[TowerTalk] Tram rope

[Jim Lux]

At 12:38 PM 12/19/2006, Eric Scace K3NA wrote:
>Hard to draw a diagram on a text-oriented reflector.  If you read 
>this message with a fixed width font it should work reasonably well.
>
>First, the tram line in this diagram is like the gondola lift you 
>sited, Jim.  Tram wire sits overhead, and the sheave of a pulley rides on it.
>The antenna dangles below, and attached to, the frame of the pulley.
>
>Sketch at the point where the pulley rests on the tram:
>
><-- tower is towards the left.
>
>\
>\
>  o._
>  |  '-._
>(ant)    '-._ tram line continues off to right toward ground anchor.
>
>There are three force vectors meeting at the pulley:
>   -- antenna weight, points straight down.  100 lb in this example.
>   -- up toward the tower to the left.  I used 45 degrees in my 
> quickie statics example.
>   -- to the right down to the ground.  I used 30 degrees below horizontal.
>If you resolve the last two vectors into vertical and horizontal 
>components, you can create two equations with two unknowns, and solve.
>
>Of course, I did the algebra without the benefit of a morning cup of 
>coffee... and got wrong answers.  The answers for a 100 lb antenna should be:
>   333 lb up toward the tower
>   273 lb down toward the ground anchor

That's more what I would think. 700 lbs just seemed a bit too high.

Got it...