Custom Firmware Inquirie Sphere Drone

Hi everyone. I’ve using released firmwares for multi-rotors e.g quadcopters, hexacopters. But now I want to explore more the dev-world. Specificaly I’m working on a sphere (helium sphere) with 2 propellers and 2 servos. I’ve tested the protoype on arduino working fine. However I’d like to make it work with the pixhawk. The problem is that I don’t know how to begin with. I’ve already downloaded the arduino folder on the github and I know how to compile and upload it. But I don’t know how to proceed on editing the code to my convinience. Any tips?
Best regards. Thanks