I get the idea of the two motor system, but how does compare to using a
larger single motor? I imagine a single larger motor would be easier to
install and control. The larger motor would deal with the low speed
torque need, but I wonder about what happens when you get up to speed?
Would a larger motor be less efficient?
- SteveS
dale henderson wrote:
The advantage of a transmission is more power at low speeds while at
the same time reducing the power needed. But once you are up to a
cruising speed the transmission does not any help except for allowing
the motors to operate at high efficiency at more than one speed. The
disadvantages of a transmission are increased drag, or lower overall
efficiency and increased weight.
The advantage of a two motor system is that a second motor is often,
if not always, lighter, smaller, simpler and more efficient than a
transmission. The disadvantage of a two motor system is increased
power requirement.
Here is another way to look at it: if your main concern is high
efficiency at a particular cursing speed [e.g. highway travel] then
longer you travel the less efficient a transmission becomes and
conversely the more efficient a two motor system becomes. A
transmission only increases efficiency during acceleration once you
are at a steady speed the transmission reduces efficiency in terms of
drag and weight. While a two motor system is only less efficient
during acceleration, so if you have little acceleration and a lot of
steady speed then two motor system is overall more efficient.
Here is a very simple model; if it gives good results then a closer
examination would be warranted: take a 25-mile highway trip, we’ll
give a ¼ mile acceleration; more simply a 100-mile trip with 1-mile
acceleration. At any give time the motorcycle needs X power. A
transmission is 5% less efficient than a non-transmission so over 100
miles it will take 100 miles * .05 = 5 units more power. The two motor
system will take twice the power at acceleration 1 mile * 2 = 2 units
more power. But if you are commuting in stop and go traffic then a
40-mile commute might have over a 1 of acceleration. So a transmission
is 40 * .05 = 2 units and a two motor system is still 2 units. So if
your steady speed is more 40 times longer than your acceleration then
a two motor system is more efficient. But if your steady speed is less
40 times more than acceleration then a transmission is more efficient.
A closer study is needed and results will vary based on
rider/bike/weight/route/etc… but I think it will be clear that in
short city travel a transmission is more efficient, but in longer
highway travel a two motor system is more efficient. But since an
electric motorcycle has a finite range and can’t be filled up at the
pump then it should be built to be the most efficient for the
longest-range option. Hence once you get an electric bike going over
50 miles on a charge [i.e. lithium] and you have some plans to travel
on the highway then a two motor system is the best choice. Further
with a 100+ mile range, city travel never be a concern, even with the
lower efficiency of the two motor system, but when a long trip on the
highway is needed the two motor system will shine as it will give you
more range than a transmission.
harry
Albuquerque, NM
http://www.austinev.org/evalbum/1179
http://geocities.com/solarcookingman
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