Quick background : I am a mechatronics engineering student on my first co-op at a great company. They have pretty much told me to make a mobile robot(controlled by a wireless controller) that will carry an arduino based sensor module(that I made) as my first project. My boss wants it to be all me, and only wants me to give him part numbers so he can order them for me. Therefore, for this project, money is not a constraint. Keep in mind this is simply an R&D project/prototype.
I have lots of questions, as I have never actually made a robot from the bottom up before, nor do I have much knowledge on motor dynamics/motor control. Before anything, here is a list of parts that I have so far.
Microcontroller: Arduino Mega 2560 R3 - to control drive base Arduino protoshield(not buying, have one lying around) - for prototyping, general cleanliness
Wireless Joystick Controller: Arduino Wireless Shield - to connect Xbee transeiver to arduino Xbee-Pro XSC S3B(wire) - to be used in wireless controller Xbee-Pro XSC S3B(wire) - to be used on arduino board Wireless Controller(arduino compatible) - to be used with Xbee pro http://www.robotshop.com/ca/en/wireless-gamepad-arduino-v2.html
Hardware: Vex 2-Wire 393 DC Gear Motor w/Motor Controller 29(continous rotation servos, no hbridge required) - motors for drive base http://www.robotshop.com/ca/en/vex-2-wire-393-dc-gear-motor-motor-controller-29.html
Vex 12" Square shafts - shafts for VEX motors Vex Shaft Collars - collars for VEX shafts Vex Wheel Kit -assorted size wheels Vex Delrin Bearings - to mount motors
First question: Do i need a motor shield, that I have read so much about? And if I do, why do I need one? Can the motors not be simply controlled by the analog pin? Also if I do need one, which one would I need : https://learn.adafruit.com/adafruit-16-channel-pwm-slash-servo-shield/overview, or https://learn.adafruit.com/adafruit-motor-shield-v2-for-arduino
Second question is about motor batteries: What I understand so far is that it is not good to power the arduino and four robots using simply one Lipo 7.2V battery. THe motors themselves are rated at 7.2V. So do I need a seperate battery for each motor, or one for two or etc? How would I figure this out?