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11-20-07, 10:59 AM
#5
cerewa

Join Date: Jun 2003
Location: southeast pennsylvania
Posts: 3,155

Bikes: a mountain bike with a cargo box on the back and aero bars on the front. an old well-worn dahon folding bike

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I'm curious about how that works as well. I see all these ads saying how much farther it can go if you do some pedaling. But when you pedal are you dragging the motor and batteries or is it making the motor go faster?

When you pedal, the bike either goes faster or uses less power. Say you have a bike that goes about 15mph on flat ground at a power level of 250 watts. If the motor puts out 250 watts the bike goes that speed, but the bike also goes the same speed if you put out 125 watts and the motor puts out 125 watts. (you'll get double the distance for the same amount of battery power.)
If the motor puts out 250W and you put out 125W then your speed will go up a few miles per hour.

Essentially, Pengyou, a hybrid (pedal-electric or any other combination) can be made to take full advantage of all of its power sources at the same time and it doesn't matter too much whether one power source is a tenth as strong as another or whether they're equal, etc. - whatever number of watts the motor transmits to the wheel, PLUS whatever wattage the pedals transmit to the wheel, is what will determine how fast you go.

But in order for your ebike to take advantage of pedaling the pedal-gearing has to be right. Regardless of the speed of the bike, your ideal pedaling speed when you want to put out a moderate amount of effort is something like 90 revolutions per minute. If your effort level stays exactly the same, then your efficiency probably goes down to 0% at 120rpm (most of your effort is used up just moving your legs around, none of it helps the wheels move).

You could design a bike instead to be a multi-speed bike which takes advantage of pedaling at about 90rpm anywhere between 6mph and 35mph, which would allow you to put out maybe 200W of power at any of those speeds. You could have a motor which was also able to put out 500W or more through that entire range. This bike would be just as fast as a bike with a motor operating at 700W (power output) but no pedals, but the bike without pedals would need better batteries.