Ft Worth Scinece and History Museum- Special exhibit of Da Vinci machines. These were found in his notebooks as small drawings and someone built them on a small scale so they could be seen around the world. Some don't work, like this air screw.

Some were built on comission for a war

Some were kinda cool ideas.. like this paddle boat

Here's a copy of one of his notebooks

Here's a video of a simple machine that did work. Some of his "inventions" were improvements over the machines they were already using.