Combination of Wires of two DC motor giving Output current.

I wanted to make a electric Generator. For it , I used a 2 DC motors(suppose , A ,B ) in a Line and connected their rotors . I took another DC motor (suppose ,C)and connected it's rotor with one of rotor of DC motors I already Connected. Now I started to give current to motor C . It rotated the rotors of Motors, A and B . Now , I am confused that in which combination I will need connect the wires of Motors A and B so that I may get thier combined voltage .
Please Help me in Solving this Problem.