3. Transmission angle y pressure angle a (传动角与压力角) Fn F b F /c B By 从动件 follower B What is the relation between the F and Fn or(el What is the function of the f& f3. Transmission angle  & Pressure angle  （传动角与压力角） What is the relation between the F and Fn or (Ft ) What is the function of the Fn & Ft follower