HazardsMind:
Are you using a UNO or Mega? I've done it with 2 PWM motors and 1 regular on/off motor. The range is however far the controller can go, that's it.
I am using the UNO and my four motors are connected so the arduino only thinks there is two but if you don't have problem whit sending me the code and the schematics then I would like to have it.