i've had a similar thing happen in the way of having an idea of a really good invention only to discover that it had already been done. one time when i was like 10years old i was messing about with magnets and was totally amazed by the whole negative repels negative and positive repels positive thing, and being a kid i was into 'back to the future' quite alot. well i was trying to think up a way to create a car that could fly, or hover, and i thought of a way to do this by having magnets along the road and magnets under the cars.
i knew this wouldn't work because the cars would fly off the road, there'd have to be sumthing like a track, to keep the cars over the magnets. i couldn't think of an efficient way of doing this so i thought about doing the same thing but with trains. magnetise a train tunnel and have the outside of the train give off an opposite magnetic charge. since the train would be contained within the tunnel it'd hover and it'd move as quite a fast speed too.
later i found out it already existed in japan as the magnet train. damn them!