Beginner Arduino Robot - Table Edge Detection

A robot I made for a class that will try to detect the edge of a table and try to not fall off.

An article I wrote about the process: https://medium.com/@justin.en.ho.02/bot-olympics-development-of-an-autonomous-robot-9626ca034d99

Parts needed (most of the big electronic parts are in the SolidWorks):
Arduino
Ultrasonic Sensor
TT Motor Robotics Kit Wheels
L293D Motor Driver
RGB LEDs (Anode)
AA Battery Holder (holds 6 batteries) (you need the batteries as well?
Metal ball castor

Code partially written by Robert (Rob) Blain.