I have recently purchased a Bareduino328 which I am powering with 9v. I am regulating the power to 5v as per the instructions here: https://www.virtuabotix.com/bareduino328-plus-regulate-your-bareduino/
The problem I have is that the Bareduino seems to reset itself just seconds after starting a 5V DC motor. I believe the problem is noise from the brushed DC motor that is causing the microcontroller to brownout, but I am not sure how to fix it. I have no issues starting and stopping the DC motor using the Arduino Uno official board. I am using a P2N2222AG transistor (and a flyback diode) to control the DC motor. Has anybody tested the use of DC motors with the Bareduino setup?
I have found that most of the motor controller shields and even the stand-alone motor controllers filter out noise very well. There is an inexpensive kit that sells on Amazon and other places that sells for $11. It will power two motors at 1 amp.
Alternatively you could build your own H-Bridge, but if this is your first project I would start with a working one first so you can get used to how they work. I used to have the exact same problem when I tried to make my first pic based robots and attempted to directly control motors.
Doing a few hours of reading on how H-Bridges work will likely clear up a lot of questions about why your circuit is browning out, and behaving erratically. You can also look at the online datasheet page for the Versalino MotorMaster since it has a bunch of H-Bridge goodies, and was built to work specifically with the Versalino/Bareduino hardware.
Hope that help!