Thanks! I'll take a look. Including flexible bodies shouldn't be that difficult. If the dynamic_symbol supported including spatial variables, you'd be most of the way there. That's assuming one is interested in the PDEs. 

I've done an implementation in Maple that supports using a FE discretisation for the spatial variables (although mine only supports beams at the moment). Given the structure of PyDy, it will take some work to see how I could adapt what I've done to it, though.

Oh, one can also look at: http://hdl.handle.net/10012/4127

for an approach to handle large strain of curved beams. It was designed to be used to analyze hockey sticks.