…the hourglass in the middle of Hermione’s time turner (Harry Potter) rotates along its long axis. What’s the point of that??? If it rotated around its short axis instead, it could set 3 units of time instead of just 2. You’d think wizards would know these things.
(I’m designing a time turner and this detail is bugging my engineer half!)
The images I found show it in a frame that rotates about the hourglass long axis twice and then also around its short axis, like a gyroscope. I think you get one time set per axis. Plus, three time sets would have been really hard to keep track of. You would end up with some kind of timey-wimey non-linear paradox issues one would think.
Did you just mix fandoms?!
Probably. 
You have to use every tool at your disposal to get a good explanation!
Yeah sometimes you really gotta use the force.
With a really big hammer…
More to the point, why didn’t she use it later to go back in time to save Dobby or Dumbledore or to find out where the horcruxes all were or…
Gyroscopic precession.
You can’t turn on the short axis without also affecting the input on the long axis, thus results would be unpredictable.
Do you even engineer, brah? 
Imagine if the giant eagles had just flown the Hobbits to the mountain in the first place… I have always been annoyed that the needs of the story teller drives all the stories to have their folk make decisions they should not make otherwise, and then actual people use the stories to make their own decisions. The Utopia that there were no problems and everything worked might be the ideal for folks to live but it would make the worst novel ever.
Those “just in the nick of time” life saving plot points always irk me. I’d have demanded to know where the eagles were before or why the heck Hermione hadn’t just solved everything were I a character in either book.
I would’ve written a strongly worded letter at the very least 
Conversely you know that there is almost never any real danger to the hero as the writer (who is the real god in the piece) will be on hand to save their tail at the last minute.
Serials, of course, are the worst as the bad guys always win at the end of each show so they can show how the heroes get out of the problem in the next, and if the season gets canceled, the good guys never get to win. I think that a general malaise can be in part to serial stories that always turn out badly as folks take in dozens of them at a time.
You might be on to something, there!
The tendency to use these one-off tricks to save the bacon seem a bit lazy on the writer’s part - it’s like they wrote themselves into a corner and needed a Hail Mary to get out. It’s even worse with serials because they don’t incorporate that miracle thing into the ecosystem of their fictional world and cause disruptions in the story continuum. If it’s planned then it crosses books in the series (like the clothing thing for elves in HP) but if it’s never seen again it’s pretty apparent it was an unplanned response.
You guys will eithe love or hate tv tropes.
For example @jamesdhatch is describing deus ex machina.
I’ve found time here and there to work on my time turner. Finally got a prototype printed, and, shockingly (for a first try), it works really well!
Except for the turning back time part. Darnit. I could USE that right now.
You need to post that one in the MOAG category for sure! 
I want to do a nicely finished one first. 
Inspirational. Did you use an hourglass that you already had on hand?
I ordered one I liked from Amazon. This design has been “cooking” in my head for at least 6 months.
