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mechanical details on the movement of the Campagnolo 8sp rear derailleur

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mechanical details on the movement of the Campagnolo 8sp rear derailleur

Old 09-20-23, 08:23 AM
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mechanical details on the movement of the Campagnolo 8sp rear derailleur

hi
suppose you have
  • a Campagnolo 8 speed rear derailleur, say a Mirage short cage
  • a Campagnolo 8 speed dx ErgoPower, say a Mirage one
  • a Camapgnolo 8 speed sprockets cassette, 8 cogs of 1.9mm and 7 spacers of 3.1mm
I have the following doubts:
  • How many mm does the rear derailleur cable move each time you change gear with Ergopower?
  • How much force (in Netwon unit) is needed to move the rear derailleur one click?
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Old 09-20-23, 02:51 PM
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first things first... those are questions, not "doubts".

second thing.. WHY are you asking those two Questions?
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Old 09-20-23, 04:07 PM
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Fig Newton units...
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Old 09-20-23, 04:17 PM
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Originally Posted by maddog34
WHY are you asking those two Questions?
I'm designing a gear shift control, in addition to that I have the following doubt:

from what I understand, what really matters for changing gear on the rear derailleur should only be the cog-to-cog distance (center to center), which in the 8speed case must be 5mm with tolerance +/- 0.1mm, but I am not sure if for an indexed level shifter or for an Ergopower what matters is the thickness of the spacer (between two cogs), which in the case of 8 speeds should be 3.1mm? with a tollerance of what?

From the measurements I made on my bicycle it seems that only the thickness of the spacers matters, because the cable moves exactly 3.1mm, but I doubt that this is correct, because something doesn't add up to me.

I need to find a way to make measurements on the force needed to move the derailleur from one sprocket to another in flat conditions.

I need both these two points to size the components well.
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Old 09-20-23, 04:21 PM
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Pst, there is some designed play in most rear dlr pulleys...
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Old 09-20-23, 04:35 PM
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Originally Posted by wheelreason
Fig Newton units...
Yup, I can dimension things in terms of
  • static force: 5N, 10N, 20N, 30N, ... 50N, ... (maintain position)
  • dynamic force: 10N, 20N, 30N, 40N, ... 80N, ... (change position)
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Old 09-20-23, 04:36 PM
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Originally Posted by wheelreason
Pst, there is some designed play in most rear dlr pulleys...
good point, I have to investigate about this.
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Old 09-20-23, 05:10 PM
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Originally Posted by DiTBho
I have the following doubts:
  • How many mm does the rear derailleur cable move each time you change gear with Ergopower?
  • How much force (in Netwon unit) is needed to move the rear derailleur one click?
It's easy to measure cable movement, because it's a cable that moves, so get your ruler and measure a click. Now figure out how to get a more accurate result. The force is a bit trickier, you'll need to split the cable in the middle and attach a digital scale.
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Old 09-20-23, 05:47 PM
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Originally Posted by DiTBho
I'm designing a gear shift control, in addition to that I have the following doubt:

from what I understand, what really matters for changing gear on the rear derailleur should only be the cog-to-cog distance (center to center), which in the 8speed case must be 5mm with tolerance +/- 0.1mm, but I am not sure if for an indexed level shifter or for an Ergopower what matters is the thickness of the spacer (between two cogs), which in the case of 8 speeds should be 3.1mm? with a tollerance of what?

From the measurements I made on my bicycle it seems that only the thickness of the spacers matters, because the cable moves exactly 3.1mm, but I doubt that this is correct, because something doesn't add up to me.

I need to find a way to make measurements on the force needed to move the derailleur from one sprocket to another in flat conditions.

