Mechanical advantage is doing my head in!

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nirakaro
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Mechanical advantage is doing my head in!

Postby nirakaro » 6 Jan 2019, 6:25pm

I'm reading Sheldon Brown on the geometry of cantilever brakes, and can't make sense of it.
Specifically, he says that the shorter the yoke cable, the greater the MA. And conversely, the least MA will, in theory, come from an infinitely long yoke cable. But as I visualize it, pulling up on a very short yoke cable will move the brake pad a lot for a small pull, which, unless I'm misunderstanding the terminology, is a smaller MA. And as you lengthen the yoke cable, you need a longer pull to get the same movement of the brake pad. And with an infinitely long yoke cable, it would take an infinite pull on the brake lever to move the brake block at all. Which is an infinite MA, no?
What am I misunderstanding here?

landsurfer
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Re: Mechanical advantage is doing my head in!

Postby landsurfer » 6 Jan 2019, 6:31pm

Had really nasty squealing with the original cable set up on my Jamis Canti brakes .... i read Sheldon's article, bought some bits from SJS ... Shorter Cable = No Squealing !
It's just like that, it's just the way it is.
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rjb
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Re: Mechanical advantage is doing my head in!

Postby rjb » 6 Jan 2019, 6:46pm

Plough through this discussion viewtopic.php?f=5&t=57410
At the last count:- Focus Variado, Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin, Raleigh 20, Falcon K2 MTB dropped bar tourer, Longstaff trike conversion on a Falcon corsa. :D

jb
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Re: Mechanical advantage is doing my head in!

Postby jb » 6 Jan 2019, 7:01pm

The nearer the straddle wire is to a straight line the more force is transmitted to the cantilevers, you will find if you look carefully that the movement of the block is actually a lot less than the vertical movement of the wire.

An infinitely long wire on the other hand, will pull the cantilever straight up whilst transmitting virtually nothing to the movement of the block
Cheers
J Bro

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cycleruk
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Re: Mechanical advantage is doing my head in!

Postby cycleruk » 6 Jan 2019, 8:16pm

nirakaro wrote:I'm reading Sheldon Brown on the geometry of cantilever brakes, and can't make sense of it.
Specifically, he says that the shorter the yoke cable, the greater the MA. And conversely, the least MA will, in theory, come from an infinitely long yoke cable. But as I visualize it, pulling up on a very short yoke cable will move the brake pad a lot for a small pull, which, unless I'm misunderstanding the terminology, is a smaller MA. And as you lengthen the yoke cable, you need a longer pull to get the same movement of the brake pad. And with an infinitely long yoke cable, it would take an infinite pull on the brake lever to move the brake block at all. Which is an infinite MA, no?
What am I misunderstanding here?

In my mind a short yoke cable will give a greater force on the pads than a longer one for any given force on the brake lever.
So therefore has more of a mechanical advantage. :roll:

My set-up to give best braking =

In theory the angle between the red and blue lines should be about 90 degrees when the pad hits the rim.
Oryx copy.jpg

In practice.
Image Attachments
Straddle cable (Large).JPG
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531colin
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Re: Mechanical advantage is doing my head in!

Postby 531colin » 6 Jan 2019, 9:37pm

rjb wrote:Plough through this discussion viewtopic.php?f=5&t=57410

^^^^^^^ Wot E said!!

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NATURAL ANKLING
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Re: Mechanical advantage is doing my head in!

Postby NATURAL ANKLING » 6 Jan 2019, 10:37pm

If You Don't Try You Don't Do.....Don't Do You Don't Get...I'm Still Trying....Well Very..
You'll Find Me At The Top Of A Hill...............Somewhere...After Dark..

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Chris Jeggo
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Re: Mechanical advantage is doing my head in!

Postby Chris Jeggo » 7 Jan 2019, 8:54am

531colin wrote:
rjb wrote:Plough through this discussion viewtopic.php?f=5&t=57410

^^^^^^^ Wot E said!!

^^ Wot they said!