Gulp35- First off good luck with your educational endeavors.
However, your first mistake applying to MIT...go to Caltech the weather is much better.
Just kidding MIT is obviously one of the premier institutions on the planet.
Look these people see a LOT of application sent in by very smart people. You need to make sure you have something that sparks their interest and then keeps it. superart is correct they want someone who thinks outside the box. Bill is also correct that they want to see you have an above average grasp of basic engineering principles.
If you are going to use your "rig" as something, you created keep in mind that function and form are important but aesthetics are only good in pictures. The meat will be in the functional benefits of your modifications.
You might convince grumpy old BillA to help you with your technical writing.
Good Luck