I need both these two points to size the components well.
umm... ok...
here's some basic info you NEED to consider before you waste another minute on your "project"...

https://bike.bikegremlin.com/1278/bi...20each%20click.
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Old 09-20-23, 05:52 PM
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you'll also be needing this...

https://www.omnicalculator.com/math/trigonometry
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Old 09-20-23, 05:53 PM
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CampagnoloCampagnolo has two standards of rear shift ratio. Old 1.4 and new 1.5. Also, not every shifter pulls the same amount of cable with each click. With 10 speed for example, there is more cable pull for “slower” speeds, than there is for the others. 2.5 mm pull five times (from smallest 1st to the 6th sprocket), 3 mm for 7th and 8th, then 3.5 mm for 9th and 10th. 2.83 mm average cable pull per click. 🙂

Apart from that, as of 2014 (don’t take my word for the exact year), campagnolo introduces another 11 speed standard. Previous Revolution 11 and the newest Revolution 11+. They are not compatible.

Since Campagnolo cassettes sprocket spacing differs from other manufacturers’, it is hard to combine Campagnolo RDs with anything but the appropriate Campagnolo shifters and in most cases cassettes too.
this confirms what I measured.
Thanks!
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Old 09-20-23, 05:57 PM
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Originally Posted by maddog34
trigonometry
specifically, for what?
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Old 09-20-23, 06:09 PM
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The derailleur moves to put the pulley beneath the cog - 5mm. That 5mm is the sum of spacer and cog thickness.

That said, the derailleur is not moving the same amount per shift, because it is moving in an arc. So the shifts between the high gears (small cogs) take more cable to produce a 5mm lateral move than what is needed for the lower cogs on a different part of that arc.

And then you have the fact that the derailleur spring increases tension as you shift lower.
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Old 09-20-23, 06:47 PM
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Originally Posted by DiTBho
specifically, for what?
if you don't know, you should quit wasting your time.
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Old 09-20-23, 06:55 PM
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Originally Posted by DiTBho
this confirms what I measured.
Thanks!
actually,,, No, it does not.
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Old 09-20-23, 07:02 PM
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Originally Posted by maddog34
if you don't know, you should quit wasting your time.
you mentioned trigonometry: I asked you what it applies to in this specific case? do you have a formula?
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Old 09-20-23, 07:10 PM
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Originally Posted by maddog34
if you don't know, you should quit wasting your time.
BS. Early index systems were designed without any math at all, so your "I have a secret" nonsense is just insulting. You don't know what the OP is doing and you aren't qualified to be making any judgements.
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Old 09-20-23, 07:12 PM
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Originally Posted by DiTBho
you mentioned trigonometry: I asked you what it applies to in this specific case? do you have a formula?
I would ignore him. He's hardly an expert on anything.
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Old 09-20-23, 07:13 PM
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have fun + good luck = i'm out

check my math if you wish.

here's a clue.. a TEN speed cassette is Not the Same as your 8 speed cassette.

here's another clue... a 3.1mm spacer is not all you need to "consider".

and finally... Study a modern Rear derailleur, then look up parallelograms... you just MIGHT discover a use for that trig. calculator.

you know.. i learned something in this thread... Campy cuts corners when designing their shifters.. hmmm... i think i'll continue avoiding Campy drivetrains.
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Old 09-20-23, 07:18 PM
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Originally Posted by maddog34
actually,,, No, it does not.
Actually it seems so, as I have 8 measures for 8 clicks, all between 3.0 and 3.1 mm, so from what I measure, the cable seems to always move the same amount for each click. From cog 1 to cog8.

Perhaps the deviation you speak of is there, but it is on the order of half a millimeter or less.

These are measurements made on the frame by placing an index on the cable and a reference on the frame, and measuring with a ruler with notches of one mm or half a mm, so the measurements have an uncertainty of +/-0.5mm, and must be redone on the ground with a twentieth caliper.

I have to buy/get an ErgoPower dx, a weight to keep the cable tensioned, and then repeat all the measurements on the test bench, this time with the caliper; the max travel for all 8 clicks is less than 30mm, and I have a caliber long enough

You mentioned an arc for the rear derailleur, but you didn't mention any formula, and that's the doubt I had too, but what you say could be wrong. I don't know.

