For those of us who are on a budget and can't afford to buy SolidWorks or AutoCAD, I like to offer these links, available to all students.
SolidWorks, is a sponsor of Battlebots, FIRST, and many other robotic competitions. You can sign up to get their software, free of shipping charges, at the following website, where they will send you 10 free license for a year. Software and license keys included.
General sponsorship website. Click on "Click Here to apply for Team Sponsorship!" to sign up.
AutoCAD, is a bit more tricky. First you must be a student, with a valid .edu email address. Second you must sign up for the program, and then you have to download the software, after which they will email you the key.
Click on what version of AutoCAD you want and follow their "easy" steps.
Hope this helps in your robot building, and now you have no excuse not to create awesomeness.
P.S. Will Bales found the AutoCAD website, so all credit goes to him. He posted the link somewhere, but I thought I'd repost it as a I couldn't find it on the forums.