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I need a shaft that can be stretched along its length while also being resistant to torque enough to be a functional shaft (see pictures). I have a rotating sphere within another rotating sphere, hence the use of universal joints. But due to the universal joints I can't use a shaft that is long enough to slide up and down. You can see in my images where there's a shaft missing. I don't know of the existence of any rubber that is sturdy enough to withstand the torque applied while also being stretchy enough to span that gap. Perhaps there's other ways to achieve what I am trying to achieve without the use of universal joints (I am open to suggestions).

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Edit:

Perhaps I could 3D print a sort of origami shaft that unfolds?

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This is getting to be a bit ridiculous lol what I'm trying to make shouldn't be rocket science

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  • $\begingroup$ Search for spline shafts. $\endgroup$ – Eric S Oct 12 '19 at 20:45
  • $\begingroup$ I see how a spline shaft would be useful for sliding up and down but there just isn't any room in the universal joints for a rigid shaft. If I put a spline shaft it would intersect with the mechanism inside the universal gears when the joint is in its straight position $\endgroup$ – 小奥利奥 Oct 12 '19 at 21:01
  • $\begingroup$ Use a lemon shaft... $\endgroup$ – Solar Mike Oct 12 '19 at 21:14
  • $\begingroup$ @SolarMike I looked up lemon shaft and it seems to be a variation of a drive shaft (?) which is honestly exactly what I needed, the wikipedia page for drive shafts even shows them being used with universal joints (which is why I need them) in conjunction with a spline (which is what the other guy suggested), and you don't want to know how far I got with my origami shaft (lol) someone post an answer so I can accept it $\endgroup$ – 小奥利奥 Oct 12 '19 at 21:24
  • $\begingroup$ If you've not yet researched constant velocity joints, you may want to consider the effect of a universal joint in comparison. A u-joint has varying rotational speed depending on the angle of deflection, which is periodic to the rpm, while a constant velocity joint has uniform rotation speed. There are wide variations for CV joints as well as with U-joints, some are small enough for radio control car models, others are huge truck size. $\endgroup$ – fred_dot_u Oct 13 '19 at 0:53
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There are sliding shafts used for agricultural machinery commonly called a "lemon shaft" and they are available in several sizes.

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  • $\begingroup$ They are also available in small sizes for radio controlled rock crawlers. They are used as the main drive shaft to accomodate large movement of the suspension system for the front and rear differentials. $\endgroup$ – DKNguyen Oct 14 '19 at 15:19

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