Did this for Mainstay Studio. Not my characters. Didn't have a ref for the robot, so it looks a little shabby. But I worked extra hard on the coloring. Left the upper BG open for possible title / studio info. Couldn't find a fitting category, this is the best I could choose.
PENCIL sketch on 8x10 cardstock, 3 hours
CG with Photoshop + mouse, 7 - 9 hours (can't remember)
Ugh... can't wait till school is over so I can relax.