Torque calculations for logging winch

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Discussion Overview

The discussion revolves around the calculations of torque in a logging winch system, specifically focusing on the effects of gear and pulley sizes on torque and pulling force. Participants explore the relationships between torque, shaft diameter, and the mechanics of gear reductions in a hydraulic motor setup.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant proposes that a hydraulic motor generates 3000 ft-lbs of torque at 650 RPM, and discusses how this torque is affected by the sizes of pulleys and shafts in the system.
  • Another participant argues that changing the diameter of the shaft does not affect torque, emphasizing that torque is consistent at the shaft regardless of the diameter of the gear or pulley attached.
  • There is confusion about whether the pulling force at the end of a shaft or gear is the same regardless of size, with one participant questioning if a larger diameter shaft could pull the same weight as a smaller diameter shaft.
  • Some participants clarify that while torque remains constant, the force exerted changes with the radius of the gear or pulley, leading to different pulling capabilities.
  • One participant suggests that the total torque output after two gear reductions would be 25 times the input torque, assuming no frictional losses.
  • Another participant raises concerns about the practical implications of the calculated forces and whether the proposed sizes of components are appropriate for the torque and tension values discussed.
  • There is a discussion about the definition of torque and its measurement, with participants seeking to clarify the relationship between torque, force, and lever arm length.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between shaft diameter and torque, with no consensus reached. Some agree that torque is measured at the shaft, while others debate the implications of gear size on pulling force.

Contextual Notes

Participants note that assumptions about the sizes of components and their appropriateness for the calculated torque and tension values may not be valid. There are also unresolved questions about the practical application of the discussed calculations.

Who May Find This Useful

This discussion may be useful for individuals interested in mechanical engineering, physics, or anyone involved in designing or understanding winch systems and torque calculations.

  • #31
Yes. But put the crows foot at 90 degrees, and it stays the same. A U-joint will also seriously complicate the math.
 
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  • #32
Agreed :)
The U joint will change the torque sinusoidally from input to output as the joint rotates.
 
  • #33
Use 2 in line u-joints 90 degrees out of phase with each other. They will cancel each other out and give true torque. Lines of action must be parallel.
 
  • #34
Yes, just like the way they are designed in transport trucks.
The only reason why we are changing to CV joints for trucks (or trying to) is fatigue loads. Even though the input-output relation can be almost the same the intermediate shaft is subjected to repeated and reversed sinus inertial torque. This causes premature wear and eventual failure.
Anyways, this is way off topic LOL.

Cheers,
 
  • #35
I always wondered about drive shaft fatigue. I figured that they just threw enough material at it for infinite design life.
 
  • #36
Engineers try to design these components for infinite life, particularly when lives are involved. However, if we designed everything to last very long periods of time no one would need a new transportation vehicle in 50 years. This is bad for business. Moreover, the typical engineering approach to design such components is a nonlinear optimization problem. Optimizing performance, life, and cost all in one shot.
You could imagine over engineering a shaft so that it can handle 2000ft-lbs of torque for 20000 hours and use it on a device that only subjects it to 500 ft-lbs peak torque would affect the inertial performance of the device. All that extra mass can significantly affect the performance.

In short, we don't design things for infinite life most of the time. Just as long as possible given a certain cost and performance criterion.

Cheers,
 
  • #37
To add a bit to that. New engineering methods can reduce inertial affect and simultaneously increase its fatigue life. This however, is expensive to engineer and manufacture. Some of this involves composite materials and extensive finite element analysis and experimentation.
 

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