Finding the spring constant of a torsion spring.

AI Thread Summary
To find the spring constant of a nylon rope acting as a torsion spring, the user needs to determine the torsional coefficient (kappa) based on the rope's dimensions and the angle of twist. The diameter of the rope bundle is approximately 6 cm, and the rope has been twisted 1080 degrees (3 full revolutions). The user seeks to calculate the force exerted by an arm fixed in the middle of the spring when pulled back 50 degrees with a length of 50 cm. The relationship between torque, angle, and the spring constant is given by the equation Torque = -kappa * theta. Understanding these principles will help in calculating both the spring constant and the forces involved when the arm returns to equilibrium.
Silvershield
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Hi,

How would I go about finding the spring constant of a bundle of nylon rope acting as a torsion spring?

I know the length. I don't know the width of the bundle. When twisted I wanted roughly 6cm diameter (is that a wrong method)?

I ll be twisting it by 1080 degrees.


When twisted as above ^ -

how can I calculate how much force/energy it will project if an arm in the middle of the torsion spring is pulled against it by a certain length/angle.

Im guessing that the longer the arm, the more it can pull back.

Like a ballista.

Thank you.
 
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I'm sorry, could you clarify your question? But here are some stuff I know about torsion.


Torque = -\kappa\theta
Where Kappa is the torsional coefficient and theta the angle rotated.

Period = 2\pi\sqrt{I/\kappa}
 
Yes, the question is a bit over the place.

Im trying to find the spring constant (k) of a bundle of nylon-6 rope.

The total diameter of the rope is 6cm roughly.

I've twisted the rope bundle 3 full revolutions and have fixed it at equilibrium.

The length of this rope bundle spring is 36cm

What is the working out/steps/equation to find the spring constant?

Furthermore, If I fix an arm in the middle of the spring, I wish to find the force needed to pull back 50 degrees (length 50cm of arm), and the forces the arm will project when it returns to equilibrium.

I know how to find the spring constant of a metal spring coil, however.
k = ( E*d ^3) / (8 * D^4 * n)
n = number of coils
d= wire diameter, D = diameter of spring, E = young's modulus
 
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