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Derailleur Pull Force

Old 12-15-18, 06:10 PM
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Derailleur Pull Force

How much force does it take to actually move a derailleur?
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Old 12-15-18, 06:22 PM
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Depends on the parallelogram return spring, whether there's any corrosion or grit in the pivots. If you are asking about the lever force add to the list any cable friction (quite variable), the shifter cable spool's diameter, the shifter's own pivot friction. If you're including engaging an adjacent cog (and not just moving the der a tiny bit) then the cogs' size difference, if there're any shifting aids in play (like a shift gate, twist teeth or chain side plate shaping) and how close to the cogs' undersides is the guide pulley. Add to that is that different models/brands of ders have different spring tensions and that the return spring can change over the years.

Why do you ask? And what do you really mean by "move"? Andy
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Old 12-15-18, 06:27 PM
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I guess you're not asking because it's too easy. I've seen the front derailleur start locking up because it had dried sport drink on it.
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Old 12-15-18, 06:31 PM
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Hi Andrew,

Move = Index a shift. I'm interested in experimenting with linear servo's for executing shifts; need to spec the right device. I have a SRAM X7 group set, just curious if it was something that was common...like 'it takes between 10-14lbs of pull to hold/move'. If it's one of those...it depends, then I'll have to get off the couch and measure it with a pull scale...just curious.

ron
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Old 12-15-18, 06:52 PM
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Great project. I honestly though you were trolling. If you're running a cable between the servo and the der it should be easy to measure shifting forces. I would suggest measuring other brands then just Shimano. The big S tends to have fairly soft return springs compared to other brands. Andy
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Old 12-15-18, 07:03 PM
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Yeah, something to pass the winter time.
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Old 12-15-18, 07:48 PM
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Originally Posted by rmueller View Post
Yeah, something to pass the winter time.
You do know it's been done, right? Shimano DI2, Campy ESP and SRAM eTap, all do exactly what you are proposing.
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Old 12-15-18, 08:23 PM
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Also take into account any clutch mechanism if mtn style as that adds some resistance when shifting to bigger dia cog.
Archer and Xshifter already use motors to "pull" the cable for wireless shifting.
No need to reinvent that.
Google them.
Good luck.
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Old 12-15-18, 10:41 PM
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Originally Posted by HillRider View Post
You do know it's been done, right? Shimano DI2, Campy ESP and SRAM eTap, all do exactly what you are proposing.
Yep, add Archer and XShifter to the list, all good solutions for some people.

Other than Shimano, none of them have a dedicated solution for trikes. Then there is the cost. The Archer seems to specialize on the rear der only. I don't think the XShifter is ready for production just yet. They do have a pretty cool approach.

Cold winter, not much to do when it gets really crummy outside, got bored and dreamt up a project to putz around with.

I knew I wasn't crazy when I couldn't find any documentation on how many lbs' it takes to pull a der spring back...no one has that answer yet. I'll measure it tomorrow.
@steveoo - actually, Archer seems to use an Acutonix linear servo. I'll bet XShifter uses something similar or the same thing. These things are ideal for the application. I won't necessarily re-invent it, but I will build a dual shift system for less than $250 in parts and have some fun doing it.

ron

Last edited by rmueller; 12-15-18 at 10:45 PM.
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Old 12-16-18, 11:19 AM
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Prepare your test, to get yout anawer

Originally Posted by rmueller View Post
How much force does it take to actually move a derailleur?
its SCIENCE !

Make a place to mount a derailleur and a cable you can keep adding wight onto.. and note how much weight you have added
to reach equilibrium with the force of the return spring..

you need to buy or borrow a gram scale to note the weight of each thing you are adding, pulling down on that cable...
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Old 12-16-18, 02:57 PM
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Originally Posted by fietsbob View Post
its SCIENCE !

Make a place to mount a derailleur and a cable you can keep adding wight onto.. and note how much weight you have added
to reach equilibrium with the force of the return spring..

you need to buy or borrow a gram scale to note the weight of each thing you are adding, pulling down on that cable...
So, you are just confirming...nobody knows how much force it takes. Sorry, thought it was a simple question. Went to the tackle box, thought I had an old scale...nope, Amazon will deliver one on Tuesday. I'll know how much it takes on Tuesday.

Thought it would be a relatively straight forward question/answer, fascinating that its just not commonly know or at least a range/guess.

Ron.
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Old 12-16-18, 05:55 PM
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I'm interested in experimenting with linear servo's for executing shifts; need to spec the right device..
so you are capable of solving this too, rather than outsourcing it...
Now, you have an opportunity to do the work. since it's quantity in numbers is valued ..



FWIW, I have a Shimano bar end with a spring in it,(in a parts bin)
last time I installed it, it was close to the return spring force of the FD,
so moving the lever was fairly effortless... As a mechanic that was close enough for me..




...

