I Replaced Deadly Garage Door Torsion Springs and Lived to Tell the Tale
truetex.com
truetex.com
The house I lived in as a kid had a solid metal door hinged about 3/4 of the way up, that you could lift by hand with relatively low effort, and at the top position it would balance on its own weight. The electric part was just a roller chain attached to a short lever, which also happened to give some resistance to the closing movement.
It worked too, after about 50 tries per side! With the confined space, and only two hands, getting those wires to stay in the spiral groove of the pulley while also hooking them up to the door is... error prone. Can't even ask for help because the raised garage door blocks access.
However I got it done in the end, and the spring was never tighter than you can wind it with one bare hand. The garage door works fine.
I did watch someone do it the proper way (wind it to full tension with the door down) and agree, you could hurt yourself that way.
If only the rest of the Internet had this level of content.