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# Rigging Weight Calculations

## Question

It would be great for Vectorworks to calculate point loads...

For example, I have a 40' truss on 2 points with say a 300 lb. point load 5' away from point 1. I would want it to do the math to say the point load on 1 is X and the point load on 2 is Y.

So with the new hoist to attach it to a truss... fixtures are already attached, put in a cable weight multiplier and safety margin and good to go.

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Hopefully one day, but it is not that easy.

First, currently VW does not understand weights. I know they are just numbers, but what happens when someone enters a weight in KG and the person using that data is expecting pounds. The load is 2.2 times higher. Who is responsible for the result?  So VW needs to understand weight units and automatically convert between them just as if currently does with linear and volumetric dimensions.

Second, there is no actual engineering formula for a system with more than 2 lifting points. If you put 3 chain hoists on a truss and lift it, it is "impossible" to calculate the load that will be carried by each of the hoists. As soon as you make a small adjustment to the length of one of the leads, the load carried by the other two changes. Often drastically. So even if you get the point load calcs, it is unlikely that VWI would ever take the risk of doing so for more than a 2 point lift.  It is easy for an individual to say "Oh, that is close enough." Much harder for a company with deep pockets to take that kind of a risk when they have no knowledge of how the resulting data will be used.

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Yes I agree. I would love for trusses to automatically calculate weight of cables and fixtures attached, and have chain motors pick up weights and other info through a connection to the truss.

I would be fine with only two point calcs at this point. Like Energos is only an estimating tool, I think a truss weight and chain motor capacity estimating tool would be very helpful, although it would need to be designated that it is not a substitute for proper mechanical engineering and rigging knowledge.

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