How do I calculate the required torque for a drum with a wire rope load?

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In summary, the conversation is discussing how to calculate the minimum torque necessary for a motor connected to a drum with a known weight acting on a wire rope. It is mentioned that the diameter of the rope and the number of wraps on the drum must be taken into account for an accurate calculation. A resource for winching is provided as an example. The conversation then focuses on the design of a motor and drum, with a question about the correct way to measure the drum radius.
  • #1
wzrdstrm
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I'm doing some work were its necessary to calculate the force acting on a drum via a wire rope. If I have a known weight acting on the rope already and I want to back calculate the minimum torque necessay for a motor connected to that drum to hold that load, do I add the diameter of the rope to the radius of the drum to do so?
 
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  • #2
It depends on how many wraps of cable you have on the drum. In general you will need to take into account the diameter of the wire for a couple of wraps on the drum.

Here's an example in off-road vehicle winching:

http://www.pangaea-expeditions.com/resources/winchworksheet/index.html
Winch capacity

One of the common misconceptions regarding winches is that the maximum rated winch capacity is available any time the winch is hooked up. Unfortunately, this is false. Maximum winch capacity is in fact determined by the number of layers of cable wrapped on the winch drum.
...
As you can see based upon this chart, the number of layers of cable or winch rope on the drum greatly affects the winch capacity. With the top layer losing almost half the pulling power.
 
  • #3
What sort of hoist system is this? If a crane or elevator, then all sorts of standards and requirements apply.
 
  • #4
Simple design only, not for commerical review/standards. We have a motor connected to a gear box (1:1) ratio, connected to a drum that has wire rope wrapped half way across the drum on the root layer (1st layer). What I am expecting is that that if the drum had a root diameter of 100 inches (including lebus grooving) and a roper diameter of 2 inches, for calculation purposes we would have an effective drum radius of 52 inches for the first layer. Is correct?
 
  • #5
Center of drum to center of rope. 51 inches. But if you measure carefully, the Lebus shell will probably make that number a little different. Just measure total diameter including the rope layer and divide by 2. Then subtract one inch.
 
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  • #6
Confused, why subract one inch? the total diameter would be

2 X Rope diameter + Root Drum Diameter
 
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What is force calculation on a drum?

Force calculation on a drum is the process of determining the amount of force or pressure being applied on a drum, which is a cylindrical container used to store or transport materials. This calculation is important for ensuring the safety and efficiency of drum handling and transportation.

What factors affect force calculations on a drum?

There are several factors that can affect force calculations on a drum, including the weight of the contents inside the drum, the size and shape of the drum, and the type of force being applied (e.g. compression, tension, etc.). Other factors such as temperature, humidity, and external forces should also be taken into consideration.

How is force calculated on a drum?

Force on a drum can be calculated using the formula F = P x A, where F is the force, P is the pressure being applied, and A is the area of the surface where the force is being applied. The units for force are typically in pounds (lb) or newtons (N) and the units for pressure are typically in pounds per square inch (psi) or pascals (Pa).

Why is it important to calculate force on a drum?

It is important to calculate force on a drum because it helps ensure the structural integrity of the drum and prevents overloading or damage. This calculation also helps determine the appropriate handling and transportation methods for the drum to ensure the safety of personnel and the contents inside the drum.

What are some common mistakes when calculating force on a drum?

Some common mistakes when calculating force on a drum include not taking into account all the factors that can affect force (as mentioned in the second question), using incorrect units or conversions, and not considering the potential for external forces such as wind or vibrations. It is important to carefully assess all factors and use accurate calculations to ensure the safety and efficiency of drum handling and transportation.

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