How to interact with landing gear

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Hello,

I work on an hexadrone like typhoon_h480 (that I use on gazebo) and I don't understand how to interact with landing gear, I'm new on ROS (melodic) and sometimes I don't success to translate documentation to node/subscriber/publisher. Im on PX4 with cubeblack pixhawk, but in a first time i'd like see this on gazebo with typhoon h480

I saw this page : https://docs.px4.io/master/en/concept...

How can I translate :

**Control Group #0** (Flight Control)
0: roll (-1..1)
1: pitch (-1..1)
2: yaw (-1..1)
3: throttle (0..1 normal range, -1..1 for variable pitch / thrust reversers)
4: flaps (-1..1)
5: spoilers (-1..1)
6: airbrakes (-1..1)
**7: landing gear (-1..1)**

to : (rospy)

msg = something() msg.param7 = 1 or -1 something.publish(msg)

I hope to be clear Thank you