To do this, I've had to create using illustrator to ink the character sketches for the final design.
Taking sketches from photoshop, I had to import them into Illustrator and ink them in. The result on the front model came out looking very tidy compared to how it would if I drew up the inks in Photoshop, which given he's a robot would probably be more appropriate than looking very sketchy. The process took much longer than it would have in other programs, but the results are decent enough that I think it was worth using. The basic inks were also masked off so that it appears cleaner when it was imported into photoshop and coloured up.
When brought into photoshop I applied basic shading to the character, I thought about giving very painted shading but given it's a robot I wanted very simple shading to make it look a bit cleaner than I do more organic characters. The bit which I really enjoy about colouring this character is that I was able to use some textures to try and give an impression that he's made of metal. I created a brushed metal texture in photoshop which I applied to the grey areas in addition to finding a fabric texture on the net which was applied over the top of the hat. Overall I think the character's come out looking alright, I'm tempted to go back and alter the shading of the character later but I would say that the inks at least have came out looking rather tidy and uniform thanks to the straight lines Illustrator is able to make.
UPDATE: Decided on some new shading, looks much more detailed and less like someone used the burn tool. looks slightly more cinematic and also has details on the tubing and the brush on the end of the character's hand.