[Photon] Controlling DC motor(s) and powering the Photon

Greetings everyone !

I’am new in electronic, and I don’t have really good knowledges. I learn by my self on the internet.
My goal is to build a small and low cost robot that avoid objects with my Photon.

I followed this tutorial and I am trying to adapt it to my Photon : http://eskimon.fr/285-arduino-601-le-moteur-courant-continu#728481 (Sorry it’s in French because I am)
So, I have some questions about this wiring (See picture below) :

U1 : L78L05ACZ (datasheet) (I could not find the right componant in Fritzing)
R1 : 100 Ohm resistance to drop the current from 100mA to 50mA
IC1 : L293D (datasheet)
C1 : 0.1mF 20V

What I want :

  • Power the photon and motor(s) from 3xAAA battery (beacause I have a small robot chassis with a 3xAAA holder)
  • Use Rx and Tx to do PWM on each motors (it will be a 2WD)

What I don’t want :

  • Buying battery/motor shield that cost the same price as the photon or higher

What I know :

  • Photon has a Vin-max of 6.5V (I could not find if there is a max current input)
  • The L293D (pin 16) Vss works with 4.5V
  • The L78L05ACZ drop current from the battery to 4.5V and 100mA then a 100 Ohm resistance drop it to 50mA so I am below the max Iss (60mA) of the L293D

Questions :

  1. Can I power the Photon like that ? If not is there a solution to do this ?
  2. Does it seems to work ? If not what is the problem ?
  3. Can I do the same for the second motor ? If not what kind of modification does it implies ?

I am open to any constructive criticism.