Pulley system composition – a systematic approach (2020)
Comments
araes
aidenn0
The 4th item in the top row of the first image is the Luff Tackle, using the authors rule that you can invert any combination and subtract one from the advantage; the non-inverted shown in TFA is 1:4 and the luff tackle is inverted and 3:1.
araes
Cool, thanks. Why I said "appears". Figured I was probably missing something. Author has spent way more time on pulleys.
jzwinck
1/2:1 is not useless. Sometimes you want to pull a rope quickly and power is not a problem. One real world use of a 1/2:1 pulley system is in high performance sailing dinghies on the spinnaker halyard. You want to be able to hoist it as quickly as possible, before the wind puts pressure on the spinnaker.
raelming
Just about every forklift uses a 1/2:1 pulley system in the the chains that lift the fork carriage up the mast. The main lifting pistons push a pulley upwards with chains tied to the fork carriage and mast base routed through the pulley.
araes
Maybe I don't understand what you're describing. That sounds like a system where you'd prefer slow, and really heavy lift capacity?
araes
Thanks. Figured there might be something, why the "might" have a use.
Maybe it's implied, yet the author didn't seem to care about fast, and mostly appeared to be counting whole numbers for greater lift. Guess most of the furthers probably also have uses if force is not an issue 1/3:1, 1/4:1, ect...
Sailing's not one I'd thought of much. Guess if large scale sailboats ever make it around again, hauling large scale ripstop nylon clipper sails might use a really fast spinnaker halyard.
poszlem
Pulleys are one of those things you never realize you need until you learn about them. Then, you suddenly understand just how useful they can be. Understanding the basics of rope rigging, pulleys, and mechanical advantage has made my life so much easier. Whether it's camping, hanging hammocks and tarps, using a pulley system to pull out tree stumps, securing things to my bike or pickup truck, or carrying a lot of gear at once, all of this becomes much simpler once you grasp the fundamentals of pulleys.
I honeslty think this should be taught in school, not just in physics classes, but as part of some kind of a "Life 101" course.
esaym
Kind of like knots...
tempnow987
Pulleys and knots can go hand in hand.
With ropes you can start with a basic loop that acts as a pulley. Butterfly, wireman's loop, farmers something - I forget the names.
But you basically create a loop that let's you double back your rope. With a lot of modern rope they are slippery enough you get pretty good mechanical advantage. Some folks then go to a taught line hitch or something to even keep things adjustable basically. Key is usually to give yourself enough space to tighten, and I skip the taughtline hitch in most cases.
Geee
A differential hoist [0], while not really a pulley system, is a quite interesting simple machine, which can generate infinite mechanical advantage. It has two sprockets which are connected on the same shaft. A chain loops through both of them in opposite directions so that the other wheel is feeding and other is pulling, and the load moves only by the difference of the wheel diameters.
quickthrowman
The common/trade name for this is chain fall or chain hoist, and widely used by tradesmen to lift heavy objects when a Lull (material handling forklift) isn’t an option.
raelming
Modern chainfalls use one loop of chain to drive a gear reduction which drives a separate load chain. Differential chain hoists with an upper and lower pulley and no gear reduction are found in museums.
istjohn
They are forgetting that pulleys can be coaxial.
esafak
I was waiting for the mathematical abstraction or software analogy; obviously, there's some composition going on.
Syzygies
Yes! Which entry in https://oeis.org (The On-Line Encyclopedia of Integer Sequences) is this?
If the author reads this, since it's from 2020. The author appears to be currently investigating knot physics and drop tests.
However, the author does not "appear" to have the Luff Tackle variation. [1] I think it's close to the 6:1 variation on row two, except with the pulley directly attached to the ceiling.
The systematic approach seems to work, just appears to be missing a few combinations, or it was not really systematic. Such as, their should probably be a lot of pulley combinations that are basically "nothing", or "not helpful" combinations. 1:1, or 1/2:1, ect... combinations that just noted as discarded (or maybe curiosities that "might" have a use)
A 1:1 pulley is not "technically" significant from this perspective, yet it does change the force direction.
[1] https://en.wikipedia.org/wiki/Pulley#Method_of_operation