HN Theater @HNTheaterMonth

These old-school education videos are such a treat. One of my favorite is on differential gearing - https://www.youtube.com/watch?v=K4JhruinbWc (apologies about the clickbait title)

⬐ Arnavion

https://www.youtube.com/watch?v=yYAw79386WI is the non-clickbait-title version, hosted by the channel with other popular recovered films in the same genre.

Reminds me of https://youtu.be/K4JhruinbWc?t=110

⬐ throwawaymath

That was really great, thanks for sharing!

My favorite: "How Differential Gear works" (1930s)

https://www.youtube.com/watch?v=K4JhruinbWc&t=1m50s

I've never understood why these old instructional films so often seem much better at getting things across and making them stick in my mind than more modern material.

A couple other examples.

1. A 1959 film from Bell Labs on wave behavior that made standing wave, reflections, energy loss due to impedance mismatch, and impedance matching much clearer than anything else I've seen: [1].

2. A 1937 explanation of how the differential in a car works: [2]. Here is another upload of that which is lower resolution, but has more from the same source in the sidebar [3].

I suppose it could be something akin to survivorship bias that makes old educational films seem so good--the bad ones don't get remembered 60 years later.

[1] https://www.youtube.com/watch?v=DovunOxlY1k

[2] https://www.youtube.com/watch?v=K4JhruinbWc

[3] https://www.youtube.com/watch?v=yYAw79386WI

Neat site. My father was a mechanic and thus I should know all of this stuff, but I wasted away my life behind the keyboard instead :D

I often find videos do a much better job at explaining some concepts. For example, the section on differentials:

http://www.howacarworks.com/basics/how-the-transmission-work...

After reading this I feel none the wiser. Whereas after watching this ancient Chevrolet training video from the 1930's I feel like I completely understand how diffs work:

https://www.youtube.com/watch?v=K4JhruinbWc

⬐ AlexMuir

I'll embed that video shortly.

⬐ nogridbag

Previous HN discussion on the diff video if you're curious:

https://news.ycombinator.com/item?id=8513209

Also, a great video explaining the working of a differential:

https://youtu.be/K4JhruinbWc?t=110

Fantastic!! High-quality educational videos like this are hard to come by. Here's another retro tutorial that really stands out in my memory (differential gears): http://youtu.be/K4JhruinbWc?t=1m40s

⬐ mutagen

Nice to follow that with this short video illustrating how one type of locking differential works to eliminate some of the disadvantages of an open differential.

https://www.youtube.com/watch?v=MCxqUJCZGNU

⬐ pkulak

So, one wheel starts spinning, and then, at a certain speed, it gets immediately locked into the other wheel which isn't moving at all? How does that not blow up the entire differential?

⬐ bri3d

With a hard-locking differential ("lockers", generally used off-road), engagement while one wheel is spinning is ill-advised. They're generally toggled on at low/zero speed by the operator in anticipation of a traction-loss situation.

The variety of differential which does not immediately lock one wheel into another is http://en.wikipedia.org/wiki/Limited-slip_differential .

⬐ HeyLaughingBoy

Yup. And they typically have to be unlocked when not needed as it is almost impossible to turn with the rears locked. However, with pneumatic or electrical operation from the driver's seat this is pretty convenient.

The type of locker I'm more familiar with takes a different approach: the rear end is locked by default but unlocks when it needs to. e.g., going around a turn causes the outside tire to turn faster than the inside one, and the teeth in the locker are angled so the speed difference causes them to cam out and decouples one axle shaft from the diff, letting it spin independently while the inner axle shaft is under power.

I had that system in my Toyota pickup and even in 2WD, it was absolutely unstoppable offroad.

⬐ draker

For manually operated lockers the axle shafts have to be moving at the same speed or with very little difference in speed to be engaged.

>Only engage the Eaton ELocker™ differential while the vehicle is stationary or operating at speeds of 3 mph or less with minimal wheel slippage.

This specific locker (Eaton G80) is self-engaging up to a set speed which is intended to prevent this from happening, though it has been known to occur.

