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Hi all,

I am curious about if there is limitation about how many degree could the arm of an torsion spring turned? Is there any limitations? Also, it would be great to read if there is any information about it.

Thanks in advance.
Quote:how many degree could the arm of an torsion spring turned?
The design of the torsion frame limits the angle of rotation. In Marsden's version of the euthytone (i.e. the arrow-shooting catapult), the arms travelled through 35 degrees. In his version of the palintone (i.e. the stone-projecting ballista, subsequently adapted for shooting arrows), they travelled through 50 degrees. Configuring the palintone as an "inswinger" increases the angle dramatically to around 90 degrees.
So is it possible increase the limit if some other type of frame used? My question is more about sinew fibers. Is there any deformation after certain degree?
Quote:So is it possible increase the limit if some other type of frame used? My question is more about sinew fibers. Is there any deformation after certain degree?

Have you checked out this article: The inswinging theory?
Yes, I read it for some times ago. Nice article about how in-swinging arms provide more rotation thus enables springs store more energy thus producing more powerful machine. In that article, in-swinging arms could be turned minimum 103 degree. My question is if this could go further without constrained by material limits of sinew spring.

I am asking this because in one of the Leonardo da Vinci's springald design, there are four arms in one spring. In my opinion, the shooting string of springald is fitted to outer arms and other arms were used for support the "bow" string. This configuration could provide almost 360 degree of turn, making machine even more powerful. Yet, I am not sure if sinew cords could handle this.

[Image: Leo_springald.jpg]
Quote:My question is more about sinew fibers. Is there any deformation after certain degree?
The problem here is that no-one (afaik) has ever published any research on the manufacture and testing of sinew cord/rope. According to Michael Lewis (who has researched into ancient engineering generally), Digby Stevenson managed to make some sinew rope, but never published any details.
Quote:According to Michael Lewis
Alan Wilkins has mentioned it before he did (JRMES 6, 1995, p. 44; JRMES 11, 2000, p. 99).


Quote:Digby Stevenson managed to make some sinew rope, but never published any details.
This is not so. He gives a short description of the process in the article "The manufacture of sinew rope" (Journal of the Society of Archer-Antiquaries 40, 1997, p. 16). The process is very similar to making of sinew bowstring by modern traditional bowmakers (the video can be easily found on youtube). One should also consult his BA dissertation (which, unfortunately, is not available to me): "Heron's cheiroballistra, with an appendix on the manufacture of sinew rope", UCL, 1995.

P.S. J.E. Gordon in his famous book "Structures or why things don’t fall down" specifies the working deformation of sinew as 8%.
Thanks for information. Yet all those works are rather theoretical and has no meaningful contribution. I don't think there is any way to calculate or predict the possible deformation of sinew springs turned to a certain degree. It seems this question can only be answered by careful experimentation in a practical way.