Well, IMO: mechs are very cool. In fact, in just about everyones opinions, mechs are the shizle. So, lets discuss.
As far as mech are concerened, full movement and leg design is often considered unlikely for large crafts do to a single main factor: gravity. But, as a possible solution, if the main body was partialy or fully bouyent, legs could easily jump and clamber as they wanted. Think of an armored baloon with jointed limbs and weapons. As far as way to achieve bouyancy, the main options are vacume chamber, hydrogen, and helium (in order of effectiveness.) All have negatives, but H2 is the most problamatic...as it violently reactes with oxygen and other substances. Helium is heavier, and unlike H2 and a vacume, would be dependant on be refueled with more He for any that it lost through leakage. Vacumes have the maximal possible bouyancy, but a material capable of sustaing its shape and still be light enough to be plossible is a problem. With new materials like carbon fibers though, a ultralight self supporting vacume envelope could be possible I believe. If so, you could increase or decrease the size of the envelope to inrease or decrease the bounacy and as such, alow for lift and decent.
To me, this seems a plossible way to make large scale mechanoids...what are your thoughts? (On this and other issues)