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 1926 Model TT Restoration: Rigging and Mechanical Advantage 
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Traut wrote:
Fascinating. I've used block and tackle arrangements all my life, logging, boating, material transfer, construction, etc, mainly getting my trucks unstuck. It's all PFM and a thing of beauty to me every time I see it in action. Being a lazy slob, I can't ever get enough of energy saving tech.

So Professor, for a given pulley arrangement, does "pulling" on the moving pulley always yield an increased advantage, as opposed to pulling on the fixed component? I'd be tempted to ask why, but the answer might make my head explode.

Yes. You get a +1 mechanical advantage when you haul on the moving pulley, vs the stationary pulley, no matter which type of tackle you use.

Image

And no way am I a professor. I knew next to nothing before I started to research all this stuff for the tow boom project. I think of it this way: the suspended load is being held up by a pulley threaded with a number of lines. Each line takes an equal portion of the load. If you are lifting 100 lbs with a luff tackle in rove disadvantage, that configuration has 3 lines reeved to the moving pulley, and each line is taking on 33.3 lbs. So the line you are hauling on takes 33.3 lbs to move the load (MA=3). If you thread the lines so you are luff tackle rove advantage, that configuration has 4 lines reeved to the moving pulley. Each line bears 25 lbs now, and you only have to haul 25 lbs to move the 100 lb load (MA=4). Of course you have to pull 4 feet of line to get one foot of lift with a MA=4, so increasing MA means you need to pull increasing amounts of line for the same amount of lift.

Now I have started collecting vintage pulleys, just because they are cool.


Last edited by Arisaka on Thu Feb 13, 2020 3:23 pm, edited 2 times in total.



Thu Feb 13, 2020 2:03 pm
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Once again you've demystified something I've suspected a long time. Makes perfect sense the way you explain it, Sensei. Wax on, whacks off. Simple! :bigsmile: thanks.

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Thu Feb 13, 2020 2:54 pm
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