Power for robot

I'm planning on making a robot with 2, 6V DC motors, a 4.8-6V servo, and an IR distance sensor. I have made and tested the code which seems to work, but my question is the power for the motors. I have a motor shield on my arduino uno. I'm going to externally power the servo, but I wanted to know the best way to power the motors. I've read that i can power them separately from the arduino uno by cutting the Vin jumper from the motor shield to the uno. If I were to power the motors in this way, I would have to also give power to the uno board. At this point it just seems like I have so many separate battery supplies that it seems unnecessary. Would it be better to keep the Vin jumper from motor shield to uno intact and simply supply the entire system (through either the Vin pin or Vin screw terminal on the motor shield) with its rating of under 12V? In this case, I would still probably externally power the servo motor, but I would have no more than 12V going into and running the board and the motors. And would this 12V be sufficient to run 2, 6V DC motors and an IR sensor? Any help at all will be greatly appreciated.

You would need 7V or more on Vin to power the Arduino. I think your best bet might be to use a rechargeable battery of between 7 and 8 volts. This can be connected to Vin to supply the Arduino and shouldn't be too high for the 6V motors. If you need to drop the voltage to 6 for the motors or servos you can use the forward voltage drop of diodes to drop the voltage.