question about a logic circuit!!!!!

hi i want to built a robot with 2 servomotors.i would like to follow a dark line. At the turning i would like one of the servo moves reverse from the other to take 'sweet' the turn. does anyone know how can i fix this subject with a logic circuit ? At my previous construction i built a logic circuitwith the following instructions. To move forward the robot at the output of the logic circuit i had logic 1 ,when i had logic 0 the servo stopped. how can i change this circuit????