Cruise Controls R&D Engineer interview questions

First I received an email to elaborate on other work and projects I had done in the field of controls. Once those answers were accepted I was given a technical challenge that I could complete on my own time. After the challenge was reviewed I had phone interviews with two of the engineers on staff. When it came time (I assume) to decide if I was a good enough candidate to fly in for an on site interview, I was informed they were no longer interested.