Awesome robot! 2 things. Firstly, the shadows, especially in the crutch area could use a little improvement. Secondly, the arm/hand on the right looks a bit odd.  It looks like you are trying to emphasize a larger false perspective hand arm on the bot.  However, it didn't come out perfectly.  Also, I would recommend using a dark gray color instead of the black outline. Then, add a layer of white to emphasize the border. Otherwise, the bot looks great as it is!