Re: An all-automatic CVT based bicycle?
bicycle_disciple wrote:
> Hi all!
>
> Question : Is it possible to remove handlebar shifting and make an
> automatic shifting bicycle with a Nuvinci hub? How is it possible? I
> tried to juggle with this a bit here :
> http://cozybeehive.blogspot.com/2008...d-bicycle.html
>
> I like the Nuvinci hub design. Its unique but I obviously never had
> one myself to try out. What are your thoughts when comparing this to
> previous CVT transmissions? Did anyone use it and have any problems in
> high torque, low speed situations? Thanks!
Shimano already turned their Nexus hub gears into an automatic gearbox
for bicycles. In the top model, called Cyber Nexus or Di2, the system
consists of the following:
-- Di2 8 speed gearbox, essentially same as Nexus 8sp Premium
(redline) and Alfine box
-- Stepper motor attached to box to perform actual gear changes
-- Computer unit to instruct stepper motor when to change
-- Special version of Flight Deck to act as control/infomation centre
-- A switch to select among several gearchange modes if desired
-- Hub dynamo to provide power for all units (the only battery in the
entire system is a is a small flat CR2032 hearing aid battery to keep
the presets alive in the Flight Deck)
In addition, Shimano's Di2 Groupset also includes
-- active front and rear suspension, under the control of the
computers and switches described above
An alternative version of the same system works with derailleur
equipped bikes with, IIRC, 27 speeds; it switches the derailleurs
rather than a hub gearbox but otherwise works much the same.
Shimano's Cyber Nexus/Di2/Smover system (Shimano uses all these names,
and a few others for the same components...) works very much in the
way that Joseph suggests you should turn your adaptation of the
NuVinci into an automatic gearbox.
First the rider chooses a level of exertion on a dial with 8 stops on
the CPU box; this is like, on a lesser bike, choosing a pedalling
cadence and specifying your crankwheels and cluster of sprockets
accordingly. Now the rider just gets on and pedals. Gears are changed
up for him when he speeds up, and down when he slows down. He can
additionally choose among four programmes (by switch, not by voice
command as Joseph wants -- it's bad enough talking to your computer in
private, but talking to your bike on the street is really weird!)
which are manual, Ds, D, and L. Manual is obvious: the gears switch up
and down as you instruct and the box stays in the gear you select. D
is the standard drive mode, fully automatic. Ds locks out the lowest
gear and changes up more quickly than D; it is the sporting mode of
the autobox. L is the leisure mode, and changes into an easy-pedalling
gear as sooner than D, and hangs on to easy pedaling gears as long as
it can. In all manual modes when you stop the computer changes the box
down to the lowest gear permitted in that mode, 1st for D and L, 2nd
for Ds. In other words, it is a fully automatic box, set and forget if
you want to, with additional very pleasing facilities if you want to
use them. In addition the active suspension works the opposite way to
that of a car: when you're going slowly it is set to hard to save all
your power for acceleration, ditto for going up hills; on the downhill
or going fast on the level the computer sets the suspension soft for
comfort.
I might point out that this entire Shimano Cyber Nexus system probably
weighs less than NuVinci hub. Thus, when you have added CPU and
control elements, plus dynohub to provide power, to the NuVinci, it
will weigh much more than the Shimano Cyber Nexus system, which shifts
imperceptibly and whose distinct intervals are around 14 per cent of
its range. CVT by itself is not enough to overcome all those
advantages that Shimano already has, including crucially the fact that
the Nexus 8 speed box is proven beyond any doubt, and the not
forgetting the monstrous benefit of Shimano's history of making
fabulous parts cheaply. Furthermore, Shimano has their target market
right in the crosshairs: their Cyber Nexus system takes clean, fully
enclosed, roller brakes, entirely suited to sort of monied rider who
doesn't llike getting his hands, or his clothes, oily. By contrast the
NuVinci designers are under some kind of a misapprehension that
sporting riders will buy a CVT gearbox, otherwise why did they make
the thing take a disc brake?
Personally, I think that the NuVinci will be gone in a couple of
years; its first makers have already failed and sold out. Shimano,
selling a lighter system built on the solid foundation of proven, even
loved, components, and at a very keen price, couldn't create a mass
market, or even a large niche market for an automatic bike in the
obvious place, at the top of the market for city and credit card
touring bikes; the evidence for this is that there are now very few of
the Cyber Nexus bikes listed out of even the few that were made, and
Shimano is trying again at the very bottom of the pile with, for
instance, the Trek Lime. If Shimano, who have a lot of marketing nous
and clout, couldn't do it, Johnny-come=latelies with only a single
mousetrap to their name, and a poor grasp of the motives of users of
mousetraps (as I have already proved), are most unlikely to last the
course.
However. If you are really so much in love with CVT that you want to
spend your time and pocket-money trying to make the NuVinci automatic,
you could start with the pretty inexpensive (for what they are)
Shimano Cyber Nexus parts already well designed to to the job. You
would need the CPU, the control switch, the Flight Deck, some cables,
and a source of power which had better be the Cyber Nexus specific
dynohub which already has a speed sensor built in which responds to
the CPU, and the stepper unit. The immediate job will be adapt the
stepper unit to switching the NuVinci box; if that fails, get a linear
or rotary stepper unit and attach it to the cable itself and try to
make the Shimano CPU control it. Once you can make the stepper unit
move the CVT box in seven discrete steps (for eight speeds as in the
Nexus 8, because that's what the hardware you're adapting is set up
for), then it will be time to spend some time learning programming so
as to work with the flash ROM inside the CPU to see if you can
programme a continuously variable response to torque input.
HTH.
You can see my own Cyber Nexus automatic bike at
http://members.lycos.co.uk/fiultra/B...%20Smover.html
and about halfway down the page is a clear photo of all the elements
required to make an automatic gearbox work on a bicycle.
Andre Jute
http://members.lycos.co.uk/fiultra/B...20CYCLING.html
