Mini-engine positioning on bicycle ?

Quoted message said:

Chalo Colina said:

Front hub motors are the easiest kind of kit to set up, but the best
ones to use are those which drive through the bike's gearing.
Examples
of those include the Cyclone kit (for single chainring derailleur bikes)
and Stokemonkey (for Xtracycle-equipped bikes). There are also
turn-key electric bikes like the Merida Powercycle and Giant LaFree
Lite that come with powered cranks rather than powered wheels.

Quoted message said:

http://www.cyclone-tw.com/

Ok, from here: 3rd world S.Africa I didn't get a proper download.
I'll try again later.
It seems to be DC 24V & 48V powered.
I'd like to know how they connect to the existing derailleur.

They are 24V kits. The 48V motor offered by the same company does not,
as far as I know, work with the same kit.

They don't connect to the derailleur. The Cyclone kit drives the
bike's own chain by means of a freewheel sitting just under and behind
the cranks. It's the same chain, shifted in the same way, as on any
derailleur-shifted bike.

Quoted message said:

What's 'single chainring' derailleur ?

The Cyclone kit comes furnished with a special freewheeled front
sprocket, so that the electric drive can function independently of the
pedals. Therefore there is only one ring in the front, and no shifting
can occur there. All the gear shifting must happen in the rear, with a
rear derailleur. Thus it's a single chainring bike with a derailleur,
as opposed to a single chainring bike with a gearhub or the like.

Chalo Colina

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OP said:

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Very few of them then drove the existing chain.
Now with the well developed 'multispeed gearing', it seems
obvious that the engine should use this existing mechanism.

1P said:

No, actually, it's not obvious at all.

I want the advantage of the existing gearing.
Except perhaps the speed would be dangerous, down even a
slight decline ?

Quoted message said:

The prevalent design of
derailleur gearing setup mandates that the cranks must turn
when the system is under power.

Yes. Do you need to have your legs stop 'turning' ?

Those of us who despise fixed-gear most certainly would, and with
motor assist, the cadence rate may overreach what the rider's legs can
tolerate. Add to that the pedal-snag factor; if the cranks must turn
all the time, then at some point you're going to find yourself needing
to be able to stop pedalling to pass a parking curb or other short
obstruction at just the moment that the rotation takes the pedal (and
your foot) directly into a collision course with the object. This is
a Bad Thing. In general, furthermore, you *do not* want any part of
your body being forcibly driven by something powered. The
opportunities for things to go wrong are many.

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What's more obvious is that an assist engine should have
a drive system that is as fully disengaged as possible when using
human power, so that the only penalty when pedalling is the extra
weight of the motor and system.

Yes, the motor 'declutches'.

Without a freewheel to allow the chain to stop, there's still
driveline drag from that extra chain, and it's not inconsiderable. It
also adds another set of clothing-snag issues.

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I believe this is best accomplished by the use of a special rear hub
equipped with a second freewheeling sprocket on the left side,
permitting the assist engine to drive the rear wheel independent
of and separate from the human-power system.

That's neat, expect my starting point is to use the existing gearing.
And you will have no variable gearing.

With appropriate choice of motor-system gearing, there should be no
need for multiple ratios. You originally proposed this as a part-time
assist device, not a main power system, and multiple gear ratios would
only be needed if the point was to achieve speeds that would not be
attainable under human power, or to use the motor to supply power at
lower speed when climbing hills. As you seem to envision it, this
isn't the best idea for a number of reasons. The simplest plan is the
safest; one ratio, separate drive systems, pedals not turning with the
engine engaged unless the rider wants to boost the speed, and a top
speed similar to what a rider can generate on a good day for a short
period. Trying to use multi-speed bicycle chain on a motor-driven
setup has its own set of problems; that chain's just too flimsy to
hold up under the strain of the impulses produced by an IC engine
that's capable of propelling the bike. So if you're really going to
use one chain for everything, you'd best plan to redesign the entire
system to utilize a heavier chain as well; say good-bye to
off-the-shelf derailleur hardware. Then add a freewheeling front
sprocket setup so the the cranks can stop while the motor drives the
chains. (Actually, a freewheeling front sprocket system has been made
for several uses, but I'm not aware of any current-production bikes
with them.)

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It would have to be clutched and probably geared down.

Centrifugal clutches are cheap and reliable. Gearing the engine
down is probably best done with a jackshaft.

What's a jackshaft ?

I suggest familiarizing yourself with the designs that have been used
for decades in go-karts and minibikes (and many other places) for gear
ratio matching. A jackshaft is, simply, a short shaft with two
different sizes of sprocket on it, used to match shaft speed
requirements when an overly large or small sprocket would otherwise be
required on one of the two ends of the drive system that the jackshaft
is in the middle of.

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Perhaps a belt-drive to do both ?

You're adding needless energy loss unless you want the belt to be
part of a variable-ratio drive system. Keep the speed and
grade-climbing parameters within a narrow (but still useful)
range, and you don't need it.

