This image [1] explains the mechanism better. Next, imagine the cord is in fact the shaft of another pair of wheels.<p>[1]<a href="http://drgoulu.com/wp-content/uploads/HLIC/849e60a7d99c30c2af0480c7c5b49d71.jpg" rel="nofollow">http://drgoulu.com/wp-content/uploads/HLIC/849e60a7d99c30c2a...</a>
Richard Feynman mentions these in <i>Surely You're Joking, Mr. Feynman!</i>:<p>> 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?”<p>> “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!<p>> 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.
This was a kid's toy when I was young. Came in Remco's "Sneaky Pete's Magic Show"<p>Here's a video demoing it.<p><a href="http://www.youtube.com/watch?v=-4MEvkR0sHw" rel="nofollow">http://www.youtube.com/watch?v=-4MEvkR0sHw</a>
Here, I just made one: <a href="http://www.thingiverse.com/thing:193022" rel="nofollow">http://www.thingiverse.com/thing:193022</a><p>Yes, it rotates and passes shafts successfully :)<p>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 ;)<p>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.<p>[1] <a href="http://www.thingiverse.com/thing:126794" rel="nofollow">http://www.thingiverse.com/thing:126794</a>
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.<p>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.
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 <a href="https://en.wikipedia.org/wiki/Topoisomerase_II" rel="nofollow">https://en.wikipedia.org/wiki/Topoisomerase_II</a>
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 -> <a href="http://books.google.com/books/about/The_Planiverse.html?id=wIzwyzHSrL4C" rel="nofollow">http://books.google.com/books/about/The_Planiverse.html?id=w...</a>
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.
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)<p>My answers to some of your questions:<p>Yes, my own images are free ( <a href="https://en.wikipedia.org/wiki/File:Shaftpasser1.jpg" rel="nofollow">https://en.wikipedia.org/wiki/File:Shaftpasser1.jpg</a> and <a href="https://en.wikipedia.org/wiki/File:Shaftpasser2.jpg" rel="nofollow">https://en.wikipedia.org/wiki/File:Shaftpasser2.jpg</a> ) . The scan from the mine cable was sent to me by email but I don't know its exact reference and status<p>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 ;-)<p>Congrats to ambrop7 for the printable model !
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..<p>..though i get the implication of design vs engineering<p>[1] <a href="http://upload.wikimedia.org/wikipedia/commons/thumb/1/16/Ball_Bearing2.jpg/560px-Ball_Bearing2.jpg" rel="nofollow">http://upload.wikimedia.org/wikipedia/commons/thumb/1/16/Bal...</a> )
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?