Last year we were introduced to Maya and tasked with making an orrery. The challenge we faced was trying to make gears that meshed together seamlessly and looked appropriate for an orrery, as well as how the gears would control the planets on the orrery. I was just getting to grips with 3D modelling last year, and this was my first experience with it, so it didn't turn out as well as I would have liked, but all in all it was a nice challenge.