Last edited by fietsbob; 12-16-18 at 06:32 PM.
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Old 12-16-18, 05:55 PM
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It's a topic that does come up periodically here, but as a reference to "why is it so hard to..." I suspect if you do the testing on a wide range you'll find there's more difference with ft ders then rears. Specifically it seems to me that there's some front ders that have a high initial movement force that ramps down quickly. Andy
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Old 12-16-18, 11:11 PM
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Originally Posted by rmueller View Post
@steveoo - actually, Archer seems to use an Acutonix linear servo. I'll bet XShifter uses something similar or the same thing. These things are ideal for the application. I won't necessarily re-invent it, but I will build a dual shift system for less than $250 in parts and have some fun doing it.
ron
A friend has been running an Archer shifter on his recumbent trike. It looks pretty interesting and a way to eliminate the long cable runs on recumbents. So far it's worked OK.
https://www.archercomponents.com/
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Old 12-17-18, 10:56 AM
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Originally Posted by rmueller View Post

Thought it would be a relatively straight forward question/answer, fascinating that its just not commonly know or at least a range/guess.

Ron.
This couldn't be easier @rmueller, you need to set up an experiment, just as fietsbob said, but you're actually measuring lateral displacement as a function of force applied. Plot it and you'll be operating over the somewhat linear region. Cog spacing will be total displacement required, divided by the ((number of cogs - 1)+single cog thickness)), over some fraction of the total range of the derailleur you test. Set up several identical derailleurs to get a large enough sample, say 10 or so derailleurs.

Force will be equivalent to the weight, if you use a pulley system and neglect friction sources. You can add them in after the fact, but that will be another set of experiments, of course.

Easy. You could accomplish this in an afternoon...
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Old 12-17-18, 06:29 PM
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Originally Posted by Andrew R Stewart View Post
It's a topic that does come up periodically here, but as a reference to "why is it so hard to..." I suspect if you do the testing on a wide range you'll find there's more difference with ft ders then rears. Specifically it seems to me that there's some front ders that have a high initial movement force that ramps down quickly. Andy
I'm just as surprised the manufactures don't include a bit of that type of data in their specs. The only thing that they disclose is the torque needed for the screws.

ron
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Old 12-17-18, 06:34 PM
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Originally Posted by Jeff Wills View Post
A friend has been running an Archer shifter on his recumbent trike. It looks pretty interesting and a way to eliminate the long cable runs on recumbents. So far it's worked OK.
https://www.archercomponents.com/
The Archer looks like a really nice system. It's simple, their app looks pretty good and their shifter buttons look like you can actually work them with gloves on (even winter gloves). It's a sub $500 device, but you need two of them for front/rear setup. I'll probably use the same linear servo they use.

ron
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Old 12-17-18, 07:28 PM
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Originally Posted by rmueller View Post
I'm just as surprised the manufactures don't include a bit of that type of data in their specs. The only thing that they disclose is the torque needed for the screws.

ron
There's no need to list said cable pull tension. They all are within the range of human capability and that spec hasn't been marketed as important (unlike the brake lever pull force, as a comparative amount at least). Andy
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Old 12-17-18, 07:31 PM
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If there's an exposed portion of the shift cable, such as along the downtube, hang some weights and see how far it deflects. Then it's a bit of trigonometry.
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Old 12-17-18, 08:14 PM
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Originally Posted by Gresp15C View Post
If there's an exposed portion of the shift cable, such as along the downtube, hang some weights and see how far it deflects. Then it's a bit of trigonometry.
Actually Newtons 2nd law, pretty clever idea..."but I was told there would be no math"

While I was digging through the tackle box trying to find the fish scale (never did - ordered one comes tomorrow), I was also thinking about trying different fishing lines - tie it off and pull to see if it breaks; based on the line 'test' should be a simple experiment to get a range.

@andy - makes sense.
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Old 12-17-18, 08:40 PM
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That would be like doing a striper hit on a bluegill.
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Old 12-18-18, 06:41 PM
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FWIW...non-scientific measurement at the point the cable curves over the rear of the der 11-22lbs to move it (with the chain on the smallest gear, shifter set to put slack in cable). Starts at 11 then goes to 22, pretty sure the high measurement is because the chain isn't moving. I'll remove the shifter and pull on the actual cable while pedaling, I'm betting its going to be 11-15lbs. Its' probably close enough to be able to pick linear servo.
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Old 12-18-18, 07:28 PM
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I was on a group ride last week when a rider broke a RD cable. I thought no big deal, I'll just tie it off for him. But he had a Shimano 11-speed and I was shocked at the amount of tension compared to my Ultegra 9-speed RD. I understand that those brifters have smaller drums to reduce the lever force and increase cable sales. Plus he had internal routing, bummer. Silly IMO. At it turned out, we couldn't get the cable tension to hold and he had some big gears for the rest of the ride. Luckily the steep hills weren't long or very steep.
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Old 12-18-18, 08:42 PM
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Originally Posted by rmueller View Post
Yeah, something to pass the winter time.

Winter starts in 3 days, officially .. Solstice.. 21st..


I'm just as surprised the manufactures don't include a bit of that type of data in their specs
manufacturers sell truck loads full of of components to the bike factories individual sales is relatively a small sector...\




...

Last edited by fietsbob; 12-18-18 at 08:48 PM.
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