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ABK vs inline eight

Tuomas Pöysti 2021 Edit March 2nd 2021: It seems I messed up my notes when conducting the experiments. The alpine butterfly loop to end load cases 1 and 2 were in the wrong order when I first published this article. This mistake has now been corrected in the text. It is, though, a prime example […]

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Anchor extension tests

Tuomas Pöysti 2021 The traditional wisdom warns against anchors that extend in case of one of the points failing. Of course every single real life anchor will change it’s shape when the load transfers from the original set of points to the new, reduced set, and this will inevitably result in some kind of extension […]

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Cowstail as a fall arrester

Tuomas Pöysti 2021 Let’s make one thing clear right away: Cowstail is not a fall arrest device. It must be used for suspension or positioning only, never as a belay system. Simply put, any slack in a connected cowstail should be carefully avoided. This article is purely ‘academic’. It should not be used as a […]

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Drop test physics IV

Tuomas Pöysti 2021 In the previous part, I managed to extract displacement data from a load cell dataset sampled from a small drop test. The original data was something like this: And the displacement data looks as follows (both have time in seconds as the horizontal axis): The lowest point What have we learned this […]

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Drop test physics III

Tuomas Pöysti 2021 In the previous part, I played with the data (force vs time) from a single drop test and saw what I could do using the concept of impulse. It did not much to help understanding how energy is dissipated during a small fall on a static lanyard, but was fun, though. Now […]

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Drop test physics II

Tuomas Pöysti 2021 This part is a bit of a warmup. If you need a refresh on physics for this, see the first part. I am one of the “never fall onto your cowstail” type of instructors. Of course we all know you should not do that, but some of us tend to put more […]

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Drop test physics I

Tuomas Pöysti 2021 I don’t have a drop test tower. I don’t even have a proper lab with solid anchors. That’s ok, because I don’t have a real need for professional test setups, either. I play with my load cells to learn. Sometimes the sweetest bits of learning take place when figuring out how to […]

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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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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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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 […]