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Old 04-23-2012, 11:04 AM   #6 (permalink)
jkv357
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Quote:
Originally Posted by bennelson View Post
Why would you question a single-speed gear reduction? It's been done on TONS of EVs, both cars and cycles. (Ever wonder how a Tesla Roadster works? It's just a single gear.)
He's right to question it. Motors don't make power efficiently at all RPMs. Especially if you have a limited power output (battery) your peak efficiency is important. They will make torque from 0 RPMs, but will draw a ton of power to do it. Peak revs are also limited, and efficiency drops off quickly, so you do run out of stream.

The Tesla runs fast 0-60, but performance drops off quickly at higher speeds.

2-speed or CVT would help a lot.

My son is working on an EV right now for a high school competition, and is working with a single gear. We are gearing for a peak speed (45 MPH) based on the max RPM of the motor (3200RPM @ 36V). But when starting from a stop or climbing a hill he will use a bunch of power to pull that gear. Better would be to have a low and high gear to conserve power. A CVT would let you run the motor at it's peak efficiency the entire time while altering gearing. That's a bit past this project though.


Jay
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