Next bit to address on the Door Droid is the strange, almost medievial side parts. They're quite hard to make out but seem to be some sort of chain/gearing affair, with spikes all over:
For the main bits i'm using cotton reels.
I measured the distance between where they'd be going and drilled two holes that distance apart in some Plasticard and bolted two reels down.
I then eyeballed where the lower one in the middle would be and again bolted another reel there.
And you can i've rivetted a strip of Plasticard between the two upper one's, looped around the bottom one.
I think the original is a definete chain affair, but i'm not too bothered about using a solid strip of plastic as, with all the detail on, i don't think you'll see too much of it anyway.