As a beginner setting up a new quadcopter system, we are struggling to configure a midpoint throttle. We are using qgroundcontrol with PX4. The aircraft flies fine, but the aircraft actively floats up and down although holds GPS position perfectly. Upon trying to land the aircraft, with full throttle stick down, the motors won't return to an idle which hence won't allow us to cut the motors except by using a kill switch when we get close to the ground. If we land the aircraft and let the throttle position return to centre, the quadcopter wants to jump up in the air everytime. Any help would be great.