Searching for any lead on realistic cord mechanics

  • #1
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Hi all,


I'm a physicist, and I'm now trying to understand and model a problem with a multishafted cord, being pulled from one side in order to transfer force. The cord has its own elastic properties (elongation, bending etc.), it goes through several pulleys with friction, and most likely its mass is not negligible.

Point being, from the physics perspective, everything I've neglected in my BSc, came back for revenge.


Can anyone point me in a direction of research and models on this topic?

I tried looking for articles and calculations for force transfer on cranes (assuming that in long ropes the elastics are important). I searched for equations in the field, but only found the Capstan Equation. I have found very little helpful materials until this moment.

Any lead, book, suggestion or even subject name in English will be very helpful at this point.


Thank you very much in advance,

Erandom
 

Answers and Replies

  • #2
Bystander
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Cable and cordage, rope/cable lays may get you a toehold into what you're after.
 
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  • #5
Baluncore
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I should remind you of the necessity of keeping tension in your cords to maintain the speed of sound. Cords break when the ends of the system move independently and the speed of sound in the cable permits transmission line characteristics to come into play.

I have not read the references posted, but control wire and cord systems are transmission lines with impedance mismatches at the pulleys. To transfer energy without reflection requires matched impedances. Local reflection of energy has been used to cut thread when stitching agricultural bags.

Resonance systems should be avoided as the stored energy is either destructive or rapidly lost.
 
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  • #6
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Thank you for the extra input. My system is not in full tension (at least when I start pulling). It's interesting whether one can exert force through a semi-rigid cord while there are still DOFs that can be streched and get to higher tension.
Your comment about resonance is very important, but I find it very hard to calculate the frequencies when I don't know the frictions coefficients or the stiffnesses. Maybe I should just try to find this empirically.

Thanks again,
 
  • #7
Baluncore
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Control cables in aircraft are/were arranged in a closed loop as a differential pair. They are adjusted and pre-tensioned so as to reduce actuator delay and raise the frequency of oscillation.You might consider using two cables in a similar closed loop.

Google 'analysis of control cables' and amongst other offerings you will find;
“Dynamic Analysis And Control Of Cable Driven Robots With Elastic Cables”.
http://www.tcsme.org/Papers/Vol35/Vol35No4Paper6.pdf
 

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