UKHeliBob:
Using the outer walls to provide a distance measurement and keeping the robot parallel to them sounds like it could work.Is the objective to collect as many/all of the golf balls in the shortest possible time or something else ? Using the vertical and horizontal lines would allow you to collect 8 of the balls using a line follower and the distance of the outer balls on the lines indicates the distance to maintain away from the wall to get the other 4.
What you need to do is to work out the shortest path for the robot to travel to collect all the balls using the lines and the walls as reference points. What sort of size is the pattern and how big will your robot be ?
The design that my team has come up with involves driving down the middle of the balls and collecting the balls on each side of the bot at the same time. Basically you have 8 balls on a large outside square and 4 on the inside, smalled square. Our idea is to have the robot do a path in the middle of these two squares and when it senses a ball on the outside arm (on the "large square") it will swing both arms on each side to collect any balls there.
The track is 8'x8' with the outside perimeter of the 8 golf balls 16" from the outside wall. The balls on the out most "square" are spaced 36" apart and the balls that line up on the lines are 16" apart. We have already designed how to collect the balls on one trip around the track. Our robot is 7.5" wide before the arms swing out. Once they swing out, it will have a "wing span" of about 18". Provided the wall sensor(s) mounted on the chassis of the robot, it would have to read the wall from about 20" away.
Our task is to collect all 12 balls and deposit them in the middle box under a minute. Our goal is to do this in under 30 seconds. We think it can be done a lot quicker but that is the goal we have set for now. Its the reason that we are trying to collect all of the balls on one trip around so its quicker and less travel the robot would need to do.
*edit: the robot's dimensions are 11.5" long x 7.5" wide which is set by the design we have and then the height can be up to 10" but with our design to get the balls into the center box we will have a chassis plate about 4" high and then another, smaller, plate at about 7" high that will hold the micro controller and circuits.
BTW, the outside walls and center box are made from 2x4s