Hello there,Hackmodford
i read your project and i think what you are trying to do is awesome let me try to help you as much as i could,
urm first of all i think you are able to make the ping)) sensor to work rite, in what range is the max and the min that it can return. use that as a source of your mapping,then translate that to your motor. why not use a pager motor. its small and i think it provide a good vibrational force.
anyway this may help you a bit on the programming part
int Pingreturn= //i dont know this part in your setup
int speed = map (Pingreturn,Min,Max,255,);
analogWrite(Motorpin,speed);