Using a regulator (or not) to power Arduino and motors from batteries

I am working on a wheeled robot made up of an Arduino 101 and 2 DC motors and I’m not sure how to go about the batteries.

I haven’t decided on the motor controller yet but I am between the Adafruit motor shield v2.3 or a cheaper controller (i.e. a dual bridge based on the l298n). I might go for the Adafruit since at a later time I want to add a stepper to the robot too and the motor shield also runs via i2c.

For the chassis I selected:

And for the motors:
Pololu - 100:1 Micro Metal Gearmotor HP 6V (or perhaps the 75:1 version)

The website I linked to also has a complete kit and they mention that their shield uses a 7.5V boost regulator for powering the Arduino from the chassis 4 AA batteries.

My questions are:

  • Are they using the step up because the nominal V of the 4 AAs is 6 (enough for motors) but the Arduino recommends a minimum input of 7V? or are they using the regulator mainly so that the voltage stays constant regardless of the batteries actually dropping (they won’t stay at 6 for long)? Or Both?
  • For a project like this, would it make more sense to instead use 2 18650s? This would give me a nominal of 7.4V and higher capacity
  • If I used the 18650s, should I still use a regulator?
  • Should I use another type of battery? My requirement is that I can use a rechargeable battery and if possible, I don’t want to use separate sources for the Arduino and the motors.

Thanks!

According to the Zumo Arduino Shield schematic, the step up regulator is used to provide 7.5 V for Vin of the Arduino, independent of battery voltage. You could also use a 5V stepup/stepdown regulator and feed the Arduino that way, through the 5V connection.

The motors run directly off the battery. You may be able to use a 2S LiPo cell pack for both, as the Arduino regulator should help combat electrical noise from the motors (but it is always a problem). I prefer NiMH batteries to LiPo, as they are far less finicky with charging and discharging.