Hey, welcome to Seiberton:
Warning: May contain nuts!I like these, but the missing limbs make them look a bit odd. I usually don't draw the detail on the second side limbs either when I'm designing, not wanting to repeat myself, so I just leave it at rough bubbles of where the arms and legs would go.
Your work could also use some more proportioning, try using a guide line underneath, first sketching out the "skeleton" of the 'bot, lines for the torso and shoulder and hip lines, lines/bubbles for the limbs and a circle for the head. Then you can build up the detail, ignoring areas you don't want to draw fully without compromising the drawing.
Check this out to see what I mean:
http://justicity-comics.deviantart.com/art/Cheetor-Prime-sketch-129940744http://justicity-comics.deviantart.com/art/RotF-Soundwave-interpretation-127953451See how the left hand limbs are there but in such little detail on the first one, and the base lines on the second?
The second one's actually what I used to teach a class on drawing robots using these ideas. I never got round to finishing it afterwards.
Hope I helped, but I really like the stuff you've got here, don't take the constructive criticism the wrong way ^^
I look forward to seeing more of your stuff, remember to post often XD