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Engineers, I'm in need of some help. The chain motors and some of the rigging we use at the theatre are rated in kN(kilonewtons), which is a measurement of dynamic load capacity. The problem is that many of the speakers I fly or other things are rated in just their weight. What is the connection between the dynamic load rating in kN and how much static weight said system can safely lift?

not from a text book per se .. but wiki says its .112 tons per kilonewton - 224 lbs.

the actual definition of kilonewton is:

Kilonewton, Mass
The newton (symbol: N) is the SI unit of force. It is named after Sir Isaac Newton in recognition of his work on classical mechanics.A newton is the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second squared.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Thanks, Tony. I guess my question is whether there is a difference between the value as defined which is a dynamic measurement and a static load you want to lift.

Some of the stuff we lift is very heavy. For example, the 2002 production of Man of La Mancha, with Brian Stokes Mitchell and Mary Elizabeth Mastriantonio, had a semi-circular wall of sheet metal and tubular aluminum that was 40 feet wide, 30' deep, and over 50' tall and split on the bias and the top section flew out. That wall, with none of the other set gags, weighed in at 18,000lbs.

Go for static.

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Check my oil too, if you don`t mind,,,

Assuming a chain motor is something that pulls a chain I would guess the newton rating is the max tension rating in the chain that the motor acts on. If that's the case, then if the tension is exceeded ie. force due to gravity (weight), friction, acceleration, whatever, then you've exceeded its rating.

Hi David .. what kind of ratings are the motors - ie how much Kn ....

A friend worked for the company that designed the Toronto SkyDome (now rogers) roof trusses. They were designed to fly 45 tons ... the fist major test was a Stones tour, they flew 42 tons ..... everyone was there to check out if the thing would crash !!!!

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

From Memory, it's a while since I did engineering calcs,

The difference is not a matter of static or dynamic, but between weight and mass.

In the American system weight is a force in pounds created by mass being acted on by gravity
If you want to consider mass in isolation from gravity you use a unit called "slugs"

In the SI system mass is in Kg, force is in N .
To get the weight of a 1kg mass you multiply by 9.81m/s2 (gravity) gives you a force in N
So to go from Kn to pounds first divide multiply by 1000 to give N then by 9.81 to give KG
then multiply by 2.2 to give pounds

Which gives you the 224 ibs to the KN that Tony has quoted

The rating on the gear is a force independent of direction (which is why it is in KN rather than KG) and should have a suitable factor of safety built in.

I'm not ashamed to admit that I don't understand much of what you are talking about, but it must have to do with a Gosh-awful-big heavy guitar.

Ray

What Jeff (and Tony) said. I was hoping someone would put in the gravity calculation (the direction vector), as that's the only way Newtons really make sense from thinking about 'weight'.

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Thanks folks.

Marc, a chain motor is a motor with a hook on one side and a chain on the other. The motor pulls the chain into and out of the housing thereby changing its length. They can be hung in either configuration and for theatrical and rock and roll, usually come in capacities of 1/2, 1, and 2 ton sizes.

Tony, when McCartney played at the then MCI Center (now Verizon Center a/k/a the Phone Booth) a few years ago they were at the building's capacity, and similarly the building engineer came down to watch. It's interesting that such new buildings (Verzion Center was finished in 1997) are being confronted with higher and higher loads for concerts. If memory serves, McCartney was 23 53 foot semis worth of gear. The Stones, whey they played here were around 57 53' semis.

Yeah, and most of that was for Keef's bandana collection ....

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"