I've been lurking around a month, so I'm already aware of some of those discussions. However my goal is to learn electronics by doing, so copying someone else would defeat the purpose.
Hmm. Just when I think I've got a handle on it, I make a weird discovery. If I raise the test weight up to any height, then cut the power - but before the motor goes into reverse I take the weight of the test load in my hand for a couple of seconds, then release it... the door doesn't fall! Completely repeatable. What is going on there? Is this just a borderline effect I wonder?
Unfortunately I've not yet found any worm gearboxes (with DC motors) which are cheap and have reasonable power consumption. Still looking.
Time for you to define "cheap" and the power limitations. Worm gear windshield wiper motors and stand alone worm gear motors seem to start at $15 surplus and on ebay. A black and decker 6v cordless screwdriver can be had at walmart for $10 or less.
Solid friction isn't linear, it has hysteresis.