I know cadima here on the forums does some amazing work in CAD. He designed a whole CRT if I remember correctly, as well as a whole center differential.
You should try designing a slipperential... a differential with a slipper built in.
I am sure Mike has a patent on it since he is the one who originally designed/makes it, so no one else can make it, but I am sure it would be fun to design a similar version.
