I used to have one of these, but left it above the radiator. All flaps warped beyond repair :( So if you're going for resistance to harsh environments you'd have to source a better material for the flaps, at least.

Hm, after watching and listening to videos of these displays at airports and train stations (don't think I've ever seen one in person), I thought the flaps in the commercial ones were made of thin sheet metal because the flipping sound was somewhat sharper than the OP version.

That sparked an interesting idea: would these work in a zero-gravity situation (mechanically I mean), and if not, how to adapt them so they would?

(And agree with the nostalgia - I'm sure for many the sound is associated with a quiet anticipation or excitement of embarking on a journey.)

I think they'll work... Somewhat? As the card is pushed through the face, there's a small amount of spring energy that it stores by bending, which gets released when it makes it through the opening and propels it forward + downwards. Normal gravity just adds to that motion and keeps the flap moving down. Zero g doesn't help as much but the card should already have momentum out of the gate. In zero g the problem may be more dealing with the rebound as the flap hits the bottom of the frame - it may bounce back up and float. May need some dampening or magnetic trick to keep it down...

In any case they probably won't work upside down.

> how to adapt them so they would?

Add rotary springs (is this a valid term?) to the flap hinges so they're forced down once released from the top edge of the frame.

They probably won't.

After a flap has passed the upper lip, which is kind of holding it back to have a precise "flipping point", gravity will take care of moving it down.

No gravity, no flap. ;-)

You could use suction or flow of air to overcome this. Or perhaps even a spring.

Or just some kind of display that does not rely on gravity, yes.