>The G80 can be very effective when used within its limitations. However its very design can lead it to failure. It requires a certain amount of speed difference between both rear wheels to operate. Basically more slip than you would ever encounter going around a turn, but it will not lock at speeds above roughly 20-30mph. This it where it earned the name "gov-lock". It has a speed governor that operates off centrifugal force inside to govern locking.

When it locks, it locks hard. Imagine one tire sitting still, and suddenly being launched to a speed of 20-25mph. That takes a great deal of force and puts a lot of strain on internals. They have a tendency to break with no warning.

Page also has photos of one that has failed.

http://www.ar15.com/forums/t_1_134/1250761_g80_differential_...

⬐ bithush

I use this video quite often to show an example of one of the best educational videos I have ever seen. The language, presentation, use of graphics (impressive for the time) and demonstrations is just superb.

⬐ Yahivin

I like how they start ghost riding the whip at 8:45 https://www.youtube.com/watch?v=K4JhruinbWc#t=519

⬐ mxfh

Around the Corner (1937)

Producer: Handy (Jam) Organization ☞

Sponsor: Chevrolet Division, General Motors Corporation

Probably the source of this re-encode, with significantly less artifacts, on archive.org: https://archive.org/details/Aroundth1937

☞ Named after Jam Handy: https://en.wikipedia.org/wiki/Jam_Handy

⬐ spiritplumber

If you like videos like this, check out Retrotechtacular on Hackaday. They have a series on mechanical firing computers on navy ship that is nothing short of mech-eng porn, and I mean the classy kind.

⬐ rootbear

I watched that whole series a year ago and was fascinated. I believe it has been posted here before but it's worth repeating.

⬐ k2enemy

That was amazing, thanks. I found the integrator and multiplier especially simple and clever.

Here is a link to a youtube playlist: https://www.youtube.com/user/navyreviewer/videos?query=mecha...

⬐ reckoner13

My favorite: Wave Behavior from Bell Labs: https://www.youtube.com/watch?v=DovunOxlY1k

⬐ analog31

Excellent use of graphics, created in the age before computer graphics.

⬐ hughlomas

A World War 2 training video for evading flak cannon fire is one of the best examples of graphical information presentation that I've seen. https://www.youtube.com/watch?v=qP_-WUMi-nw

It features smoothly animated and highly functional designs as well as overlaying graphics on real footage to achieve a fashion of "augmented reality". The production quality is astounding and it is amazing to think that it was produced in the 40s. The entire video is an inspiring example of conveying information.

⬐ jonesdc

Thank you for posting this.

⬐ joshontheweb

That was really interesting. I never knew there was this kind of strategy behind flak evasion. Man, must have taken some stones to do a bomber mission. I knew an old timer that flew bombers in WW2 and he said towards the end of the war the germans were running out of metal and all sorts of things were used as flak. He said nuts and bolts were pretty common. He'd find them embedded inside the cabin after close flak fire. Pretty scary to think that your end might come from a washer.

⬐ DanBC

RAF Bomber Command had appalling rates of attrition through WWII.

http://en.m.wikipedia.org/wiki/RAF_Bomber_Command

The wiki article gives good explanation of how bombing developed during WWII - starting as a weapon to terrible to be used (based on poor quality data); with general agreements not to kill civilians; realising that bombers were hopelessly inaccurate; changing tactics to allow bombing of civillian populations, including the (to my mind) war crimes of fire bombing.

> Bomber Command crews also suffered an extremely high casualty rate: 55,573 killed out of a total of 125,000 aircrew (a 44.4% death rate), a further 8,403 were wounded in action and 9,838 became prisoners of war.

That's pretty much "toss a coin".

⬐ rahulmax

Wow! Amazing.

There's another video from 1949 about 'How a Watch Works' — http://www.youtube.com/watch?v=508-rmdY4jQ

⬐ draker

I had not seen this particular video but have seen the "How a manual transmission works" from the same series.

https://www.youtube.com/watch?v=aAWxZRuBXtw

⬐ JasuM

An interesting mechanism using differential gears, doubling the speed while only using gears of the same size:

http://507movements.com/mm_226.html

⬐ nopar8

The way the teaching was sequential really made it an understandable to a layman like myself.

