Searching for any lead on realistic cord mechanics

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Discussion Overview

The discussion revolves around the mechanics of a multishafted cord system used for force transfer, focusing on its elastic properties, friction in pulleys, and the implications of mass. Participants seek research directions, models, and relevant literature to better understand the complexities involved in this topic.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant, Erandom, describes the challenges of modeling a cord with elastic properties and seeks resources on force transfer in systems like cranes, mentioning the Capstan Equation as a starting point.
  • Another participant suggests exploring cable and cordage resources as a potential avenue for information.
  • A link to a paper is provided, which one participant acknowledges as helpful for their research.
  • A participant emphasizes the importance of maintaining tension in cords to ensure proper force transmission and discusses the implications of impedance mismatches at pulleys.
  • Erandom expresses uncertainty about calculating frequencies related to resonance in their system due to unknown friction coefficients and stiffnesses, considering empirical methods for investigation.
  • Another participant shares insights on control cables in aircraft, suggesting a closed-loop arrangement to mitigate actuator delay and improve oscillation frequency, along with a reference to a relevant paper on cable-driven robots.

Areas of Agreement / Disagreement

Participants express various viewpoints on the mechanics of cord systems, with no clear consensus on the best approach or model. There are differing opinions on the importance of tension and resonance, and the discussion remains unresolved regarding the optimal methods for analysis and experimentation.

Contextual Notes

Participants note limitations in their understanding due to unknown variables such as friction coefficients and stiffnesses, which affect their ability to model the system accurately. The discussion highlights the complexity of the mechanics involved and the need for empirical investigation.

Erandom
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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
 
Engineering news on Phys.org
Cable and cordage, rope/cable lays may get you a toehold into what you're after.
 
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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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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,
 
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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