My (over-engineered) version of a smooth garage door
I saw u/propertyProphet 's post about their garage door having issues with flashing and it inspired me to make a contraption-based door with minecarts. I know this has probably been done before, but this is my version which features a smooth closing system.
It works by using the adjustable chain gearshift to ramp the RPM of the bottom fan to slowly lower the minecarts together before shutting off and letting them drop. Without this, each layer just drops individually and it doesn't look like a single connected door and ruins the aesthetic. By decreasing the fan RPM, the carts hover at a slightly lower height, allowing the next minecart to fall into the stack before it lowers some more to make room for the next one and so forth. After ~6 seconds, pretty much all the carts are in the stack and the fan can be turned off and let the door drop closed.
Since you can't automatically control an analog lever, I had to get creative in how to adjust the redstone signal for the chain gearshift. The RPM ramping system uses a chest filling up with swords with a comparator to measure its capacity and it sends the redstone signal to the chain gearshift via a link. The gearshift is not on the source of rotation so it goes from 1.0x - 0.5x of the input RPM, so it starts from 80 RPM and ramps down to 40 as the chest fills with swords. After that, it switches to the third motor which is set to 30 RPM which lowers it some more, and then it turns off.
There might be easier ways to do all this, but I like how it turned out.