gross weight and a class 2 lever? 1

[weaselman]

I have a large piece of equipment that requires two over-head cranes to lift. The overall size not the weight requires a crane at each end. I want to know the gross weight for trucking. I have one digital crane scale. If one end is crane/scale lifted just off the floor while the other end is the fulcrum point and then repeated at the other end would not the combined scale weights equal the total weight? Is this a class two lever?

Wes

 

[MiketheEngineer]

IF and that is a BIG if the center of gravity (CG) is in the middle - then the loads on each end would be the same.

Go rent(buy) another scale to be sure

 

[Timelord]

weaselman,
Your method will work as long as the object remains level when you switch ends with the load cell.

Timelord

 

[drawoh]

MiketheEngineer,

If the weights at each end are different, you have the means to work out the centre of gravity. The total weight is still valid is it not?

This is all assuming the thing remains approximately level, of course.

JHG

 

[swearingen]

In addition to being level, you must lift at the points that are touching the ground.

Think of a simple beam with self weight supported at each end. If it is approximately level, the reaction at one end of the simple beam could be the floor, while the other would be your crane/scale. If you switch ends, clearly the total of the two loads you measured would equal the weight of the beam. However, if you switch ends, and some other part of the beam hits the floor other than the point you first lifted, you cannot add the loads together to get the total weight.



If you "heard" it on the internet, it's guilty until proven innocent. - DCS

 

[eromlignod]

You don't have to know the center of gravity. This is a very common method for weighing large objects. If you weigh it at its supports it is the same as the vertical reaction forces in a free-body diagram. The sum of the supporting forces is equal to the weight.

Don
Kansas City

 

[weaselman]

Thanks guys for your feedback. I think Swearingen has it right. Regardless of where the cog is, the equipment must be lifted at the point where it touches the ground at either end. You could find the cog on the equipment once you have the two weights. Ah! the simple beam finally sinks in.

Wes

 

[drawoh]

swearingen,

However, if you switch ends, and some other part of the beam hits the floor other than the point you first lifted, you cannot add the loads together to get the total weight.

An excellent point, although it depends on how you attach the crane. The worst case is that you will have to test three points. The weight and centre of gravity is still calculatable.

JHG

 

[eromlignod]

You're missing the point. The center of gravity is superfluous.

If you take a four-legged table and put the two legs at one end on a scale, then put the other two on a scale, the weight of the table is the sum of the two readings, regardless of the location of the c.g. This is freshman statics, guys.

Don
Kansas City

 

[MotorVib]

eromlignod is right

That is what I have done in the past. You can also come up with the CG. It wil be close as long as the angle is not no much.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[swearingen]

Of course eromlignod is right, but if you put the scale under two legs on one end and then put the scale under the table top 3/4 of the way to the other end, you CAN'T just add them up - this was my point.


If you "heard" it on the internet, it's guilty until proven innocent. - DCS

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