yup, however they all turned out to be crap.
one that i made that actually did work, but it did not work well enough. was a clean energy generator. a generator designed to generate electricity from the kinetic energy given off by waves, waves of water deep out in the ocean, a bobbing motion. If you made a mile by mile patch of them out in the ocean, about 25 meters tall by 5 meters diameter, you could generate a fair bit of power, but not enough really.
its basically like a load of hoops, with plastic balls inside the hoops that use the tube as a kind of road. inside of the plastic balls, magnets. the magnets run round and round inside the hoops, and the hoops has sections of copper wire coiling round the hoop on the outise.
a hoop with ever decreasing sizes, but not tube thicknes, like a zero inside a zero inside a zero. then layered to make towers.
you could maybe even put solar panels on the parts that stick out of the water
but really, all i ever managed to do was get a small bulb to light up with a crappy first try made out of old water bottles and tape and stuff.
there is a bit more to it than that, but you get the general idea