
Shaft passer - earthrise
https://en.wikipedia.org/wiki/Shaft_passer
======
chm
This image [1] explains the mechanism better. Next, imagine the cord is in
fact the shaft of another pair of wheels.

[1][http://drgoulu.com/wp-
content/uploads/HLIC/849e60a7d99c30c2a...](http://drgoulu.com/wp-
content/uploads/HLIC/849e60a7d99c30c2af0480c7c5b49d71.jpg)

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asdfs
I wonder if that image is in public domain. Might be nice to add to the page.

~~~
mvleming
Is it? I don't know how to look for whether a photo is in the public domain,
but I did just Google with the image.
[https://encrypted.google.com/search?tbs=sbi:AMhZZisuyc26lmhJ...](https://encrypted.google.com/search?tbs=sbi:AMhZZisuyc26lmhJR0LVZESx28a2CpeDWhtXNlFm3m0MD9lQoxeCc92BHOvx1dWvevOt8OKHABd_19Ga0q1CX2MatkZ0Mplq3HEf8-l0YkMFJdX5_1-weidZDktV133A7hlWD1GxN0o28RPcKst7y0e6hauoDH25JZHc-q6X4gKgDud7Vnngf0rDsMcJGAUfDavONeXPdVEbr63ho0IrqY64pegnq5U5704sPTh_1FAKIVbJ4AOuhdHjtuuvPlXg8OtkRSgSfoc4U6CJa7dR2YQBHkGAzbrJ16sQs-
voqerWFdfuEi-T5bUjAkvQGl46qx3Biv21_1L4wQQqP9zn0UIFDr5hOIFPFet5dPO57-qdvbFyx0Z7yC62qz6tBeon-
Ivvkl6eEIKSnINpWWOpbsscBNwD7Ff5lZuQ64FkVVCPL_1Ru1bnn83nTvt8DwjfnWnqWmLfVy5_1LNKOZp97rhxf-8sGbYD0q5C00AIDUgZXp8yS27hPYtgm1I_1rcBplIMHu6KoZAtcPRxw6EbtgMvU3kFIKJDO8qvoEMiw8SXlWp6QusCM8N8y2wCEO2T88lWienzL0uhFlFrs2s7RbJwcWo2rnEBUOe9-6zBPM4ppDtyOQ-1L9VJvJP8gIDYHXRu2_1AyVjShwl1dw39yNRd3L7dL7tOzCxt550EewK4mfAwSxu23C-Cwjnb5R5CzWQtkOCXUWkbx8MX5m5L2rUyj6mv1Jz0jV7u7M1-FiWhAFddPQhFHOKoW2NjLQMZIKGuRMpFoEH_1pqo-5AETU4VzYF84w3w9ADzHzPw7uTaqHdw6cEIdpSnhD5mNXnZu7hvCxO8Vk26Jhzn4g7T2DlF-D72LRcXL0Ez03lVK0eNK-
aDJBjZDyIhV-
GJkwmEP8sPgBeh2Q_1Z53QM0-BChrXowF_1a5PDBi79IDzG6KajebXYvpw8-d3qJq_1jB6Fl73PkTGmTtpS6KzUSIHLwGL0iYBP1gggqk9AhwvE21NSB0DPqfaU-
apdzOT5KDOrLC3xrQ7MiNxUiZFv-b6UsxauD0ifJqelDjxlB0R15CBH6p-1SBg927vnNaOjjqK9ngxPE2bcl-1_1yiTydNwtQKRre6BgVaqCI1GL2GpxmbfeD0U3MY8ZtIkyuOzf4JBCHAct7ydy9md4zlCg6yLVuY6UmjyRmi2gqYodC2twuiQTvKJOEohaIpRkOnnLwL3XQM-
gjnBdNIDn2lV2gbRYC2Yao_11nnlv1LTCGqUu2gx97Z_1aqe6_1cro-
OoOCOYiMgt659E_1WXCaf1q6qZCegjP0VTIsC55iFmxfCK3xcMz_1Ax1D3zAxNtKTia5u8FloYAJs)

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Rangi42
Richard Feynman mentions these in _Surely You 're Joking, Mr. Feynman!_:

> One mechanical engineer at Frankfort was always trying to design things and
> could never get everything right. One time he designed a box full of gears,
> one of which was a big, eight-inch-diameter gear wheel that had six spokes.
> The fella says excitedly “Well, boss, how is it? How is it?”

> “Just fine!” the boss replies. “All you have to do is specify a shaft passer
> on each of the spokes, so the gear wheel can turn!” The guy had designed a
> shaft that went right between the spokes!

> The boss went on to tell us that there was such a thing as a shaft passer (I
> thought he must have been joking). It was invented by the Germans during the
> war to keep the British minesweepers from catching the cables that held the
> German mines floating under water at a certain depth. With these shaft
> passers, the German cables could allow the British cables to pass through as
> if they were going through a revolving door. So it was possible to put shaft
> passers on all the spokes, but the boss didn’t mean that the machinists
> should go to all that trouble; the guy should instead just redesign it and
> put the shaft somewhere else.

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MaggieL
This was a kid's toy when I was young. Came in Remco's "Sneaky Pete's Magic
Show"

Here's a video demoing it.

[http://www.youtube.com/watch?v=-4MEvkR0sHw](http://www.youtube.com/watch?v=-4MEvkR0sHw)

