to view all the posts i did on this robot, please check my g+ profile,
my original intention was to build a line follower robot, until my wife's household chore caught my attention. from then my focus was on creating a robot similar to roomba, minus the vacuum. :]
the original design was a bit of a bulky wiring, but it worked well, running only on a single 9V battery to power the arduino uno, motor shield, and an ir sensor. then i read through some posts that this was a bad idea so i had to split powers for the arduino and the motor shield, and the mop section also got gave up after bumping several times at high speeds.
the 2nd design had a flaw which i didn't think through. i placed all components on top of a flat plastic plate which meant that there was more surface area in contact with the ground. this meant more force from the motors to move it. failed.