Not functioning gimbal by setting up in Mission Planner

Hello everyone, I almost finished my Xaircraft X650 pro with Pixhawk flightcontroller. The Autotuning went very well and the voltage is very well to. The quadcopter flies very, very good and smooth. (see last topic, thanks everybody for helping me). The last problem I have and I can’t solve it, is setting up the gimbal by Mission Planner I have a Feiyutech gimbal ( I’m very happy with it and works very well), but the only way it works is by connecting it in the receiver (Graupner GR-16 8 channels). In rc-6. The tilt is working in this way. But I want to work it by the Pixhawk. So far as I know, I tried everything. For information: I connect the landing gear in AUX-1, RC-08 (opt.-8) and this works really good. You know, I want to work it by Pixhawk, because I want the camera following me automatically. By the transmitter that’s not working. I googled and looked in YouTube for weeks, noting works. Please has anyone a solvation for me? Thanks in advance.