⬐ petercooper

There's a chap who collects tons of videos like this on YouTube. He was mentioned on MetaFilter the other day: http://www.metafilter.com/143903/Do-you-like-vintage-trainin...

Or you can find his channel direct on https://www.youtube.com/user/webdev17/videos

⬐ blt

This is the best technical education video I've ever seen. If all information were available in such an easy to understand form, the world would be full of geniuses.

The level of effort is astounding. The "support" part holding the spokes looks cast. They couldn't have possibly cast that part specifically for this video... could they?

⬐ niels_olson

casting one-offs with a disposable form (wax, styrofoam) isn't particularly difficult or expensive. They use big basins full of super-fine sand: a great insulator and the grains are too tightly packed for the liquid metal to flow into the tiny spaces between them. We used to do it in high school shop class.

⬐ haphazardeous

Brilliant video. It's definitely a lot better to see the basic principles and evolution of those principles in action.

⬐ charlieok

I remember reading through David Macaulay's “The Way Things Work” as a kid, soaking up the illustrations until I understood each one. It was life-changing. However, I remember having trouble with one page in particular -- the one describing differential gears. Of course, video would probably have helped a lot :)

⬐ hsshah

I remember seeing this a while back and realizing I learned more from this video than I learned in class during my college course. Amazing production value. We should properly catalog such gems so that students and even professors can use these to teach (instead of attempting to reinvent the wheel)

⬐ VLM

I'd like to see a Torsen gearcase. Strange little things, they look like pepper grinders.

⬐ amenghra

I remember building lego cars which had a differential: http://groups.csail.mit.edu/drl/courses/cs54-2001s/images/le...

⬐ clebio

The actual explanation doesn't start until about 2 minutes in: https://www.youtube.com/watch?v=K4JhruinbWc#t=110

⬐ charlysisto

I was generally not bad at physics but I remember not getting my head around this one...

What a great lesson for decoupling systems. I wonder what's the software equivalent in design pattern land. The facade maybe ?

⬐ tapatio

I never really got my head around electricity and magnetism. That stuff is very abstract.

⬐ noblethrasher

Not sure about a corresponding design pattern, but the content neatly maps (no pun intended) to function composition.

⬐ leeoniya

some may also enjoy a 3d-printed triple gear

https://www.youtube.com/watch?v=I9IBQVHFeQs

⬐ wmeredith

Does this have any possible practical applications? Or is it just cool?

⬐ jonmrodriguez

Is it possible to create a "negative differential gear" that puts more torque into the wheel that is stuck? (in the hopes of forcing it unstuck)

⬐ birdmanjeremy

Yes. You are referring to a locking differential, of which there are several types. Some use clutch plates, and will work even if one wheel has no traction at all, others use more complex gearing and can transfer torque from one to another at some multiple (called a Torsen Differential) and cannot drive when one wheel is completely unloaded.

⬐ jonmrodriguez

Awesome, thank you!

⬐ franciscop

It is just too awkward that I learned how they work with the same video last year, still better than my University's current presentations

⬐ joeblau

Differential -- the most misused word in sports. The video is a great explanation about the automobile version.

⬐ sreejithr

I'd have loved it if these guys had made a video on fly wheels. Dying to know more about those.

⬐ gradstudent

@edferda: props for posting this; the pedagogy here is just terrific!

⬐ None

None

⬐ sisar

Any idea for what purpose was this video originally made?

⬐ smilefreak

I guessed some of the next steps, and considering I have the automobilic knowledge of the ancient greeks, that was pretty impressive.

An education in how to present to a lay audience.

⬐ mickcartwright

love the clarity, simplicity and enunciation

⬐ nikant

Great Video:)

⬐ spacefight

Best spent 8minutes today, thanks!

