I've been making a bell crank mechanism as a downloadable to go with the mechanisms page. The idea being that you can find out how bell cranks work and what they are for on the mechanism page, then download and make your own for the full hands on experience.
Nearly done, it should be up tomorrow. I've still got quite a bit of work to do on the mechanisms pages themselves. I've been surprised and gratified just how many schools are visiting them, it is spurring me on to better things.