Does a motor keep providing assist even when it exceeds its winding speed?

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Lovelock   1 W

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Does a motor keep providing assist even when it exceeds its winding speed?

Post by Lovelock » Sep 18 2018 10:30am

I'm running a Q128c (36v 201rpm) at 48v and get 22mph as its top speed but wondering what happens when I pedal faster than that?

If going downhill at 22mph+ the throttle will not provide any assist and the display shows no watts being used, but, what happens if I'm on a flat ride and pedaling with PAS at 25mph.

Will the motor still make this speed easier and provide assist once it goes past the windings top speed? I feel like it doesn't when riding, but wondering if its even worth pedalling after 22mph at all if I'm looking for an easy ride.

Thanks.

Punx0r   10 GW

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Re: Does a motor keep providing assist even when it exceeds its winding speed?

Post by Punx0r » Sep 23 2018 4:30am

If it's a direct drive motor it will act as a progressively worsening brake as you exceed it's no-load speed.

If it's a geared motor (which I think yours is?) they usually have a clutch/freewheel and should disconnect if driven beyond no load speed and you should be able to pedal or coast like a regular bicycle.

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Chalo   100 GW

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Re: Does a motor keep providing assist even when it exceeds its winding speed?

Post by Chalo » Sep 23 2018 4:13pm

Punx0r is exactly right, but I'll add one point of clarification. 22mph is your motor-only top speed, but it's lower than the no-load speed of the motor. Above 22mph and below the no-load speed (whatever that is), the motor will continue to contribute power, but at a steeply declining rate as the speed increases. When the no-load speed is reached, the motor will no longer add anything to your pedal power.
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Re: Does a motor keep providing assist even when it exceeds its winding speed?

Post by Lovelock » Sep 24 2018 3:53am

Chalo wrote:
Sep 23 2018 4:13pm
Punx0r is exactly right, but I'll add one point of clarification. 22mph is your motor-only top speed, but it's lower than the no-load speed of the motor. Above 22mph and below the no-load speed (whatever that is), the motor will continue to contribute power, but at a steeply declining rate as the speed increases. When the no-load speed is reached, the motor will no longer add anything to your pedal power.
Thanks for clarifying.

No load speed is rear wheel off floor right? That gives me the same 22mph, I must not be very heavy :D

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Chalo   100 GW

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Re: Does a motor keep providing assist even when it exceeds its winding speed?

Post by Chalo » Sep 24 2018 4:08am

Lovelock wrote:
Sep 24 2018 3:53am
No load speed is rear wheel off floor right? That gives me the same 22mph, I must not be very heavy :D
There may be some kind of electronic speed limiting. If your system has a setting for wheel size, change the entered wheel size to a different one and see if the indicated top speed (wheel off the floor) remains the same. If so, something is intervening to limit the top speed.
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Re: Does a motor keep providing assist even when it exceeds its winding speed?

Post by dogman dan » Sep 26 2018 8:16am

Chalo explained it perfect. But if there is a rpm limiter built into the controller, it will then turn off power at that 22 mph speed. So freewheeling or not, whatever the no load of motor may be, the system is at least lowering the power at 22 mph.

The best way to really find out is to put a watt meter between your battery and your motor. When its showing about 5w its not running the motor, its just keeping the display and controller lit up. The wattmeter will show you when the motor is at no load, or when a limiter kicks on.


Watt meters are really fun, in addition to what the motor is doing, they can show you what you contribute. Example, ride 15 mph pedaling, then stop pedaling. The difference in watts is approximately what your pedaling contributed. The number is not really accurate, (Because the motor and controller wastes some watts) but it does give a number you can compare to other speeds, or levels of effort. Repeat the experiment with varying effort. You can see motor only takes 200 w to go 15 mph or whatever, then turn off the motor and see what keeping up that speed feels like. With experience, you can learn what that feels like in pedal pressure on your foot. Now you can judge your personal output on any bike, at any time. For me, I needed to keep my effort below 75w, because of an illness I have. So at any speed, I tried to aim for that much effort, judged by the pedal feel, my rate of breathing, etc. Under 75w, no limit to the distance, over it, I would get sick quickly.

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Re: Does a motor keep providing assist even when it exceeds its winding speed?

Post by Lovelock » Sep 26 2018 10:10am

dogman dan wrote:
Sep 26 2018 8:16am
Chalo explained it perfect. But if there is a rpm limiter built into the controller, it will then turn off power at that 22 mph speed. So freewheeling or not, whatever the no load of motor may be, the system is at least lowering the power at 22 mph.

The best way to really find out is to put a watt meter between your battery and your motor. When its showing about 5w its not running the motor, its just keeping the display and controller lit up. The wattmeter will show you when the motor is at no load, or when a limiter kicks on.


Watt meters are really fun, in addition to what the motor is doing, they can show you what you contribute. Example, ride 15 mph pedaling, then stop pedaling. The difference in watts is approximately what your pedaling contributed. The number is not really accurate, (Because the motor and controller wastes some watts) but it does give a number you can compare to other speeds, or levels of effort. Repeat the experiment with varying effort. You can see motor only takes 200 w to go 15 mph or whatever, then turn off the motor and see what keeping up that speed feels like. With experience, you can learn what that feels like in pedal pressure on your foot. Now you can judge your personal output on any bike, at any time. For me, I needed to keep my effort below 75w, because of an illness I have. So at any speed, I tried to aim for that much effort, judged by the pedal feel, my rate of breathing, etc. Under 75w, no limit to the distance, over it, I would get sick quickly.
Thanks for adding more to the reply.

I'm using a q128c, the LCD3 display shows 0w when over 22mph. If I lift the bike off the floor and use the throttle the max speed still shows 22mph, the same as the top speed when just using the throttle on the road.

I was just curious, 22mph is the winding limit of the motor so it makes sense. 201rpm 36v but overvolated to 48v.

It might just a psuedo effect, but I was cycling around 25mph yesterday and felt like it was easier than without a motor.

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