Please post future off the topic of EVT America Z-20a and Z-20b replies about the Xtreme XM-2000 here.
The two-speed set up of the XM2000 just seems like an unnecessary feature. One of the advantages of DC electric motors is that for a given voltage input, they only produce more torque the slower they are going.
On the XM, it is unknown if the shifter is shifting gears, enacting different windings, or some other method which, if known in detail, may be found to be far more desirable/undesirable than simply altering the voltage.
(A) To address the desirableness of the feature: One advantage that can be seen is that the low speed setting does stress the batteries less for 0 to 20 mph acceleration - even when accelerating at the same rate. This is indicated by seeing less voltage drop when using low speed. Therefore, I'd say that it is a worthwhile feature.
(B) To address the torque characteristics: There are many different types of DC motors (series and shunt being just two) - they have different torque characteristics - so PJD's comment although true seems a little broad to apply to this situation. As usatracy points out we need to know much more about (a) the nature of the motor windings & (b) the nature of the shifting mechanism to figure anything more out in theory. However, in practice see (A) - it is worthwhile for me.
FWIW, my guess is that it's enacting different windings. I'm sure usatracy will take his motor apart soon ;-)
Ann Arbor, MIhttp://www.revevllc.com
John H. Founder of Current Motor Company - opinions on this site belong to me; not to my employerRemember: " 'lectric for local. diesel for distance" - JTH, Amp Bros || "No Gas.
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