Hub
motors are inherently heavier and bulkier than gear driven wheels. And they are worthless for hill climbing unless they are mounted like these are.
This is the right place for a hub motor
but a second drive chain is needed. cheaper to build your own. |
To run only the axle there is a complex operation https://endless-sphere.com/forums/viewtopic.php?f=28&t=45245 |
There
is a new Stoke-Monkey G02 with internal gear reduction, but I don't know
if it is a 5 to 1 ratio or what. In this chart you can see that if
you make a 1.6 to 1 gear reduction to a 26” wheel it may do the
job.
A
12” wheel is a gear reduction of 2.16 to 1, of a 26” wheel
(tire). So this gear reduction would equal about 10½
mph on the 26” wheel. With this reduction ratio it is possible to
drive a little faster if you're willing to gamble the motor over
heating. Or you can build a smaller ratio reduction like 1.7
to 1 for about 12-13mph (always count on less output)
E.
Hub
motors should be rated by how much torque they can produce rather
than how many watts they can produce,
It
is not the motor power that causes a motor to overheat, but the motor
torque. To avoid this problem, use a larger motor or a higher voltage
for a higher RPM. At
a higher RPM a given motor can produce more power.
High
voltage with a low amperage will keep the motor from over heating.
But of course you need a larger gear reduction. To build it in a
single stage you will need a large pulley on the drive wheel.
Possibly a 12inch rim
pulley
custom made with epoxy teeth molded to fit the timing belt that will
be long and wide enough. Although a two stage reduction maybe better
it would be more expensive to build.
This
chart shows that a 2.705
to 1 ratio of my 23 inch drive wheel at 72volts and 25 amps will make
high enough rpms to keep the motor from over heating.
Read this for more info: MOTOR POWER RATINGS
Smaller
drive wheels are like using a lower gear. But it is hard to find a
cargo bike with a 16” wheel. Mounting the hub motor in the center
will let you build a lower gear. You may need an even lower gear for
a steeper hill.
You
can see that it is hard to find a hub motor that will drive you up a
9% grade with 440lbs (200kg; total combined weight) at any speed with
a one-to-one ratio with out using way too much power. (as direct
drive hub motors do).
Higher
voltage with a custom controller
Using
higher voltage will be like using a lower gear because it allows more
wattage without increasing the amperage (higher amperage requires
thicker wires), but then you have to increase the gear ratio even
more because the motor will be moving faster at that higher voltage.
If
you have a 26 inch drive wheel and steep hills to climb, trade your
bike for a long tail cargo bike with a 20 inch drive wheel.
Start
with a 'geared' hub-motor
with a 5 to 1 ratio and if that is not enough, you will need to build
an external gear reduction.
Very
few hub motor can use 88volts with out a special operation. And so I
say forget the hub motors and buy a mid drive then drive the rear
wheel directly, not through the bikes pedal powered chain, to save
the chain and sprockets from wearing out too fast.
Pay
close attention to the Motor Power Curve (Red Line) and the Black
Curve (Load Line). Typically the Motor power curve will rise up in an
arc, and then abruptly fall off on a straight line down to "0"
The highest point (Apex) of the motor power curve is when the motor
is demanding the full current output of the controller (and where it
is least efficient).
If
the Load line intersects to the right of the apex of the motor power
curve, then the controller is powerful enough for the system. If the
load line intersect the motor power curve to the left of the apex of
the motor power curve, then the controller is too small, and we
should look for a more powerful (higher current) controller.
The
black Load Line shows the power required to propel the configured
bike at any speed. This has nothing to do with the simulator - it
reflects the same results you get from any standard bike speed
calculator - basic physics - nothing to do with motors. This is all
about aero drag, rolling coefficient, grade, etc.
The red
line is the mechanical power the motor can deliver at any speed
where speed varies according to load not throttle. This is based on
dyno data and Justin's modeling - this is the 'simulation' part and
has nothing to do with drag, grade, etc.
The intersection
of these two lines is the point where the power to propel the
bike is exactly equal
to the power produced by the motor. This indicates the
terminal speed for that bike configuration and load. This is simply
a graphic solution to two separate sets of power equations (i.e. it
could be done algebraically - the graphic solution is equally
valid...)
This
means that if you want know how much power it takes to push your bike
to 35mph, you just turn off all the lines except the Load Line,
configure the bike, then look at the power at 35mph... This is the
amount of power required regardless of the motor or drive system.
It's only when you play this curve against a specific motor that you
get into the terminal speed, etc where the specifics of that
motor/battery/controller can be balanced against the requirements of
the bike/grade/etc.
For
example, in the plot above, we see that it takes about 3200W (motor
power) to push that bike to 45mph. Using the same efficiency as shown
(86.9%) we see that although it takes about 2680W (battery power) to
achieve 40mph, it would require 3200/.869 = 3680W (battery power) to
get to 45mph - a fairly staggering increase for 5mph - but perfectly
understandable when you look at the steepness of the Load Line at
that speed.
Motor simulator graphs:
Converting a hub motor to a middrive motor
eBike school:
Gear reduction from a hubmotor:
do not put a hub motor on the front wheel! |
Vector
Control does not add horse power, it can only move it to when and
where you need it. Such as when you need extra thrust, like climbing
steep hills with cargo or starting off from a dead stop at a traffic
light.
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