An all-automatic CVT based bicycle?

Andre Jute

On Jun 5, 6:16*am, bicycle_disciple <1.crazyboy.o...@gmail.com> wrote:

[Total snip, not because what went before is uninteresting but because
we're returning to even more interesting technicalities:}

> Andre ,
>
> I think you put that very well there. There is a segment of the
> consumer market which is composed of new people coming to bicycling.
> Most of them haven't ridden bikes before, leave along "serious biking"
> Some don't even know how to shift! The big question then is should
> bike companies impose bicycles that are already available and that
> which might not be necessarily optimum on this segment of consumers. I
> think its a nice idea to diversify as much as possible and capture
> everyone into cycling and bikes, whatever form it is...especially in
> these times of ridiculous energy prices.
>
> The challenge of this project however is different. The bike is to
> automatically shift based on an objective measurement of effort. My
> understanding is that one input alone, like cadence, is insufficient.
> I've written my thoughts already here :http://cozybeehive.blogspot.com/200...cvt-based-bicyc...

Shimano's Di2 system operating parameters are nowhere that is publicly
accessible described in detail or even completely in principle. The
most comprehensive description is on my netsite at
http://members.lycos.co.uk/fiultra/...0%20Smover.html
All the same, you cannot take what I say as gospel; some of that
material I hunted up from what is published, some I deduced or, to put
an engineering gloss on it, concluded from available material or daily
hands-on experience of the Di2 system over more than a year.

Conclusion from available material and experience with the hardware
and software: Shimano's Di2 system responds to six distinct operating
parameters and a couple of manual override modes:

-- intensity of light to switch on and off the lights; nothing to do
with changing the gears

-- motion; the front wheel must move to switch the system on and allow
operation; certain minor display and setting operations, and the
parameter sets, are protected by a small battery in the Flight Deck
(and possibly by either a charged up capacitor or a flash EPROM in the
CPU unit)

-- rider's desired power expenditure, read from an 8-position switch
the rider sets

-- velocity or speed of bike, measured by a sender in the front
dynohub

-- inclination of bike to change the setting of the electronic
suspension when climbing hills; I don't know whether this is also an
input to gear changing or whether gear changing depends solely on the
setting of the power switch and the speed measurement

-- operating map, one of three selected by rider via switch; this
controls how fast the gearbox ramps up the torque conversion; in the
most sporting of these maps bottom gear is locked out altogether

-- manual gearbox override, overrides other modes (maps) to permit
direct gear selection by up-down switch (actual gearchange still
effect by stepper motor as for auto change)

-- manual suspension override, permits firmness setting to be held and
changed by switch (in addition there is a mechanical preset and
lockout dial directly on top of the suspension fork, which performs
the same function for the suspension as the power switch performs for
the gearbox)

So, gear changes are definitely influenced by power setting, speed,
map setting, and possibly by inclination.
Notice that there is no connection to the bottom bracket or cranks. It
is however possible that torque is somehow read at hub and fed back to
the CPU as an input, but then why ask the rider to input a desired
power expenditure? On the whole I think power setting, speed and map
setting are all that is required for gearchanging in the Di2 system.

My experience is that this apparently simple system (compared to the
complicated system Steven Scharf is suggesting in his post) works with
incredible smoothness. My purpose in cycling is fitness, which I
define as endurance rather than bursts of power. Thus I regulate my
ride by putting my heart rate monitor on 80 per cent of max and simply
pedalling to keep it there under all road conditions (with a 15 per
cent max by time allowance for going over when tackling the steepest
hills on my familiar terrain say twice a week). I found that once I
discovered the right power setting, the Di2 system would always put me
in the right gear to hold my heart rate at 80pc of max up and down my
hills. There are no jerks; it is an almost imperceptible system,
which is why I say I cannot see the advantage of CVT unless it can be
made lighter (and weight is probably irrelevant to the small market
for automatic bikes).

> I have one question for you. You described the working of the Di2
> system. Now suppose I coast down on such a bike, my RPM is 0 in that
> case. Will the system make the mistake of upshifting?

The Di2 system manual talks about the system not working if you're not
pedalling but it measures nothing at the pedals, cranks or bottom
bracket, and I doubt it measures torque at the gearhub end. So RPM is
irrelevant. Whoever wrote the English manual just suffered a memory
glitch in which he forgot that the Di2 group isn't a cadence-
controlled racing gruppe. What happens is that according to power
setting, speed and selected mode (map) the CPU instructs the gearbox
to be in the correct gear for what you will do next; despite its
simplicity, it is a predictive system. If you're coasting fast
downhill, the gearbox remains in top gear; if you brake to a speed
where the best acceleration will be in a lower gear, the system will
change down to that gear. If you're coasting through a dip and the
speed falls as you coast up the next hill, the gearbox changes down so
that you are in the right gear to start pedalling at your
predetermined preferred power. If you're braking to a stop, the
gearbox changes down to the lowest gear permitted by the selected map
(first gear for maps D and L, second gear for map Ds). I've not in 14
months and about 2300 klicks caught out the Di2 system; Shimano got it
right.

> The di2 system is amazing. Previously, I had never heard about this.
> Perhaps is it because it is not available in the u.s?

Cyber Nexus is found on luxury Dutch city bikes, Swiss sporting bikes,
and bikes sold at a big premium by car companies like Daimler-Benz,
makers of Mercedes. The head of Kogo-Miyata said Cyber Nexus was her
vision of the bike of tomorrow; I don't know if Koga even lists a
Cyber Nexus bike any more; other luxury makers like Gazelle still
offer autobox-only Cyber Nexus models (without the fancy electronic
suspension) at a pretty good price but I don't imagine they sell all
that many. (Frankly, except for technofreaks like you'n'me, I'm not
sure there is a market; the Nexus manual gearchange is easy enough for
everyone, so an automatic gearbox is a solution in search of a non-
existent problem. There may be space for a cheap autobox at the other
end of the market, but beginners don't buy bikes in the Cyber Nexus/
Smover price class.) Even Trek, pretty wide awake marketers, made a
special line for the Cyber Nexus; Trek is now trying with automatic
bikes at a much lower part of the market. Like Citroen cars, it seems
likely that Cyber Nexus was considered too complicated for American
consumers and mechanics...

>I do not get the
> entire gist of what you're seeing, it'll be nice if there was a video
> to see it actually at work.

A video of me riding along, pedalling and doing nothing else, would be
dead boring. The point about Shimano's Di2 system is that there is
nothing visible or audible from the system, and the rider does nothing
except pedal and look around. That's what made Shimano's own video so
dull -- there was nothing for those interested in the engineering to
latch onto.

>Anyways, too much writing for today.
>
> BDhttp://cozybeehive.blogspot.com

HTH.

Andre Jute
http://members.lycos.co.uk/fiultra/...%20CYCLING.html