I'm wondering, would it be possible to build something like this with the springs:
<img src="http://i35.tinypic.com/flvfio.png">
so that only the top moves up and down, instead of the springs acting like hinges and the top part just flopping over to one side? Like, by restricting their angle to just 90 degrees or something.
In the physics behavior you have "No rotation" option.