Gears animation problem

hello there
i have problem rotating a gear i used a transformation constraint so the first gear rotate twice the other one the problem that when the second gear that use the constraint rotate until 180 degree and backward the rotation
i know i do something wrong i hope someone could help
this is the blend file with video shows the problem
https://mega.nz/#F!mcERiIYI!8LQrqhiOnTzCZeCA46T9JQ