A friend of mine at the nearby LEGO Store had some instructions for his favorite train: The Big Boy.

I took a look at them and realized pretty quickly that as designed what he had wasn't going to work well.

There were a lot of structural issues as well as illegal building techniques that need to be redesigned.

I thought it would be a pretty quick fix at first, but once I had to change one thing, a dozen other things down the line needed to get updated. Ultimately, I'd say a good third of the design changed before the final model here was mocked up.