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 […]
Author: Tuomas
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) […]
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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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 […]
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, […]
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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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 […]
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 […]
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Using carabiners as pulleys
Tuomas Pöysti 2020 Once again, this is not a very practical article. Not a single photo. And I’m not going to give much direct answers or advice, but hopefully this will help someone coming into their own conclusions. Using pulley system analysis, we can systematically study some properties of different pulley systems. For example, we […]
We know that a good, relatively big pulley used with a 11mm nylon rope is actually only about 90% efficient. That is, 10% of energy is lost somewhere around the pulley. And a smaller pulley will lose even 20%. For example: if a 100kg weight is lowered 10m distance using a descender, the descender has […]