your problem is the code. Whenever you move the joystick you are sending a constant value to the motor/servo/whatever. That constant value is causing the whatever to constantly turn. What you need to do is use the servo set position this takes a value from 0 to 1 from an input and matches it to the servo's position. use this along with some math and the joystick to make it work. Lets say that your servo range (the range of possible/wanted motion) is 90 degrees. You would specify this in the begin vi with servo open. For this to work right you would want is set up like this:
0 degree position(all the way in one direction)=0 servo position=(-1) Joystick position
45 degree position(straight/level)=.5 servo position=0 Joystick Position
90 degree position (all the way the other direction)=1 servo position=1 Joystick position
The degree refrences don't really matter for the sake of the programming they are just there for refrence. What you really need to do is find some math(i have no clue what) to put between the joystick output value and the servo input value that makes 0=-1, .5=0, and 1=1. Once you do this your home free.
See below