Is your 'jackshaft' better than a belt & pulley and can it 'declutch' ?

The jackshaft is just a shaft with two sprockets; properly
implemented, it imposes very little drag penalty. Belts have
hysteresis losses that are not a factor with chains.

Quoted message said:

Chalo Colina said:

Front hub motors are the easiest kind of kit to set up, but the best
ones to use are those which drive through the bike's gearing.
Examples
of those include the Cyclone kit (for single chainring derailleur bikes)
and Stokemonkey (for Xtracycle-equipped bikes). There are also
turn-key electric bikes like the Merida Powercycle and Giant LaFree
Lite that come with powered cranks rather than powered wheels.

Quoted message said:

http://www.cyclone-tw.com/

Ok, from here: 3rd world S.Africa I didn't get a proper download.
I'll try again later.
It seems to be DC 24V & 48V powered.
I'd like to know how they connect to the existing derailleur.
What's 'single chainring' derailleur ?

A bike with just a rear derailleur, and none in front. Using a
freewheeling double front sprocket set where the motor drives the
smaller sprocket of what would have been a front der setup, this
allows the motor to supply power through the normal gearing system.
I've seen it tried. The theory is good, but the execution generally
uncovers the same weak spots. Most important among them, derailleur
bike chain isn't really designed to bear the impulse load of an IC
motor. Electric power does not impose impulse loading; there, regular
3/32" bike chain often works just fine.

I would point out that the currently most successful off-the-shelf
motorization solution is very close to what I have advocated; the only
major design differences are the fact that it has a manual clutch and
that it does not add a second freewheeling sprocket on the rear wheel,
but rather uses a chain that runs whenver the bike is moving. This
adds a small amount of drag that a second freewheel would eliminate.
On the down side, those motorization systems have their share of
problems, mostly related to their low-budget design; the engines are
high-pollution 2-cycle units (which admittedly have a far higher
power-to-weight ratio and lower vibration than any common
similar-output 4-cycle motor), and the mounting systems are flimsy
and/or imprecise, among other things. I will admit that their design
does provide one advantage that mine would not; there is no need for
any kickstart lever, pull rope or electric starting motor, as the
always-running chain and the manual clutch allows starting the engine
by just engaging it. With either a centrifugal clutch or a freewheel
for the motor's chain at the rear wheel, this feature is lost. On the
whole, I would still prefer that the motor's chain not run with the
engine stopped, though.
--
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Werehatrack said:

With appropriate choice of motor-system gearing, there should be no
need for multiple ratios. You originally proposed this as a part-time
assist device, not a main power system, and multiple gear ratios would
only be needed if the point was to achieve speeds that would not be
attainable under human power, or to use the motor to supply power at
lower speed when climbing hills. As you seem to envision it, this
isn't the best idea for a number of reasons. The simplest plan is the
safest; one ratio, separate drive systems, pedals not turning with the
engine engaged unless the rider wants to boost the speed, and a top
speed similar to what a rider can generate on a good day for a short
period.

The central problem of power assist is the same as that of human power:
it is in short supply. Variable gearing helps make the most of a small
amount of available power, and when all else is equal, it is preferable
to a single ratio.

There can be advantages to a single ratio for an electric power assist.
If the gear is carefully chosen, it can provide sufficient torque for
hill climbing while tapering off to a low current draw at cruising
speed in order to conserve battery power or encourage maximum rider
input. The mechanical options are much simpler and more numerous if
one doesn't require variable ratio for the assist. And variable
gearing for the assist is easy to misuse, since shifting an electric
assist motor to deliver maximum power will usually result in poor
efficiency and range.

Of these, the only argument for a single gear ratio that seems to apply
to a gas motor is that of mechanical simplicity.

Chalo

Chalo said:

The central problem of power assist is the same as that of human power:
it is in short supply. Variable gearing helps make the most of a small
amount of available power, and when all else is equal, it is preferable
to a single ratio.

...the only argument for a single gear ratio that seems to apply
to a gas motor is that of mechanical simplicity.

Simplicity, weight and cost, actually, but I didn't mention weight and
cost in the original post because the subject of a motor/gearbox power
unit wasn't what had been posited. The OP had advocated using a, IC
motor driving a der system. I've seen this tried several times; it
self-destructs in short order. Electric drive through a der can be
done, but as you correctly pointed out, it's a poor plan. Electric
motors work best when they run at rated load and speed, and having the
der available would put the motor speed and loading out of the control
of the engineer and into the hands of the rider; range and motor life
reduction due to the rider's attempts to max out the motor's
capability would, as you posit, surely result.

I still hold that if a motorcycle is the desired result, then that's
what should be built; common bicycles are designed for human power,
and adapt poorly to having engines added. Power augmentation from a
battery and electric motor is more easily retrofitted, and far cleaner
as well. Its sole current disadvantage is lack of support in
infrastrucure; there's almost never a place to recharge at your
destination, so range is severely limited. Gas engines, although
nearly unlimited in range, have more adaptation problems, and with the
ones presently available, are high in pollution.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.