Right now you can get Autodesk Inventor Fusion for free right here.
In school I used Inventor Professional everyday, it was one my favorite pieces of software. I was really excited when I saw that I could download this version for free. I have been using it the last couple days trying to design a two wheel balancing robot.
My first impressions is it is a l lot like the software I used in the past. Some things don't seem as intuitive, so there is definitely going to be some learning curve till I get fully comfortable and efficient using the software.
One thing I don't like about it though is that there aren't any assembly files in this software. It used to be that you can create all your components in one file type and assemble them in another. But that isn't the case with Fusion. You still have all the same features but all squeezed in one interface. I think Autodesk touts this as a feature but I'm not sure I like it. It may take just some getting used too.
But if you're looking for some full featured modeling software you can't beat the price. I'm not sure how long the software will be available for download but should be usable till next year sometime.