capstan

9 Articles

Cable Mechanism Maths: Designing Against The Capstan Equation

January 26, 2021 by 20 Comments

I fell in love with cable driven mechanisms a few years ago and put together some of my first mechanical tentacles to celebrate. But only after playing with them did I start to understand the principles that made them work. Today I want to share one of the most important equations to keep in mind when designing any device that involves cables, the capstan equation. Let some caffeine kick in and stick with me over the next few minutes to get a sense of how it works, how it affects the overall friction in your system, and how you can put it to work for you in special cases.

A Quick Refresher: Push-Pull Cable Driven Mechanisms

But first: just what exactly are cable driven mechanisms? It turns out that this term refers to a huge class of mechanisms, so we’ll limit our scope just to push-pull cable actuation systems.

These are devices where cables are used as actuators. By sending these cables through a flexible conduit, they serve a similar function to the tendons in our body that actuate our fingers. When designing these, we generally assume that the cables are both flexible and do not stretch when put in tension. Continue reading “Cable Mechanism Maths: Designing Against The Capstan Equation” →

Beautiful Moving Origami Light Made From Scrap

November 22, 2018 by 3 Comments

Whenever [MakerMan] hits our tip line with one of his creations, we know it’s going to be something special. His projects are almost exclusively built using scrap and salvaged components, and really serve as a reminder of what’s possible if you’re willing to open your mind a bit. Whether done out of thrift or necessity, he proves the old adage that one man’s trash is often another’s treasure.

We’ve come to expect mainly practical builds from [MakerMan], so the beautiful ceiling light which he refers to as a “Kinetic Chandelier”, is something of a change of pace. The computer controlled light is able to fold itself up like an umbrella while delivering a pleasing diffuse LED glow. He tells us it’s a prototype he’s building on commission for a client, and we’re going to go out on a limb and say he’s going to have a very satisfied customer with this one.

Like all of his builds, the Kinetic Chandelier is almost entirely built out of repurposed components. The support rods are rusty and bent when he found them, but after cutting them down to size and hitting them with a coat of spray paint you’d never suspect they weren’t purpose-made. The light’s “hub” is cut out of a chunk of steel with an angle grinder, and uses bits of bike chain for a flexible linkage.

Perhaps most impressive is his DIY capstan which is used to raise and lower the center of the light. [MakerMan] turns down an aluminum pulley on a lathe to fit the beefy gear motor, and then pairs that with a few idler pulleys held in place with bits of rebar welded together. It looks like something out of Mad Max, but it gets the job done.

Finally, he salvages the LED panels out of a couple of cheap work lights and welds up some more rebar to mount them to the capstan at the appropriate angle. This gives the light an impressive internal glow without a clear source when viewed from below, and really gives it an otherworldly appearance.

This isn’t the first time we’ve seen a hacker put together their own chandelier, or even the first time we’ve seen it done with scrap parts. But what [MakerMan] has put together here may well be the most objectively attractive one we’ve seen so far.

Continue reading “Beautiful Moving Origami Light Made From Scrap” →