If you've never had the chance to read an issue of Brian Clevinger and Scott Wegener's Atomic Robo
series, you should really go and do that. It's a perfect blend of action and fun snappy dialogue.
Robo's design is difficultly simple in nature. There's not much to it but it's quite specific so you have to get the proportions just right (especially in the face) otherwise it'll look like an Atomic Robo stunt-double.
I wanted to draw a full figure instead of a head sketch and decided a bit of forced perspective and a staircase would be fun too. Combine that with the difficulty of doing robotic parts in perspective and the whole thing took just over an hour of noodling away to do, stopping only for e-mail answers and a snack.