⬐ thebladerunner

Interesting

⬐ __database__

Amazing!

⬐ Animats

We know. I put a link to that video (to the Internet Archive, not YouTube) on Wikipedia years ago.

There's a whole series of Chevrolet films from the Jam Handy organization at the Internet Archive. "Take it Easy", "Spring Harmony" and "Shockproof" cover how auto suspensions work. "Facts on Friction", "Hydraulics" and "What stops them" explain brakes. "Head on" and "No Ghosts" - auto frames. "Water Boy" - cooling. "Free Air" - carburetor. There's more.

⬐ cipherzero

I had never seen this, so i appreciate the link. Is there any similar video for a limited slip differential?

⬐ function_seven

Here's a good start. Alter search query to taste.

https://archive.org/search.php?query=creator%3A%22Handy%20%2...

⬐ thebladerunner

Interesting

⬐ thebladerunner

Interesting

⬐ journeeman

Wow, that was a fantastic video. I could understand it easily only because they iteratively added complexity to the models. It's amazing how well they have made the tutorial for the layman.

Thanks a lot for sharing.

⬐ wickawic

If you liked that, you might like this similar video about how a mechanical watch works:

http://www.youtube.com/watch?feature=player_detailpage&v=508...

⬐ journeeman

Enjoyed watching it. Thanks. :-)

I always found this one video (http://youtu.be/K4JhruinbWc) on differentials enlightening.

⬐ mzs

Those old Handy organization films are incredible, here is my favorite but GM commissioned a lot of them.

http://www.youtube.com/watch?v=CCtJlgtZnBY

The US Army also has many very nice ones intended to introduce mechanics as well, there is one about power steering that is very good, but many more as well.

http://www.youtube.com/watch?v=AlpvyWAA8a0

⬐ agumonkey

Here's another one http://www.youtube.com/watch?v=mkQ2pXkYjRM : gears.

In case you're interested, here are two of the best video's I've seen describing how a watch works ( http://www.youtube.com/watch?v=OiCPu0SjEW4 ) and how a differential works ( http://www.youtube.com/watch?v=K4JhruinbWc&t=1m50s )

Don't let their old school-ness throw you off. They are both extremely well done and demonstrate in clear and simple language from first principles to finished object.

Full version (with rather long intro, but un-cropped ending): http://www.youtube.com/watch?v=K4JhruinbWc&NR=1

⬐ elblanco

What an amazingly excellent video.

⬐ regularfry

About the only thing that could have improved it would have been a Feynman voice-over.

⬐ InclinedPlane

This prompted me to search for Feynman videos on youtube. Sure enough, there are many. This will probably cut into my productive time the next several days.

⬐ elblanco

Feynman has a way of doing that. I'm about 6 years into a Tuvan Throat Singing Obsession because of him.

http://www.youtube.com/watch?v=DY1pcEtHI_w

Wait till about 20seconds in before you hear the most amazing thing in the history of music.

⬐ sern

And it's a promo produced for General Motors. If only today's advertisements were as informative and modest.

⬐ pkulak

This kind of planetary gear is used for a lot of other things too, like Toyota's hybrid system. It's really good for any system where you want to split power, but not torque. I've never heard it explained like this though. Really great video.

⬐ InclinedPlane

You'll notice though that a differential doesn't solve the problem of one of the drive wheels not having any traction (mentioned early in the video as a problem of one wheel drive cars). In that case the differential will spin the wheel with no traction while not sending any power to the wheel that does have traction (in the same manner as it would if you happened to be taking a very sharp turn that left one of the wheels nearly stationary). An excellent video otherwise, but I thought that was an odd aspect.

⬐ JshWright

I'm not much of a car person, but did limited slip differentials exist at the time this video was made? To me it would seem more odd if an advertisement explained the mechanics behind something that the product it was advertising couldn't do...

⬐ InclinedPlane

Limited slip differentials were apparently invented in the 1930s but were relatively exotic (reserved for race cars) until about the 50s. I suspect the makers of the film were just a little confused and didn't fully appreciate the problem.

