Winch rope force to pull back a folding canopy

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Discussion Overview

The discussion centers around determining the force required on a rope to pull back two hinged leaf panels that form a folding roof, utilizing a winch mechanism. Participants explore the mechanics involved, including the angles of the panels and the weight of the panels, while considering various approaches to calculate the necessary tension in the rope.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant raises the initial question about the force needed to pull back the panels, noting the weight of each panel and the angles involved.
  • Another participant questions the diagram's representation of the pivot point, suggesting that forces should be horizontal due to the nature of the pin connection.
  • A different viewpoint suggests that vertical reactions at the pivot point exist due to the weight of the panels, likening the setup to a toggle clamp mechanism.
  • One participant calculates the maximum tension in the rope at 5 degrees, arriving at a value of approximately 8967 newtons based on the weight distribution of the panels.
  • Another participant references an external source regarding toggle joints, indicating a tension of 457 kg at 5 degrees, and provides a formula to calculate tension based on moments about the pivot point.
  • There is a challenge to the assertion of vertical forces at the pivot, with a participant arguing that a toggle joint cannot support such forces and that any vertical force would compress the leaf members instead.
  • Further calculations are presented, with one participant arriving at a tension of approximately 4483.2 N using a different approach to the problem.
  • Questions arise regarding the unit conversion of tension from kg to kN, indicating a need for clarification on units used in the calculations.

Areas of Agreement / Disagreement

Participants express differing views on the forces acting at the pivot point and the calculations for tension in the rope. There is no consensus on the correct approach or final tension value, with multiple competing calculations and interpretations presented.

Contextual Notes

Participants rely on various assumptions regarding the mechanics of the toggle joint and the distribution of forces, which may affect the calculations. The discussion includes unresolved mathematical steps and differing interpretations of the physical setup.

1988ajk
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Hi all....

Struggling a little to determine the force required on the rope to pull 2x hinged leaf panels back. the leaf panels form a folding roof that will be opened/closed by a winch.

Each link weighs around 80Kg. theta starts around 5 degrees from horizontal and ends around 75 degrees from horizontal.

Thanks.

Screenshot 2025-12-19 131214.webp
 
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1988ajk said:
Struggling
I see your diagram with the top pivot point between L1 an L2 as having only pin connection.
Should not then the forces on the pin and sleeve be completely horizontal, much like a frictionless roller on a vertical wall.
 
There will be vertical reactions at the top pivot point due to the masses (mg) of each leaf. We are assuming this works similar to a toggle clamp mechanism. However, I am sure there are other methods of summing the forces to find the horizontal load at the rope.
 
Maximum tension will be at 5°. Half of the mass of each leaf rests on the ground, the other half at the top pivot, making 80 kg total at the top.
Tan(5°) = 80 kg / tension kg
Tension in rope; t = 80 / tan(5°) = 915 kg.
Tensional force in rope = 9.8 * 915 kg = 8967. newton.
 
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1988ajk said:
There will be vertical reactions at the top pivot point due to the masses (mg) of each leaf
No there will not be.
A toggle joint cannot support vertical forces transmitted through the joint.
Any vertical force put at the location of the joint instead results in compression of the leaf members.

This
256bits said:
I see your diagram with the top pivot point between L1 an L2 as having only pin connection.
Should not then the forces on the pin and sleeve be completely horizontal, much like a frictionless roller on a vertical wall.
this
Baluncore said:
Maximum tension will be at 5°. Half of the mass of each leaf rests on the ground, the other half at the top pivot, making 80 kg total at the top.
Tan(5°) = 80 kg / tension kg
Tension in rope; t = 80 / tan(5°) = 915 kg.
Tensional force in rope = 9.8 * 915 kg = 8967. newton.
and this
Lnewqban said:
are all the same thing.
 
It is important to pick the correct P when using the formula for toggle joint:

The answer from engineering toolbox : 457 kg tension at 5°.

1766354918726.webp



With the frictionless wall method.
Taking moments about the pivot point for a single leaf:
mg /2( L1 cos ∝ ) + T( L1 sin∝) = mg (L1 cos∝ )
T = mg/( 2 tan ∝ ) = 80 / (2 tan 5° ) = 40 / .0875 = 457.1 kg tension @ 5°.

T = mg/( 2 tan ∝ )
T/g = m /( 2 tan ∝ ) = 80 / (2 tan 5° ) = 40 / .0875 = 457.1 kg tension @ 5°.
T = 457.1 kg * 9.81 m/s^2 = 4483.2 N
 
Last edited:
Baluncore said:
making 80 kg total at the top
Should be 2P/2=40 for one leaf at the top.
 
256bits said:
457 kg tension at 5°
kN?
 
  • #10
berkeman said:
kN?
Edited Post #7
thanks.
 
Last edited:
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