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#1
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Pedersen self energizing brakes.
Every day is an adventure for a new bike mechanic. There seems to be n end to the exotic componentry out there. I just had a unit come in with the Pedersen cantis. It was easy enoug to figure out how they work, the only real mystery is, well, why? I a certainly no engineer,so maybe someone who is can explain the advantag if there is one. How does moving the pads forward as the brake arm rotate toward rim contact energize the brake? Was this just another answer to a question no one asked -- Dan Burkhar |
#2
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Pedersen self energizing brakes.
On Mon, 6 Jun 2005 13:18:52 +1000, Dan Burkhart
wrote: Every day is an adventure for a new bike mechanic. There seems to be no end to the exotic componentry out there. I just had a unit come in with the Pedersen cantis. It was easy enough to figure out how they work, the only real mystery is, well, why? I am certainly no engineer,so maybe someone who is can explain the advantage if there is one. How does moving the pads forward as the brake arms rotate toward rim contact energize the brake? Was this just another answer to a question no one asked? You answered one of your own questions he "How does moving the pads forward as the brake arms rotate toward rim contact energize the brake?" Look at this statement backwards - the brake arms rotate towards the rim as they move forwards. When the rider squeezes the lever, the brake blocks make contact with the rim. Friction between the rim and the block means that the block and its attached arm are dragged forward. The forward motion causes the arms to move inwards somewhat, causing an increase in the force holding the block againast the rim. Other manufacturers produced similar designs - the only one I could remember off the top of my head being Scott. Interestingly, the first Google hit for "Scott self energizing brake" is a section on John Forester's site relating to a lawsuit: http://www.johnforester.com/Articles...ng/sebrake.htm Hit No. 2 is Sheldon's site: http://www.sheldonbrown.com/gloss_sa-o.html#self As to they're being an answer to an unasked question, probably so. So much "innovation" and "development" in bicycle tech seems to be a marketing (rather than market) led drive to obsolete current components in order to keep customers on the purchasing treadmill. |
#3
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Pedersen self energizing brakes.
Dan Burkhart wrote:
Every day is an adventure for a new bike mechanic. There seems to be no end to the exotic componentry out there. I just had a unit come in with the Pedersen cantis. It was easy enough to figure out how they work, the only real mystery is, well, why? I am certainly no engineer,so maybe someone who is can explain the advantage if there is one. How does moving the pads forward as the brake arms rotate toward rim contact energize the brake? Was this just another answer to a question no one asked? I have a pair sitting around in the spares box. I never thought they had any more power than regular brakes when I used them (they came with a bike). Anyway, there's a helix in there which applies the brake harder as the pads are dragged forward by the rim. |
#4
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Pedersen self energizing brakes.
Zog The Undeniable wrote:
I have a pair sitting around in the spares box. I never thought they had any more power than regular brakes when I used them (they came with a bike). Anyway, there's a helix in there which applies the brake harder as the pads are dragged forward by the rim. I have a pair made by Sun Tour - they were only for back brakes I think. I replaced with V brakes which work better, although my old U-Brake on my Muddy Fox is pretty good too. |
#5
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Pedersen self energizing brakes.
the answer is!!! http://www.vintagebike.co.uk/Bike%20...rel%201929.htm and the question is!!! why does it not work?? |
#6
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Pedersen self energizing brakes.
check the Velocette Venom 500!!!
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#7
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Pedersen self energizing brakes.
Zog The Undeniable wrote: Anyway, there's a helix in there which applies the brake harder as the pads are dragged forward by the rim. OK, I understand that is the theory. What I don't grasp is how the brake can be applied "harder" without a corresponding increase in the force at the brake lever (through the cable), where the riders grip is the only thing securing the brake lever. Is this perhaps just a matter of anatomy where it is easier for the hand to resist a force statically than it is to dynamically apply the same force? Am I missing something somewhere? DR |
#8
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Pedersen self energizing brakes.
Dirtroadie wrote: Zog The Undeniable wrote: Anyway, there's a helix in there which applies the brake harder as the pads are dragged forward by the rim. OK, I understand that is the theory. What I don't grasp is how the brake can be applied "harder" without a corresponding increase in the force at the brake lever (through the cable), where the riders grip is the only thing securing the brake lever. Is this perhaps just a matter of anatomy where it is easier for the hand to resist a force statically than it is to dynamically apply the same force? Am I missing something somewhere? DR The rotating force of the wheel pulls the pad forward.. the mechanism then forces the pads tighter into the rim.. they worked OK when installed correctly.. except on some bikes where most of the extra force went into forcing the canti pegs outward (the stays would twist) the GT triple triangle were the worst. Adding a brake booster would fix the stay flex and then they worked quite well (assuming they were installed correctly) |
#9
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Pedersen self energizing brakes.
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#10
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Pedersen self energizing brakes.
Dirtroadie wrote: wrote: The rotating force of the wheel pulls the pad forward.. the mechanism then forces the pads tighter into the rim.. You are missing my point. The leverage between the brake lever and the cantilever arm does not change in any meaningful fashion once the brake pad is in contact with the rim. If the brake shoe is pushed against the rim with more force by the wedging action which results from the helical movement, something must resist that force, i.e., the tension in the brake cable must increase. What is resisting the force is the spring mechanism in the canti itself.. to some extent all you are doing with the brake lever is positioning the pads in such a way as to allow the rotating force of the wheel to engage the brake.. (not actually true.. there is sort of a shared increase between the spring and the cable but after the mechanism is engages the cable doesn't need to change in length of pull). If the tension in the cable increases then the force required at the lever must also increase. The seemingly erroneous assumption is that the cantilever arms are somehow immovably anchored. Most comments about these brakes indicate that they seem to increase braking performance. However for the reasons noted above the explanation which is given does not entirely make sense in that it suggests that "free" extra force is generated. I agree nothing is free... the spring mechanism is using the force of the wheels rotation to help cancel it.. that is where the "free" energy comes from. I have a set stashed away somewhere that I acquired for use on a tandem but I have never used them (anybody want to make an offer?). |
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