I connected a sonar to my 3DR quadcopter (with pixhawk on it). I want the quad to keep constant altitude above the ground (about 1.5 meters) during waypoints navigation. Altough the sonar works fine on loiter, it doesnt seem to have an effect when auto-navigating. quick look at the arducopter code made me think that auto mode really doesn't use sonar. does that make any sense? Is there a way to change it?