Steering a 4-engine Crane over APC220

I’m trying to figure out how to drive 4 engines (need to be able to mix them all at same time). with the code below i already figured how to get 2 motors to work.
so probably i’ll get 4 working to by extending the code.
The engines now get their steering from an joystick attached to the same board. the data is read via serial (wireless) back to my mac.

i have some questions:

1: How can i get this to work with 2 joysticks that attached on another arduino and send it over APC220 (from dfrobot) to the other unit.
2: The the code below works but i have a difference is engine-speed (backwards-forward) how can i get this equal.
3: Is there a way to simplify the way to set the engines in ‘0’-state… ( val3 and val4 ) i now have to read the data coming from the pots to set it to zero

hope this makes sence to someone :slight_smile: and can point me in the right direction.

test.pde (3.85 KB)