" the ESCs.

Would appreciate any help here. 

Thanks, Theron Wierenga

Not sure about how the signal propagates through water, but...