I remember playing with a differential engine in those Lego gear sets many many years ago. When you have a bunch of the pieces lying around and free time, you'll probably accidentally make a differential too.
As for this video itself, I've seem it a few times, and it still really does amaze me how much care was put into this. I assume the video is government funded, and it kind of makes me sad to realize that they had the capability to create educational videos of this quality 90 years ago, but it wasn't high enough priority to broadly apply to the general masses.
The video was made by the Jam Handy organization. They did videos for several car companies, and sometimes a consortium of them, is my understanding https://en.m.wikipedia.org/wiki/Jam_Handy
That would explain the abundance of available mini-models that they could machine.
That does take the wind out of the sails of the argument that it could've had a broader focus than just the differential engine. In that case I'll shift my dismay to "90 years ago, videos of this caliber were possible, and yet educating people on a broader scale didn't enter the minds of any entity which could've afforded it."
As for this video itself, I've seem it a few times, and it still really does amaze me how much care was put into this. I assume the video is government funded, and it kind of makes me sad to realize that they had the capability to create educational videos of this quality 90 years ago, but it wasn't high enough priority to broadly apply to the general masses.