Tail
One is a pusher and one is a puller, thats what they call it. Check and set your travel distance on your left and right rudder distance and make sure that your end points are not to far out. If the end points are set 100% your servo will be in a bind and causing the servo to be over worked and get hot. I also add a little expo to soften it up some , but I also am not a 3d flyer.