Cartoons

[Peter H.M. Brooks]

I'm going to be making some cartoons for a film - they're 2-D 
animations. Imagine a cartoon of an internal combustion engine that runs 
as an animation with the pistons moving up and down, the petrol and air 
mixture entering, the explosion and so forth, they'll be similar to that.

I'm wondering if Omnigraffle is the best tool to use. Any suggestions?

I'd really like to be able to specify to some bit of software which bits 
move, what their direction of travel is and have it do the animation - 
do you know anything that could do that from an omnigraffle file?