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Articles in English

Pulley system composition – a systematic approach

Tuomas Pöysti 2020 This article builds on the basic theory of pulley systems and partly on my method of analyzing pulley systems. The English texts are quite recent as I’m writing this, but they are based on older texts and ideas. I’m constantly (or at least in recurring bursts) learning more about pulley systems, and […]

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Articles in English

Line deviation and pulley efficiency, part II

Tuomas Pöysti 2020 Earlier I did a little empirical study to compare one 180º deviation with two 90º deviations using a similar pulley. I thought it would be nice to have some data points on other angles than those two. To be exact, I never even measured a single 90° deviation, but calculated a hypothetical […]

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Articles in English

Line deviation and pulley efficiency

Tuomas Pöysti 2020 As I mentioned in the end of this article, the capstan equation cannot generally describe a rope-carabiner or a rope-capstan combination as a pulley. The rope’s internal part of friction is hard to explain where the rope does not undergo any deformation. Some notes on deformation If a rope is wrapped three […]

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Articles in English

Pulleys and different line materials

Tuomas Pöysti 2020 We already know that pulley efficiency strongly and undoubtedly depends on sheave diameter. It is easy to guess that it is not only sheave diameter, tough, but relation between sheave diameter and line thickness. This is something I have done some empirical studies with. The “pulleys” where: Pulley Camp Tethys Pro (28 mm sheave) […]

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Articles in English

Pulley efficiency: comparison with Petzl

Tuomas Pöysti 2020 I’m not fortunate enough to own a Petzl Maestro, or know anyone who would lend me one for efficiency testing. When I got the opportunity to test MPD and Clutch, I was fully aware that Clutch and Maestro would have been way more interesting pair. About the same time Petzl published an […]

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Articles in English

Clutch and MPD as pulleys

CMC/Harken Clutch and CMC MPD are very different devices. MPD weighs and costs about 40% more and clearly has different markets and usage. But there are similarities, as well. And I’m able to study both. My method of measuring pulley efficiency has no problems with PCD devices like these, since it does not require the […]

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Articles in English

Some pulley efficiency measurements

Tuomas Pöysti 2020 This is how I measure pulley efficiency. The method has evolved over time, but all values given here are from the latest iteration. I have carried out several different sessions, typically going through all of the pulleys I currently owned, and depending on interest of that time, different kinds of line materials, […]

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Articles in English

Pulley efficiency and sheave diameter

Tuomas Pöysti 2020 As we know, pulley efficiency has more to do with sheave/rope diameter ratio than bearings, bushings or other technical nuances of pulley design. To get rid of any doubts considering potentially different bearings on commercial pulleys of various sizes, I built a pulley with interchangeable sheaves. The sheaves range from 20mm to […]

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Articles in English

Low-efficiency PCD’s

Tuomas Pöysti 2020 In this article I studied how different pulley systems react to varying pulley efficiency, especially at low efficiency levels of carabiners. Mostly, all pulleys were considered equally inefficient. PCD (progress capturing device) is a special pulley in this sense. There are popular PCD’s that make even worse pulleys than carabiners. These include […]

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Articles in English

The ” best pulley closest to hand” rule

Tuomas Pöysti 2020 If you find my pulley system articles even a bit interesting, you probably are familiar with a basic rule of thumb regarding pulley systems (or “rule of fist”, as we appropriately say in Finnish): the most efficient pulley should be placed closest to the pulling hand. This has been proven many times […]