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October 23, 2015

Skylon Tower mk II- suspended tower by Bothasig Rover Crew

1st Bothasig Rover Crew previously built a suspended tower, which fell a little short of their own high expectations for it. Having conducted a thorough SWOT analysis of the construction, the crew headed out to Hawequas Scout Ranch to build an improved version.
After six hours' work for 16 Rovers and Senior Scouts, the new tower successfully stood suspended one meter off the ground. 

Here is an excerpt from the project report, discussing the overall objectives:
"Objectives  
In hindsight, our objectives could have been more precise in terms of how high we could raise the 
tower. Our objective was to simply outdo the Mk I tower in height raised and to do it without 
incident, which we did achieve with a raised height of 1m and no reported accidents. 
Considerations in achieving the objectives 
In the planning phase, it is possible to roughly predict the final height raised based on factors such 
as: 
• The height of the apex of the tripods in conjunction with the distance of the apex from the 
centre tower. These two factors have the greatest influence of the final height raised, and 
the remaining factors will merely maximise the geometric potential of the layout. 
o The higher the tripod apexes, the greater the potential is of the tower to be raised. 
Also, the greater portion of the pulling effort will be translated into a vertical 
component of force to pull the tower up (as opposed to the horizontal component, 
which is destructive in this case and should be kept to a minimal). 
o As with the previous explanation of the height of the apex, the same applies with 
the horizontal distance of the tripod apex to the centre tower. The closer the apex is 
to the centre tower, the greater the vertical component of the effort in the system. 
• The block and tackle ratios should be considered and based on the size of the structure, and 
the size/strength of your team.  
o We used a 3-2 pulley system, and had two people pulling on each of the 4 tackles. 
o This simply diagram should illustrate what kind of mechanical advantage (MA) you 
can obtain from each system. 
  
To work out the MA, you have to count the number of 
lines between the blocks and exclude the running end 
from the count. 
o The greater the MA, the better, but this will obviously 
be limited by the resources available to you. 
o We used a 3-2 pulley system which gave us a MA of 
5:1
• The man power is a consideration and should be maximised, especially if you are resources 
are limited with regards to the pulley system. With this construction, it is possible to have 
the team sub-divided to work on various components simultaneously.  
o If the size of the team is large enough, you can have people placing anchors, building 
the tripods, building the crow’s nest all at the same time. 
o When erecting the central pole, we had 40% of the team hauling on one guy line, 
50% lifting and supporting the centre tower, and 10% holding the opposing guy line 
to prevent any over shooting of the tower. 
o When raising the tower, we had two people per tackle and one person per guy line. 
Then we needed extra people to lock the block and tackles and to secure the guy 
lines. 
o We had between 9 and 10 people to build the structure, and 12 people to raise the 
structure. More would have been better because we had to let one person on one of 
the tackles to let go and run to lock the black and tackle, then tie off the line to the 
anchor, then those two from that anchor could assist everyone else, which is not 
ideal. "


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