[argvargc]

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.)

[ridaj]

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.

[grishka]

> 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.

[martin_a]

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. ;-)

[amelius]

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

[martin_a]

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