> A rather small motor with a lot of mechanical advantage can easily open a close a garage door, and if a DC or low voltage AC motor is used, it could do so quite a few times even if the power goes out.
Garage doors are actually fairly heavy. By balancing the weight with a spring, you do a lot of favors to your mechanical advantage systems. (Eg: less wear, less advantage needed, the door can open in a reasonable amount of time…) You also do yourself a few favors for when things fail. (Eg: you pull the safety release and it’s possible to open the door without the motor.) Finally, power isn’t free and motors aren’t either; A spring is a really cheap way to reduce the cost of both of these things.
Still need to store the same amount of energy. A counter weight or piston also has more opportunities for uncontained failure. At least when a garage door spring fails it is still constrained by the shaft running through the middle.
For what it's worth, I have also replaced my own garage door spring, and I really have no desire to do that again.
The risk isn’t just what the spring does but what happens to something caught in it. Springs can release energy a lot more quickly than a counterweight which can only accelerate a 9.8m/s/s, and therefore more risky to disable.
A few hundred points accelerating at 1g is still plenty of energy. It also comes with it's own challenges when it comes to releasing it.
It also provides a constant force, whereas the force required to raise a garage door linearly decreases the higher it gets. With the consequence that a garage door with a failed motor would slam into its stops over your head rather then into the ground. Followed shortly thereafter by the now liberated counterweight slamming into the ground.
True but by adjusting the angle you still end up with a fixed weight throughout the run. A spring force changes throughout the movement of the garage door and that’s chosen to match the unusual fact that the garage door’s weight changes as it’s gets progressively rolled up onto the top rails.
A fixed weight but not angle means the force varies. Cut the cable and acceleration would therefore also vary with that angle along the track.
Springs make a lot of sense from an installation perspective and can be easily tuned to match the specific door design, but if I was working from scratch on a DIY project I would prefer to use a counterweight if there was somewhere it fit.
Plus a counterweight is a big fat weight hanging in midair, so it's pretty obvious what will happen if you let it fall (and where it will land), whereas with a spring it's much harder to tell whether it's under tension or relaxed, and what it might do when the tension is released...
Maybe there could be a mechanism that lets you decouple the spring from the door and instead connect it to a worm drive, which would then be used to take tension off the spring using a power drill, all while it's completely contained in a steel housing.
Sure, but then you have to put the counterweight somewhere which would occupy garage floor or wall space. And the counterweight track would have to be enclosed for safety.
garage door springs are safe if you are careful and you use the correct tools and procedures. the instant you take a shortcut with these, you increase the likelihood of a bad outcome.
so, don't take shortcuts, and don't do the work if you don't know what you're doing.
the professionals know this and that's why we pay them, but they're not special creatures with special abilities; they're people who understand that this is a situation which can bite you, and they act accordingly.
Just about anyone can change their garage door springs, if they do so correctly.
Garage doors are actually fairly heavy. By balancing the weight with a spring, you do a lot of favors to your mechanical advantage systems. (Eg: less wear, less advantage needed, the door can open in a reasonable amount of time…) You also do yourself a few favors for when things fail. (Eg: you pull the safety release and it’s possible to open the door without the motor.) Finally, power isn’t free and motors aren’t either; A spring is a really cheap way to reduce the cost of both of these things.