Hans you need to use the dedicated channel 1-4 channels are proportional yes? meaning they can travel the same as the sticks are moved and let me repeat my self with a standard servo you do not have positive locking, as far as I know without battery drain.
positive lock means that when the servo is finished moving it is in a locked position so the gear doesn't fold on landing standard servos do not have this feature so user beware.
coming for a landing and having your gear fold on you sucks and can damage or destroy a plane pretty quick.