Having over 1300 miles on the PMG-132 in a light(er) bike aprox. 440lbs and a <200lb rider I find the heat generated in the motor to be controllable with the small fans and shroud I made. Where am I going with this, oh yeah. If I were trying to build a bike based on a heavier frame I would opt for a larger motor, like a D&D or if you have deeper pockets one of the smaller Warps or a custom motor from JH versus a dual Etek or Dual PMG (2 PMGs will set you back roughly $1600 so why not do the series wound and have the thermal mass to handle the required power dissipation under acceleration).
Jeff On Mon, May 5, 2008 at 8:04 AM, SteveS <[EMAIL PROTECTED]> wrote: > 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 > > > > ------------------------------------------------------------------------ > > Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it > now. > <http://us.rd.yahoo.com/evt=51733/*http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ%20> > > ------------------------------------------------------------------------ > > > > No virus found in this incoming message. > > Checked by AVG. Version: 7.5.524 / Virus Database: 269.23.8/1415 - Release > Date: 5/5/2008 6:01 AM > > > > > > > >