Is there any tecnical document about this?
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Old 09-20-23, 07:21 PM
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Originally Posted by maddog34
have fun + good luck = i'm out

check my math if you wish.

here's a clue.. a TEN speed cassette is Not the Same as your 8 speed cassette.

here's another clue... a 3.1mm spacer is not all you need to "consider".

and finally... Study a modern Rear derailleur, then look up parallelograms... you just MIGHT discover a use for that trig. calculator.

you know.. i learned something in this thread... Campy cuts corners when designing their shifters.. hmmm... i think i'll continue avoiding Campy drivetrains.
Campy 8 speed derailleurs were essentially copies of the Shimano index derailleurs.

You're a troll.
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Old 09-20-23, 07:28 PM
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Originally Posted by Kontact
I would ignore him. He's hardly an expert on anything
I'm an electronic engineer, I have no experience with bicycle mechanics, if not the practical mechanical skills that have allowed me to carry out routine maintenance on my road bike (Litespeed Classic, 1997, Campagnolo Mirage 8sp) for the last ~30 years.

so what?
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Old 09-20-23, 07:31 PM
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Originally Posted by DiTBho
Actually it seems so, as I have 8 measures for 8 clicks, all between 3.0 and 3.1 mm, so from what I measure, the cable seems to always move the same amount for each click. From cog 1 to cog8.

Perhaps the deviation you speak of is there, but it is on the order of half a millimeter or less.

These are measurements made on the frame by placing an index on the cable and a reference on the frame, and measuring with a ruler with notches of one mm or half a mm, so the measurements have an uncertainty of +/-0.5mm, and must be redone on the ground with a twentieth caliper.

I have to buy/get an ErgoPower dx, a weight to keep the cable tensioned, and then repeat all the measurements on the test bench, this time with the caliper; the max travel for all 8 clicks is less than 30mm, and I have a caliber long enough

You mentioned an arc for the rear derailleur, but you didn't mention any formula, and that's the doubt I had too, but what you say could be wrong. I don't know.

Is there any tecnical document about this?
"half a millimeter" is 15 or more percent of the travel you doubt measuring correctly.

etc.

i am now leaving my shop and getting some dinner. Thai food, fresh rolls with peanut sauce and special curry with chicken or prawns, haven't decided yet,.to be specific. Bye.
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Old 09-20-23, 07:39 PM
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Originally Posted by DiTBho
I'm an electronic engineer, I have no experience with bicycle mechanics, if not the practical mechanical skills that have allowed me to carry out routine maintenance on my road bike (Litespeed Classic, 1997, Campagnolo Mirage 8sp) for the last ~30 years.

so what?
If I am talking to you by quoting you, I would not call you "him".

I was telling you to ignore Maddog34 because he doesn't know what he's arguing about. You don't need trig to approximate the basic operation of a derailleur. You can even analyze it closely with a ruler and a compass on paper, if you account for all the angles.

But you don't even need to do that - all index derailleurs are friction derailleurs with a shifter that mimics a precise friction shift. Shimano waited until they could use Suntour's friction derailleur patent to launch modern index derailleurs - they didn't invent anything, just got the details right. Suntour and Campy followed by doing even less engineering, but getting their existing derailleurs to shift primarily by designing a shift lever. Suntour and first gen Campy index systems all work really well with later ramped cogs, because indexing is not that hard.

I don't know what you are up to, but the fact that mechanical index systems are still based on friction derailleurs is the primary problem with them. If you are doing something to address that - great. I have my own design, but the bike industry has moved on.
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Old 09-20-23, 07:43 PM
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Originally Posted by Kontact
Campy 8 speed derailleurs were essentially copies of the Shimano index derailleurs.
Nice to know =)
I could also buy/get Shimano parts.

I don't have anything made by Shimano.
I have a medium cage Sash/8sp rear derailleur, brand new, never used, which I was given as a gift. But I don't know how compatible it is with Campagnolo or Shimano, and I don't have any Sash shift stick.
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