Crash Restraint News & Updates

Mechanical Advantage and Friction in Suspension Lifts

Topologist

Introduction

While there is a variety of common wisdom regarding the effects of mechanical advantage and friction on suspension lift lines, the only published charts I'd ever seen attempting to quantitatively illustrate the subject were speculative and presented conclusions seemingly defying the laws of physics.

I've finally had some time over the past few weeks to explore this issue in more depth, first developing a mathematical model of the system, and then performing some experimental measurements to test the predictions of the model and determine the relevant coefficients of frictions. What follows are my conclusions from that work.

For background on the type of lifting setup which is discussed herein, please see this illustrated article.

Lifting Force

Let us imagine you are lifting a 100 lb bottom in a single-point suspension -- or, alternately, that you are lifting 100 lb worth of the body weight of a heavier bottom (for example, lifting their hips while their chest is...

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Attaching Support Lines

Topologist

When attaching support lines to a harness for suspension, I use a novel method that people frequently ask me about, and I've been meaning to document for a long time. Serendipitously, I ran into Kali from Kink Academy a few months ago at Wicked Grounds, and she asked me to film some instructional videos for them on suspension -- so I managed to slip this in there, and they've graciously agreed to allow me to use screenshots from those videos to illustrate a blog post here.

This method was inspired by the Tatu hitch, during a Fetlife discussion whose details are now murky in my memory -- in any case credit is due both Tatu and Jack Elfrink for making me aware of that knot, upon which this is based. Things needing names, and this technique using the first half of a Tatu hitch, I suppose we could call it the half-Tatu hitch.

Thanks also to Mecha-Kate for modeling for these. The full video version, in two parts, is here and here on Kink Academy. It's not free, but...

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