Hardware connection principle:

expansion board ———- arduino port
Control 1 ——— A0
Control 2 ——— A1
Control 3 ——— A2
Control 4 ——— A3

Servo:-arduino

Servo 1 ——— D11
Servo 2 ——— D10
Servo 3 ——— D9
Servo 4 ——— D6