Don't be too harsh on yourself. There are so many artists/illustrators out there making a living from what many people would call "bad drawing skills". Look at David Shrigley for example. He's one of my favourites, and his style is just, well, terrible! Similarly, Gemma Correll's work isn't highly polished and anatomically correct in every way, but she's a very popular and successful illustrator.
Their work isn't about how technically skilled they are though, it's about the humorous observations and situations that they illustrate. And that's what illustration is about. Making something clearer, quicker and easier to understand through visualisation.
Maybe you should switch up your approach to "Droid A Day" and turn it from a sketching project into an illustration project. You've got the technical skills for sure, but I think maybe you now need to work on the thinking side of it. Maybe scour the web for interesting or unusual news stories from that day and illustrate something about that through robots. Maybe just take the headline and draw a little illustration that takes that out of context and turns it into something new and weird. For example, this is currently on the BBC's front page – "Gerrard faces 'biggest month ever'"
Obviously the headline is talking about pressure and expectations of Stephen Gerrard, but it could easily be about a robot called Gerrard stood looking at the "biggest month ever". What would that look like in an illustration? How do you visualise a month in a physical form? That's your job.
Your robot drawings are awesome, don't be in any doubt, but from what I've seen they just appear to be sketches enslaved in your books. You need to apply them to something, give them some context and free them. Maybe even mess about with screen or riso printing some robot patterns or prints to get yourself out of your current way of thinking and produce something tangible. Hell, try DIY printing techniques if you can't find a local print studio. Make a few, book a stall at a local print or craft fair and try and sell some stuff. I bet you'll meet some really inspiring and insightful people on the way and I can guarantee they'll probably feel the same way about their own work and skills as you do about yours.
Thanks so much for taking the time to reply. Your idea has proved pretty popular, I've taken tweet suggestions from people over the last week or so - using their words and ideas to create robots and illustrations. It's quite a relief to free myself from that aspect of the project occasionally.
At the moment one of the problems I have with the project is a real lack of time. I started it when I was pretty quiet on the work front, but soon afterwards got a contract in central London. Now I'm kind of restricted to a little time at lunch and a bit of time between eating dinner and going to bed. I think I'm kind of viewing it now as a way of generating ideas, and at the end of the project I'll have a reservoir of stuff to draw on (pardon the pun).