
How a differential gear works (1937) [video] - edferda
https://www.youtube.com/watch?v=K4JhruinbWc
======
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...](http://www.youtube.com/watch?feature=player_detailpage&v=508-rmdY4jQ#t=315)

~~~
journeeman
Enjoyed watching it. Thanks. :-)

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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](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](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.

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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.

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Yahivin
I like how they start ghost riding the whip at 8:45
[https://www.youtube.com/watch?v=K4JhruinbWc#t=519](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](https://archive.org/details/Aroundth1937)

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

~~~
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...](https://www.youtube.com/user/navyreviewer/videos?query=mechanical+computer)

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reckoner13
My favorite: Wave Behavior from Bell Labs:
[https://www.youtube.com/watch?v=DovunOxlY1k](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](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.

~~~
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](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](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](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](http://507movements.com/mm_226.html)

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nopar8
The way the teaching was sequential really made it an understandable to a
layman like myself.

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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...](http://www.metafilter.com/143903/Do-you-like-
vintage-training-educational-fims-Meet-Jeff-Quitney)

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

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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.

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amenghra
I remember building lego cars which had a differential:
[http://groups.csail.mit.edu/drl/courses/cs54-2001s/images/le...](http://groups.csail.mit.edu/drl/courses/cs54-2001s/images/legodiff.jpg)

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

~~~
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](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.

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

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sisar
Any idea for what purpose was this video originally made?

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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.

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mickcartwright
love the clarity, simplicity and enunciation

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nikant
Great Video:)

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spacefight
Best spent 8minutes today, thanks!

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thebladerunner
Interesting

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__database__
Amazing!

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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...](https://archive.org/search.php?query=creator%3A%22Handy%20%28Jam%29%20Organization%22%20suspension)

