I have did some research and I came across an Arduino Radar.
Please refer to the link below.
So from this video, can I assume that my concept can work?
HOTeddy:
Here is my concept of object finding.For example, it wont approach the fence enclosing the area as the ultrasonic sensor senses that it is an object of width larger than 3cm, it will reverse and go another direction. By this way, it will always travel randomly in the enclosed area. When it sense a 3cm object (pingpong ball) it will approach it, collect and then sense the surrounding again.
So to sum it up, the machine will go another direction when ultrasonic sensor senses object is greater than 3cm and will approach it if it is less than 3cm.
Arduino can sense object size and I would need to write a code for my machine to approach it (which I have no idea how to start).
I greatly appreciate all your active replies.