If the G8302 gimbal is the same as the one from Q500G then those 2 pics may help:
It looks pretty similar to Q500. I have heard that there may be problems with gimbal tilt due to missing initialization (especially valid for CGO2 gimbal).
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If tilt will not work as expected you can try to follow instructions here:
Die CGO2 lässt sich nicht von einem normalen Empfänger ansteuern der ein Signal im Bereich 1000us - 2000us sendet.Hier eine kleine Selbstbaulösung.
www.kopterforum.de
Unfortunately in german but pictures and code are international.
Pin in schematic:
IS = input PWM signal from mainboard
IP = input +5V from mainboard
IG = input ground from mainboard
OS= output PWM signal to CGO2
OP= output +5V (not needed, gimbal supplied with +12V from battery)
OG= output ground