~~~
pohl
I wonder if that is the genesis of the character named Stinky Pete in Toy
Story 2.

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ambrop7
Here, I just made one:
[http://www.thingiverse.com/thing:193022](http://www.thingiverse.com/thing:193022)

Yes, it rotates and passes shafts successfully :)

Based on this model[1] with some modifications for printability. I've printed
it in 6 parts and glued it together. It's barely holding though, because
apparently super glue is not the best way to bond ABS ;)

EDIT: I just figured out that to use it as a shaft passer inside a wheel just
like on the Wikipedia article, the rotor would need some plastic removed so
that the shaft can get through without having to move up and down.

[1]
[http://www.thingiverse.com/thing:126794](http://www.thingiverse.com/thing:126794)

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k1w1
It is strange that the wikipedia article describes the shaft passer as
hypothetical. They are widely used in yachting harnesses - it allows your
safety harness to be connected to the life-lines and can roll over the
stanchions as you walk past them.

Anyone who has done the bridge climb over Syndey Harbour Bridge has used one
too. Unfortunately I couldn't find a good photo of the harness and connector.

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arthuredelstein
A similar trick is done by Type II topoisomerases, which are molecular
machines found in just about every living cell. Type II topoisomerases pass
one piece of DNA through another. See
[https://en.wikipedia.org/wiki/Topoisomerase_II](https://en.wikipedia.org/wiki/Topoisomerase_II)

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kyberias
Well, in fact the topoisomerase CUTS the second DNA and ligates it afterwards,
so it is obvious it can pass through. I don't think it's similar at all.

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noAlchemy
Fun fact about Type II topoisomerase: even though it only has local
information (the area where it acts) it manages to move in the correct
direction (lower unknotting number) about 90% of the time. AFAIK, no-one knows
how.

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drhodes
This is similar to how "zipper organs" work in AK Dewdney's The Planiverse,
they keep 2D creatures from being separated by their digestive system. The
passage that covers this concept is on page 44 which is unfortunately out of
the range allowed by the publisher ->
[http://books.google.com/books/about/The_Planiverse.html?id=w...](http://books.google.com/books/about/The_Planiverse.html?id=wIzwyzHSrL4C)

~~~
StavrosK
Eeh, amoebas can already do it in two dimensions without a complicated system
of gears that would mean they're two joined organisms anyway.

~~~
mbq
Amoebae have a very complex 3D structure; check out some SEM images, like
[http://www.sciencephoto.com/search?subtype=keywords&searchst...](http://www.sciencephoto.com/search?subtype=keywords&searchstring=amoeba+SEM)
or
[http://www.photomacrography.net/forum/viewtopic.php?t=21719](http://www.photomacrography.net/forum/viewtopic.php?t=21719)
. Moreover, most of their molecular machines require third dimension to work.

~~~
StavrosK
Sure, but if we're assuming there's life in two dimensions, the amoeba's
digestive system is much simpler than zipper organs.

~~~
mbq
It seems so on a first glance, but if you think about how this 2D phagocyte
can be formed (especially on a macroscopic scale) and how would it interact
with other structures it becomes much less obvious.

