Here's another possible solution.
Code:
motor=y-((y-center)/factor)
So for example:
y=168 center=127 and factor=2
148=168 - (( 168 - 127 ) / 2 )
'y' is the joysticj y-axis, center would be you center value for that joystick(normaly 127) and factor could be changed to scale up or down the output speed.