One of the most exciting things about science fairs is the multitude of working models that you get to see at them. The thrill of seeing something that you made actually do what you wanted it to do can give you quite a high. Putting science into actual practice is what the whole deal about science fairs is.
So why not start early this year and pick up a proper working model for your science fair project. It can be something as simple as a conductivity test for metals and non metals. Or something as complicated as a remote controlled robot. There is no limit to what your mind can imagine as your science project.
So sit down and think of a list of things that can be made into working models. It can be a robotic arm which can pick and stack blocks. Or a car which you can control with a remote. Or even something as complicated as a robot that can climb stairs.
On paper there is no limit to what you may make. Try making a submarine! The only limiting factor will be the time and resources that you have at hand. While some projects are easier to make and will hardly take any time, if you are starting a more complicated project, make sure you do it as fast as possible.
It is always good to finish off the project a couple of days in advance so that you can see if any modifications are needed. It will also give you time to work on the project report, the display board and your presentation script. All of which are important components.