Gears

The donor bicycle had a Sachs Huret Commander hybrid derailleur and internal hub gear with 12 speeds (6x2). Note the bent rear rim, by the way.



The origins of this derailleur goes back to 1980, when Fichtel and Sachs bought the French bicycle component manufacturer Huret. They combined the 2-speed internal gear hub "Orbit" by Sachs with a Huret derailleur in versions of 5x2, 6x2 and 7x2.






This type of gear was popular during the 80s, specially for street bicycles with 28" wheels for urban transport. It was sold with the Sachs-Commander lever system for control, with two levers placed at hand in the handlebar, one controlling the internal gear hub and the other the derrailleur. The levers had defined steps with notches to engage, what was not common in the 80s, as friction levers was the usual. The very straightforward shifting and the reliable operation of this gear system contributed to the popularity among the general public of non-specialized cyclists.



Those of you willing to learn more about the history and technical features of this bicycle gear, are referred to the following sites:

http://www.disraeligears.co.uk/Site/Sachs-Huret_Commander_derailleur_-_instructions.html

http://www.karstilo.net/hpv/technik/sachs_sram/2gang/index.php

At the beginning I planned to recycle the Sachs-Huret Commander, as it fitted the requirements of this bike. I disassembled the wheel and took the internal hub apart. Luckily I found in the web the assembly schematics and the manuals. In the following pictures the disassembled hub can be seen.



It has 2 gears: High, or direct transmission through the engaging of the pawls in the central axis assembly with the ratchet mounted in the aluminium casing; and low gear with a ratio of 0,74:1 via 3 planetary gears and the sun gear machined in the central shaft.



I cleaned, greased and put the hub back together. It was in good working condition. On the other hand, I cleaned and oiled the derailleur and control levers.

However, one day I was talking to a colleage at work who is also interested in bicycle projects and he offered me a Sachs Pentasport 5 gear internal hub, as he had one in his cellar since long with no prospects of ever using it in his projects. Thanks, André!

At first you might think that this was not a good idea, as I would decrease the functionality from 12 speeds of the Sachs-Huret to only 5 speeds of the Pentasport. This, however, is not correct. The Sachs-Huret, was created by merging 2 existing products into one. The final result, was a gear system reliable and easy to operate in street bikes, but the spacing of the gears is not optimized, as the high and low ranges are largely superimposed. This means that not all 12 gears are of practical use, as many combinations are redundant. Morever, the most important feature is the range from maximum to minimum transmission ratio.

In the following table I compared three scenarios: Sachs-Huret Commander 6x2, Sachs Pentasport and a Sturmey Archer AW 3-speed (I have many of these around in my cellar).



You see that the Sachs Pentasport, with a more compact and modern design, covers the same range of transmission ratio from 3,3m to 7,5m per pedal revolution with only 5 speeds, commanded by a single trigger-type lever. The Sachs Huret has superimposed ratios in the ranges L4-L6 and H1-H4, so that there are only 8 meaningful transmission ratios that can be achieved. On top of that, the lower ratios L1-L4 are grouped very tight together, making some of them redundant. The Sturmey-Archer, on the other hand, could be confortably used only in gentle slopes as the lower ratio starts from 4m per pedal revolution. I expect this bicycle to climb slopes up to 8%. Then, the Pentasport is the best of the three options.


Here it is, the Pentasport internal gear hub, duriing the process of frame development after the design-as-you-go methodology.

Seat - Shaking the paradigm of equestrian saddles

The hammock seat constitutes the very essence of the Pedersen concept. This hammock saddle suspended from springs and belts to the rest of the frame structure eradicates forever that imaginary horse the cyclist is seating astride, thus shattering the paradigm derived from centuries of equestrian tradition. This configuration is very adaptable to the cyclist's anatomy and allows for lateral oscillations and tilting while pedaling or leaning sidewards.

The original Dursley Pedersen had a woven seat as seen below

At the beginning of the project I was considering weaving my own seat. In the following site there are very detailed instructions.

http://www.dursley-pedersen.net/weave.html

However, I finally decided on a more conventional and pragmatic solution, based on an old Brooks leather saddle.

I found an old and neglected Brooks B66, as you see in the picture below. Very classic and aristocratic looks. I can recycle it and with some rejuvenation to the leather part, it will fit perfectly the style of this bike.




The lower support structure and springs were disassembled. I kept, of course, the internal structure that stretches the leather part between the rear and front copper rivets. This structure and not the leather will be taking the stresses introduced by the anchoring points.



In order to fix the front to the head tube by means of a leather belt I need to manufacture a kind of bracket to hold the shackle. I used a 1.5 mm metal plate, that can be seen below.



Cutting, drilling, filing... All by hand. No power tools.



Bending a nice curl with the diameter for the shackle eye-bolt. I brazed the joint at the curl.



Here it is, assembled to the seat leather tensioning mechanism.



Note the internal seat structure and the springs attached to the rear part.



Another view of the seat assembly ready for mounting.



To attach the front shackle to the rest of the frame I am using a pair of old Swiss military belts from the 50s-60s. If they were originally used in backpacks or horses I can not say. But they are made out of very strong and seasoned leather and have the classic looks that fit with the style of this bike.
First view of how the bicycle looks like at the moment. It is not yet finished, not yet even ridable. However, it is taking shape. To connect the seat stays to the rear dropouts I used 3.5 mm steel cable passing through the tube at the extreme of the trombone's upper adjustable part. The positioning of the handlebars is not realistic. In such a position there would be interference with the knees and unconfortable wrist position. I just mounted all parts together for the first picture.