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Old 04-04-09, 10:31 PM   #1
callagga
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Question does going faster than max speed create drag for a hub motor

Hi,

On an electric bike with a hub motor (e.g. Crystalyte 408 series), after one passes the point when motor torque drops to zero (http://www.ebikes.ca/simulator/ - e.g 35km/hr for 408 series at 36V) does the electric motor then start causing some friction/drag as the rides uses additional pedal power to go faster?

For example if you freewheeling down a hill and pass this point does the motor start offering up some drag?
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Old 04-05-09, 09:36 AM   #2
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I don't think it matters what speed you are going, you are going to get 'drag' from a direct drive hub motor when you are not applying electricity to it.
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Old 04-05-09, 05:34 PM   #3
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Quote:
Originally Posted by callagga View Post
Hi,

On an electric bike with a hub motor (e.g. Crystalyte 408 series), after one passes the point when motor torque drops to zero (http://www.ebikes.ca/simulator/ - e.g 35km/hr for 408 series at 36V) does the electric motor then start causing some friction/drag as the rides uses additional pedal power to go faster?

For example if you freewheeling down a hill and pass this point does the motor start offering up some drag?
Based on the way that you have worded the question.....No, there is no hockey stick response to the drag from your motor.

However, the previous poster is correct when he says that a direct drive motor creates drag on your system.

I suspect, that the amount of drag will not be a concern for you. I hope that helps.
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Old 04-06-09, 02:07 PM   #4
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Quote:
Originally Posted by callagga View Post
Hi,

On an electric bike with a hub motor (e.g. Crystalyte 408 series), after one passes the point when motor torque drops to zero (http://www.ebikes.ca/simulator/ - e.g 35km/hr for 408 series at 36V) does the electric motor then start causing some friction/drag as the rides uses additional pedal power to go faster?

For example if you freewheeling down a hill and pass this point does the motor start offering up some drag?
Well, if the power is not on, you'll always be slower than a regular bike because of the inherent motor drag.

If the power is on assisting, then I would say yes, there is a speed at which it'll be easier on your legs to just coast downhill on a regular bike rather than to add speed to an electric motor.
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Old 04-06-09, 03:25 PM   #5
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does the electric motor then start causing some friction/drag as the rides uses additional pedal power to go faster?
Yes, but if you're NOT racing it's probably not enough to matter.

Edit: added the word "not". OOPS.

Last edited by cerewa; 04-10-09 at 06:20 AM.
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Old 04-09-09, 08:46 AM   #6
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My brushed hub motor cruises 22-24mph but I frequently go 28-31 down hill w/o any noticable drag.
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Old 04-09-09, 08:48 AM   #7
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At higher speed, wind drag will be MUCH more of a problem.
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Old 04-10-09, 06:02 AM   #8
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I tested the drag yesterday going down a hill that is steep enough so that the coasting speed is faster than the hub motor can normally propel it to on flat ground. I am not using a regen controller.

I did it at full throttle and then at no throttle--switch turned to off.

The drag was the exact same.

I've drawn the conclusion that after one passes the point when motor torque drops to zero, the rider would have to pedal hard enough to overcome the drag from cogging. At that speed and with that much drag, it would be a very difficult thing to do in order to maintain cadence for more than a few seconds at a time.
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Old 04-11-09, 01:38 AM   #9
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If the motor is programmmed to shut off at a particular speed, you will get drag. It's the same as if you pedal with the motor turned off, since the motor turns off when hitting certain speeds. The magnets drag on the wheel when the motor is off, regardless of why it is off.

Mine turns of at 20 mph. I've actually hit 21 mph while going down a hill with plenty of acceleration behind me. But it's all gravity and acceleration overcoming the drag at that point. Without the motor, I'd probably be going a lot faster down that particular hill. Then again, without the motor, I wouldn't be able to accelerate that much to begin with.
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