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wazoox
IIRC Hero of Alexandria made a similar device 20 centuries ago: a horse statue
that could had its head cut with a sword, without it falling down, with a set
of gears that let the sword pass through the neck of the statue without
letting the head go.

~~~
taspeotis

        head cut ... without letting ... go.
    

My mind works in mysterious ways. First thing I thought of [1].

[1] [http://www.bash.org/?488793](http://www.bash.org/?488793)

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NDizzle
Just think. You could really disrupt the 3 post curtain industry with a
passable middle post!

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rwinn
Someone with a 3D printer should try printing that model, looks like it could
work.

~~~
scott_karana
Likewise someone with a CNC machine, or woodworking tools, or stone chisels...

~~~
StavrosK
You mean you can create random stuff without 3D printers?!

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gcr
Honestly, I don't get the joke here. This looks like an interesting way of
solving the problem. What am I missing?

~~~
GauntletWizard
It looks like it should work, but the tolerances and tensions required make it
unlikely to ever actually work. For the model in the article to work, the
inner gears (in red) need to be A) Loose enough that the blue shaft can pass
between them B) tight enough to pass power from the interior of the wheel to
the exterior. This is improbable, and, while the solution seems sound, it's
never been shown to work; It maintains mythical status.

~~~
anologwintermut
So what happens when it's just used to pass through a cable(i.e. how it's
mentioned by Feynman)and not transfer power?

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myhf
In that situation the cable needs to be strong along its length but allow
passing through orthogonally. Whereas a gear would need to be both strong and
weak on the same axis.

~~~
darkmighty
I agree the _implementation_ isn't sound, but there's nothing wrong with the
_concept_ of a shaft passer.

As an example of why it is conceptually feasible, remember that you could
computationally (or mechanically) determine when a shaft is closing in and
open a gap in that particular support at the right time, maintaining ability
to pass torque through all other supports.

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Goulu
Thank you guys for discussing my work. You created a huge traffic peak on my
blog! I had to search a bit to find where it did come from as HN's links
apparently aren't tracked by WordPress statistics (rel="nofollow" I guess)

My answers to some of your questions:

Yes, my own images are free (
[https://en.wikipedia.org/wiki/File:Shaftpasser1.jpg](https://en.wikipedia.org/wiki/File:Shaftpasser1.jpg)
and
[https://en.wikipedia.org/wiki/File:Shaftpasser2.jpg](https://en.wikipedia.org/wiki/File:Shaftpasser2.jpg)
) . The scan from the mine cable was sent to me by email but I don't know its
exact reference and status

Clearly the wheel would be extremely difficult to produce and to operate,
especially if torque has to be transmitted. I intended to model a version with
the german cable design, i.e. one of the half-spoke attached to the star wheel
axle, but I leave this to the most fanatic of you ;-)

Congrats to ambrop7 for the printable model !

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cam_l
surely this would be technically feasible with a mechanism similar to a
bearing [1] but with teeth on the inner and outer and cogs in place of the
bearings (through which the shaft would pass)? the difficulty of course would
be to tune the teeth so the outer turns at the same rpm as the inner..

..though i get the implication of design vs engineering

[1]
[http://upload.wikimedia.org/wikipedia/commons/thumb/1/16/Bal...](http://upload.wikimedia.org/wikipedia/commons/thumb/1/16/Ball_Bearing2.jpg/560px-
Ball_Bearing2.jpg) )

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Ellipsis753
It seems to say that these were never used and then says that they were used
in the world wars? I was under the impression that they had indeed been used
successfully for mines. Is this not the case?

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ars_technician
I think it's saying that they haven't been used on all of the spokes on a
wheel.

They were used on the mines.
[http://drgoulu.files.wordpress.com/2007/03/minesweep.jpg](http://drgoulu.files.wordpress.com/2007/03/minesweep.jpg)

~~~
jackgavigan
I turned into doge for a moment when I looked at that image: "Wow. So simple.
Very elegant. Such genius."

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junto
Ah, the old sky hooks and tartan paint jokes.

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cfontes
I bite it, enlighten me...

~~~
ars_technician
[http://drgoulu.files.wordpress.com/2007/03/minesweep.jpg](http://drgoulu.files.wordpress.com/2007/03/minesweep.jpg)

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hotshotgg
definitely nice

