This one was a little tough. With regular portraits I can just take a photo and add some gears or hydrolics and metal plating and come up with an android look. With the random robots, since I've been doing it so much lately, I can make it up on the fly. Designing Transformers is a different animal. I went through about 8 pages of sketches just to get the design down, but I think it was worth it.
For reference, here are the motorcycles I used.