Simple Design and Digital Prototyping Software
I've been making some very simple mechanisms for a steampunk Instructables series I've got planned, and have been prototyping using cardboard and paper. This has actually worked really well, but I'm a fan of the digital realm, too, and was wondering if anyone could recommend some simple, cheap (ideally freeware) digital prototyping software to help me eliminate (or minimize) the paper and card phase?
As I say, the mechanics are very simple. Cams, pulleys, levers, gears -- nothing more complex than bell cranks, linkages and basic drives. I think a scotch yoke is about as adventurous as it's got so far. So I'm looking for some nice simple software that'll allow me to build and test the mechanisms digitally, if such a thing exists.
I've looked at the likes of Autodesk and Blender, but they seem like a sledgehammer to cure a headache. Even something that runs online in a browser, or an iPhone/iPad app would be good (I've played some physics-based games on the iPad that would almost be ideal if they weren't puzzle games!). Any advice?