: : It depends on how far back you go. In The Fall of Gondolin (Bolt II), there are indeed 'mechanical' creatures in the shape of dragons which were hollow (so that they could act as troop transports) and could breath fire. Yet, while I have always preferred BoLT I & II over The Silmarillion, most people do not consider them canon.

: : There are mentions of both Sauron and Saruman making use of 'engines' (and possibly some form of black powder explosive), although I don't recall them being described in detail.

: I beleive that these cases were more likely to be based on magic than physics (customary to Tolkeins work). The 'hollow dragon' is a good example of the 'organic machinery', a body without a soul. I was interested in what kind of troll-like races might Morgoth have had in store?
: Maedhros

The creatures were specifically stated to have been made of metal (bronze if I recall correctly) - how they worked (via magic or 'technology') is open to speculation.

Regarding Morgoth, I believe that he had become rather tapped out by the end of the First Age, having invested too much of his power in his creations. Perhaps someone who has read Morgoth's Ring could provide more information. But, I think the point is that he probably didn't have anything up his sleeve by the time of the War of Wrath (with the exception of the winged dragons). The creation of a new Troll breed fell to Sauron.