Author Topic: Drop 'bars & Rohloff: A dozen differ'nt ways  (Read 54717 times)

Andre Jute

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #15 on: March 24, 2012, 10:23:37 PM »
Think of a purchase as an investment in scientific research Dan  ;)

For the Advancement of Physics!

Danneaux

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #16 on: March 24, 2012, 10:46:21 PM »
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For the Advancement of Physics!
Oh, now, Andre...that's just not fair!  How can I ever resist an argument like that?!?  ;D

Doomed Dan. (...who really would try a Rohloff Thorn if he had the ready cash for one. What's the Lotto totaling today?)

Danneaux

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #17 on: June 23, 2012, 06:44:49 PM »
Hi All!

Motivated by and exploring ways to fit the Rohloff shifter to drop 'bars has resulted in a couple of questions I am hoping might be answerable:

1) How much pressure is required to rotate the Rohloff shifter? Is it quite a lot (as in upshifting a trigger-shift), it is it more like a doorknob with little detents? Is there some means for comparison with an everyday or cycling task that could convey how much pressure is required for rotation? Can you give me some idea how freely turning the shifter is between detents and to move from a detent?

2) How many degrees of rotational movement is required for a shift the entire range, from "gear" 1-14.

Both these questions would be instantly answerable if I had one at hand to try, but I don't. Thanks very much; I have an idea in mind that is percolating away on the back burner.

Best,

Dan.

julk

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #18 on: June 23, 2012, 07:19:38 PM »
Dan,
1. More than using a rapidfire trigger shifter, less than using a gripshift, nearer to the gripshift effort but smoother - the gripshift goes to the next position with a sharp click.
I find it easier to keep rotating and get a multi gear shift with the Rohloff, limited only by my wrist rotation.

2. Going from gear 1 to gear 12 uses 240 of grip rotation precisely. So that would be (240 * 13 / 11) or 283.64
Julian.

rualexander

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #19 on: June 23, 2012, 07:27:08 PM »
Dan,

I would say the notchy door-knob analogy would be fairly close to the way the shifter feels, fairly light and easy to shift, and the rotational information is available on this page of the Rohloff website, 21 degrees per gear, or 273 degrees from top to bottom gear.

Danneaux

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #20 on: June 23, 2012, 08:17:56 PM »
Rual,

That's tremendously helpful; thanks! Just what I wanted.

Now I have the information, what I was pondering is the possibility of mounting the shifter inverted on a clamp-on post below the tops of a drop handlebar, then fitting the rubber grip with a clamp-on, winged or posted cylinder for thumb-finger push-pull operation. One of my drawings looks a bit like an old ship's wheel set horizontally. With "only" 230 of movement, perhaps only five posts would be needed, and all in a row rather than distributed 'round the grip.

I recently made a knob-assistive device for someone with hand movement and strength limited by a stroke. Got me to thinking about bicycle applications.

What I am pondering ss something that would allow alternate thumb-finger operation from the tops of drop 'bars, an effect somewhere between Shimano's RapidFire trigger shifters and the old SunTour Command shift ( http://thevintagefuji.blogspot.com/2011/07/suntour-command-shifters.html ) without adding complication or altering the Rohloff shifter internally. I envision a clamp-on adapter and post. Wouldn't take me long to machine a prototype, but I really can't go farther with the idea without an example at hand; I have nothing to model it on. Just thinking after spending some time with the machine tools this morning.

I think any successful drop-'bar solution will only really work if it is as simple and straighforward as the original Rohloff rotational shifter. If it could be adapted from same, so much the better.

Best,

Dan.

fleur

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #21 on: June 23, 2012, 08:20:23 PM »
For the effort, it actually changes depending on the load of the pedals.  The more load on the pedal, the more effort.  The door knob comparison is without load on the pedals.

For the grip rotation, this value is for the Rohloff grip.  But it depends of the diameter of the grip because what is needed is a given motion of the cable (the indexation is in the hub, the cable must move a given length to shift to the next gear, there are two cables, one to shift up from 1 to 14, the other to shift down from 14 to 1).  Some other grips for Rohloff have a different diameter and as consequence a different rotation (there is for instance a 360 degree grip).

Danneaux

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #22 on: June 23, 2012, 08:30:41 PM »
Thanks for that added observation, Fleur; very helpful as well!
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Some other grips for Rohloff have a different diameter and as consequence a different rotation
I see what you are saying, though the hub diameter (the part 'round which the cables are placed) must stay a constant size, even if the diameter of the grip changes.

