So I clicked this to get a good look at several of your OCs at once and not for the tutorial, but this is a really awesome tutorial for robotic characters or anything armored in general and now I can't not fav it. You're an awesome artist. ^_^
Am I to assume next you'll talk about continuity style? Which universe the character is in has a huge influence on the character's appearance as well. For example, G1 characters are blocky, simple, and ignore at least half the stuff in this tutorial. Energon characters are boxy. Movieverse characters have a huge amount of detail, while TFA characters are cartoony in appearance. Using a custom universe, of course, offers the most flexibility.
No I will not go into these styles - I only focus on general aspects of TF designing in the way I do it(which is directed into Prime-verse), as mentioned in the first few lines. I'm not that deep into TF that I have enough knowledge about any continuity to be able to tell people how to draw them correctly. The information I give can be applied to any continuity - like visible vehicle parts, that parts don't collice or block each other and logical joints and the positioning of certain parts. I'm not a TF professional - my tutorials show only my personal way of doing things and not how they have to be done for each existing TF series. I can only offer general information ^^
A tutorial to help you design characters, especially transformers......FINALLY!!! I mean, I've found these things before, but I've always admired your Cybertronian Works! This will help me BIG TIME. Now...just need to buy more sketch paper...