Electric Bikes - (near) zero friction/drag motor assist, does it exist?
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05-09-09, 02:58 PM
Iíve been a bike commuter, up to now I've had a shower at work. This allowed me to travel in bike cloths, shower and change before going to my desk.
I'll be in a new office soon with no shower available. I would like to ride to the office in the morning without working up a heavy sweat by using an electric assist bike.
I would then like to cycle home under human power to get some needed exercise.
Does the mechanical friction or the magnetic field of the electric motor create substantial drag when not in use?
On my Estelle (Heinzmann front hub) I can't tell because the bike is so heavy to begin with. So, I'm going to say not much, probably the same as a dyno hub.
On my Giant Twist (Panasonic BB drive) there is some noticeable drag, say about the same as a bottle generator.
Look at the cyclone direct chain drive. I don't believe it creates any drag at all.
The cyclone motor freewheels when not in use (i.e. the motor doesn't turn while the bike's chain and wheels turn). The extra turn in the chain to accomodate the motor's gear will lose you a tiny, tiny amount of energy.
Geared hub motors (like the "bafang" hub motor) will probably create even less drag - all that's added is a freewheel mechanism inside the wheel.
The thing is, even a gearless hub motor (higher drag because the motor spins whenever the bike rolls) doesn't have much effect. Mind you, the extra weight of batteries and motor does make a difference whenever you accelerate or climb a hill.
If you want a workout in the evening, you could just consider the extra drag part of your strength training (and making up for the easy morning) or if you don't think you can handle that, use the motor but only use it on your steepest hill or when you're sure you can't continue on pedal power.
05-10-09, 06:05 AM
I have a BMC geared brushless rear hub. It completely freewheels. No drag whatsoever & it is supposed to be the among lightest available.
I have a front geared brushless hub fitted into my existing bike. Freewheel.
I often feel there's a little friction when taking my thumb off the throttle and pedal. Must be psychological, as I was "pull along" by the motor a moment before.
However, at one time, I wasn't able to use my electric motor for a week (warranty repair on my charger ) , used the bike unassisted and I didn't notice the friction at all.
Warning: In practice, I find myself using the motor rather than pedalling uphill no matter how easy the hill is. My heart rate doesn't increase much. . . . . But my intention is good though :o
05-10-09, 01:12 PM
Thanks everyone. My commute is flat, so a heavy bike is not a serious issue. I was afraid that I would be driving a generator when the motor was not powered. I don't mind some extra effort, but I did not want a slow commuter over 15 miles. I now see that this is not the case.
05-12-09, 04:43 PM
The Currie motors on Schwinn Izips or the Walmart ones that have a separate chain do not drag at all. In fact when I first bought mine I had no battery for a week and went on 20 mile trips with no power, it felt like a regular bike.
05-13-09, 07:04 AM
All the options above have integrated freewheels somewhere in the system.
I have a Heinzmann brushed hubs on my ebikes and it has a integrated freewheel so it is drag free
if you are going faster than the motor.
The direct drive hub motors will have some drag, which people sometimes call coging.
Yes, see the thread below:
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