A larger grip diameter would comprise a greater moment arm from the shifter's hub axle, effectively changing the leverage at the hand; cable actuation and travel would of course remain the same. Doesn't the shifter hub diameter remain the same regardless of grip diameter?

My, this gets the creative juices flowing...

Also a good observation relating actuation effort to pedal force. When I read that one has to momentarily ease off on pedaling pressure to shift, I figured it was to ease load on the internal components, including the shifting mechanism.

Best,

Dan.

rualexander

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #23 on: June 23, 2012, 08:48:40 PM »
The cable pull is 7.4mm per gear according to the page I linked to above, so if the cable 'spool' of the shifter is of a different diameter to the Rohloff version then the angles of rotation must be different to suit.

Danneaux

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #24 on: June 23, 2012, 09:05:11 PM »
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...if the cable 'spool' of the shifter is of a different diameter to the Rohloff version then the angles of rotation must be different to suit.
Got it; makes perfect sense, and reconciles what seemed to be two different approaches. Thanks!

Best,

Dan.

fleur

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #25 on: June 23, 2012, 10:58:53 PM »
What I am dreaming of is a bar end shifter for the Rohloff instead of the rotating grip. 

It should be possible to make a bar end shifter with two cables and the cables travel needed by the Rohloff.

All second sources also make rotating grips, there is one german company that announces a thumb shifter for the Rohloff but none makes a bar end shifter.

il padrone

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #26 on: June 24, 2012, 12:20:59 AM »
I think a conventional lever bar-end shifter for Rohloff is going to be a practical impossibility. The shifter rotates 270 degrees and the approximate diameter of the cable drum would be about 40mm. You wold be pushing to get 270 degrees of lever movement (if you did it would be very awkward operation) so this would demand an even larger cable drum. On your bar end this is going to be awfully clunky.

It is already quite feasible to have Rohloff shifting on the bar-end at present - yes it's clunky too  :-X





Dan, this design might be of interest in you desire to fit a shifter elsewhere on the bars. It's a much lower profile design.





Gilles Berthoud has also made a shifter that has somewhat different dimensions and can be slid right up along the bars around the bends to have a gripshift on the tops.




Perhaps this shifter is more your style Dan??  ;D



Mittelmeyer do a similar bar-mount one. They aso have been working on a design for a brifter-style for Rohloff. It's been 'in the pipeline' for quite some time and I think is currently due for release in September.

« Last Edit: June 24, 2012, 12:52:26 AM by il padrone »

fleur

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #27 on: June 24, 2012, 10:50:23 AM »
I think a conventional lever bar-end shifter for Rohloff is going to be a practical impossibility. The shifter rotates 270 degrees and the approximate diameter of the cable drum would be about 40mm. You wold be pushing to get 270 degrees of lever movement (if you did it would be very awkward operation) so this would demand an even larger cable drum. On your bar end this is going to be awfully clunky.

This is the difficulty of making a bar end shifter, the drum cannot be directly operated by the lever, there should be a demultiplication between the lever and the drum so that the drum turns a bigger angle than the lever.  When this is done, the cable can be rolled around the drum more than one turn and the drum turning more than 360 degree so that a smaller diameter drum can be used.

Seen how thin the Mittelmeyer thumb shifter is, I suspect there is a smaller drum that turn more than 360 degree in it.

il padrone

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #28 on: June 24, 2012, 11:57:31 AM »
This sounds like someone taking the simplicity of a hammer and making it more complex so the hammer will fit in their pocket. The Rohloff shifter is extremely simple with just a rotating barrel that two cables connect into. Adding extra leverage and connecting barrels will make it far more bulky, and more likely to fail in prolonged use.

For ideal drop-bar shifting maybe you need to go down this path ??

« Last Edit: June 24, 2012, 11:59:16 AM by il padrone »

fleur

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Re: Drop 'bars & Rohloff: A dozen differ'nt ways
« Reply #29 on: June 24, 2012, 12:58:06 PM »
Well, operating a rotating shifter on a drop bar always requires that you move your hands to reach it.  The "knob" that you show was made to be mounted on the frame and it has the same disadvantage that the Gilles Berthoud shifter that the cables and the drum are not protected from dirt, water...  I saw a picture of it installed on a bike and the cables were naked and under tension what is normally not good for the Rohloff.

I have also seen the electronic/electric shifter this is a nice solution but it is very bulky.  Seen what Shimano did on the Di2, it probably would be possible to make a very small electronic shifter but it requires big investments that Shimano and Campagnolo are able to do but impossible for a small company.