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Comment by GauntletWizard | Hacker News Reader

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.

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Yeah, I think in practice, as drawn, the red wheels would simply jam up. And if they don't, the outer rim of the big wheel would not hold its place relative to the inner part. I dont see how the outer rim could be solid enough, relative to the inner hub, to do any useful job. The whole thing just breaks.

http://www.drgoulu.com/2005/12/29/eviteur-daxe/

The mine application seems to be a subset version. If that is the best example any one has of this design in practice it suggests that its not possible to build a working version of the whole thing. A mechanically weak proof of concept might be possible, but a solid use-able version seems to me to be impossible.

Might work if the outer rim is supported or guided on some way. I still think loading is a problem though.

I love to see some one try to build it....

I don't know if tightness has anything to do with it. As long as the passer cannot escape its enclosure, it would pass power, because it is being dragged by the inner spoke. The real problem is the amount of force being placed on the passer and the probably impact of routinely passing the shaft through at high velocities.

This is a really good analysis – I thought the design was simple at first, but now even the cable-passing-cable version linked in the wikipedia page looks liable to jam as teeth pass in and out of the top channel.

For something like this to even have a chance, it would probably need many more, thinner teeth than these diagrams illustrate.

EDIT: @analogwintermut I think this addresses your question.

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?

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.

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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