I am looking to do Phd in robotics in the future so that is my first choice, I have also done some work in image segmentation so if I can't find a good robotics thesis topic I would choose one related to image segmentation. Where can I find good topics? or do you have any suggestions?
edit: robotics wise I have built a rubics cube solving robot and some simple robots
You need to talk to the teachers at your university. They'll have plenty of ideas of the right sort of scale and help you to pick one that you'll be able to do well at. Remember that at the undergraduate level, it's not just about picking an interesting topic, but also about doing a good write-up of your work and in a very short time. (You'll definitely not have enough time to do a good job in a truly interesting area; that's what a PhD is for and you've got to get there first.)