Also, I can't resist posting a link to this video of a working differential built using legos: http://www.youtube.com/watch?v=zOijFK7uh6U

⬐ herdrick

But the torque applied to both wheels will always be equal in theory, so the spinning only happens because of the 'dynamic friction is often less than static friction' factor. This does mostly solve the problem.

⬐ lutorm

The torque will be equal but will be equal to that of the spinning wheel, which does not help much.

And it's worse than dynamic vs static friction, in cases where you really need it it's likely the wheels are on different surfaces (one in snow, the other on pavement, for example) and then both wheels will have the torque equivalent of being on snow...

⬐ Deestan

> In that case the differential will spin the wheel with no traction while not sending any power to the wheel that does have traction

Boy do I ever get reminded of this every winter. It's a shame that cars that have the option to lock the differential gear are a lot more expensive.

⬐ mhb

And for more on limited slip differential:

http://en.wikipedia.org/wiki/Limited_slip_differential

⬐ Deestan

Thanks! Now I know what to look for. It seems the "electronic limited slip differential system" is what I want, as my main trouble is getting out of icy parking spots.

⬐ rbranson

2006 (and later) Honda Civic Si's come with a limited slip differential, and are fairly affordable, from both a purchase and a maintenance perspective. While the LSD is mostly for traction under hard cornering, as accelerating out of a corner is a huge weak point of front-wheel-drive, it does work to increase traction in wintry or wet weather by distributing torque over both wheels.

⬐ eitally

Not necessarily (but availability probably depends where in the world you are). You can get a Subaru Impreza with a locking center diff.

⬐ dtegart

A limited slip differential solves most of this problem, and you don't have to worry about unlocking the diff when you are on dry road. (having a locked diff means the tyres will have to slip over the road when turning. On a dry road they won't slip as much and this can cause significant damage to various components)

⬐ ajross

Bah, humbug. Lazy young'uns. When I was growing up, we didn't have no youtube. We had to learn differential gears by actually assembling one in a RC car model kit.

Obligatory irony: it was this one: http://www.youtube.com/watch?v=7OCeKMHzEbQ

⬐ Splines

Do modern cars no longer lower the drive shaft as in this video? I haven't really seen a sedan with a flat floor in the rear for some time (ever, in my lifetime anyway). Is it just that the floors have been lowered so much that you can't really lower the drive shaft any further?

⬐ jcoby

modern cars are much lower than cars from the 30s. the driveshaft pretty much has to be recessed into the body to give any useful ground clearance and to protect the drive shaft from speed bumps and road hazards.

⬐ dmarble

Did they seriously use Tinkertoys for that model? Sure looks like it! Awesome explanation.

Reminds me of what used to be my favorite website to kill time but still learn something: http://howstuffworks.com

⬐ glhaynes

Fake. Check out the obvious mouse pointer UI being used at 07:28!

⬐ glhaynes

I guess I should've used a smiley. :)

⬐ None

None

⬐ gchpaco

The part about this that I find the most interesting is the way it explains how a differential can be thought up, rather than presenting it as some bolt from the blue.

⬐ movix

Interesting difference in the attention spans of the 1930's to now. 1:50 in and still not a word of commentary on what this is about. How many people on HN sat through this whole video?

"Recent studies show that Internet users spend as little as 50 milliseconds scanning a website before deciding whether it is of value to them or not." Source: http://www.messagingtimes.com/blog/2006/03/15/microcontent-m...

⬐ thwarted

Heh, true. I had to skip ahead. That being said, this massive intro was more entertaining than most intros you find on Youtube, but how long can anyone be expected to watch the same three Motorcycle stunts/tricks? What stood out to me was the short text scroll at the beginning. I was thinking "wow, people even put slow, useless text at the front of their videos 50 years ago, it's not just a Youtube phenomenon".

Nevertheless, an interesting video. I learned something; I've actually been wondering exactly how that worked for a while (classic hacker attribute: enough to think about it and perhaps determine it on my own, but not curious enough to just look it up).