Feedback with mid drive motors, heavy bike and Nexus (7)

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Plortus   10 µW

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Feedback with mid drive motors, heavy bike and Nexus (7)

Post by Plortus » Jan 24 2022 7:58am

Hello,

This is my first post here. I hope I will follow the rules of this forum :).

I am considering upgrading my Genesis Smithfield with a mid drive motor.
It's a heavy bike (28kg - 61.73 Lb) and it has Nexus 7 hub.

My typical trip is 10km with 120m elevation gain (6.2 miles - 394 ft).
On the way there, I don't want to sweat at all because I'll meet clients.
There are many stops on the way (traffic lights, roundabouts, etc.). So I'll have a lot of stops and starts.

I have a lot of concerns:
With pedaling sensors (Bafang):
1. Would I need a gear sensor for smooth shifting and no damage to the hub?
2. Can the stops and starts wear the hub? If yes, how to prevent that?

With torque sensors (Tonghsheng):
3. Does it work well without a gear sensor?
4. Will the assist be strong to avoid sweating at all?

Many thanks for your feedbacks.

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spinningmagnets   100 GW

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Re: Feedback with mid drive motors, heavy bike and Nexus (7)

Post by spinningmagnets » Jan 24 2022 8:22am

When pedaling a bicycle with no motor, I always stopped pedaling to shift, and then gently ramp up power when pedaling resumes. That seems to provide a smooth gear-shift.

Ive found that using that technique with ebikes works well too. Some drive types and gear shifters may tolerate more abuse than others, but I don't know what issues would occur with a Nexus-7.

Ebikes have a 5V e-brake circuit, so that when the brakes are applied, the power is cut. The "gear sensors" use a hall sensor next to a magnet on the shift-cable to sense movement, and it cuts power for a moment to reduce shock to the gear-shifting.

Plortus   10 µW

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Re: Feedback with mid drive motors, heavy bike and Nexus (7)

Post by Plortus » Jan 24 2022 9:23am

Hello spinningmagnets,
Thank you for your answer.
Regarding gear-shift, I'd like to be sure, we have the same thing in mind:
When I shift, I just release the pressure on the pedals so that there is no effort on the transmission when the shifting occurs.
I mean I don't completely stop pedaling, I just slow down.
Would you say this is enough with an e-bike? Or would you have to literally stop pedaling (no movement at all), then shift, then start pedaling again?

Atm, I would prefer the Bafang over the Tongsheng regarding my "no sweat" constraint and the ability to adjust the power map to preserve the Nexus 7?
But I'd like to keep enjoying pedaling my bike specifically regarding gear-shifts...

AHicks   10 kW

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Re: Feedback with mid drive motors, heavy bike and Nexus (7)

Post by AHicks » Jan 24 2022 9:38am

To build on what spinningmagnets is saying (I think), is many of us are used to shifting multi geared bikes prior to riding our first e-bikes. We're already used to that pause in effort required for a smooth shift. It's a habit most don't even think about. That same habit works just as well when shifting an e-bike.

The shift sensor doesn't change a thing for me. About 90+% of the time I shift, it's pausing at exactly the same time I am. To the point you don't notice it's even there. Other times, maybe when your timing is off a bit, you'll notice it. Big thing in my mind is there is no downside to having one installed.

If shifting is new to you, or it's something you haven't done a lot of, I believe a sensor should be a welcome addition to your rig.

Plortus   10 µW

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Re: Feedback with mid drive motors, heavy bike and Nexus (7)

Post by Plortus » Jan 24 2022 4:33pm

Hi AHicks,
Yes I'm also used to that "pause of effort" during shifting. I used to ride a mountain bike on single tracks with 2000m elevation gain. Good shifting skill is mandatory on those steep tracks ;).
So it's great to hear that the same habit will have the same effect, I mean smooth shifting. I was wondering if I can save the extra money without risking to break the Nexus.

Regarding the Bafang vs Tongsheng stuff, would you have something to add?
Thanks!

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Chalo   100 GW

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Re: Feedback with mid drive motors, heavy bike and Nexus (7)

Post by Chalo » Jan 24 2022 5:50pm

I would be very cautious about putting superhuman power through a Nexus 7. 750W if you're not pedaling in earnest, less if you want to jam on it. Don't use especially low gearing on the chain drive.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Plortus   10 µW

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Re: Feedback with mid drive motors, heavy bike and Nexus (7)

Post by Plortus » Jan 25 2022 6:14am

Hi Chalo,
Thank you for your feedback.

At the moment I'm planning to use a 250W motor or maybe a 500W.
I read that installing a big chain ring with a small sprocket is a good practice to protect a speed hub like the Nexus.
What do you think?

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Chalo   100 GW

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Re: Feedback with mid drive motors, heavy bike and Nexus (7)

Post by Chalo » Jan 25 2022 7:51am

Plortus wrote:
Jan 25 2022 6:14am
At the moment I'm planning to use a 250W motor or maybe a 500W.
I read that installing a big chain ring with a small sprocket is a good practice to protect a speed hub like the Nexus.
What do you think?
That power range should be no problem.

Raising the external gear ratio is a good idea, as long as your lowest gear is still low enough to ride the bike without power in your local conditions. Raising the ratio (with a larger chainring or a smaller rear sprocket) not only reduces the maximum input torque to the hub, but it allows you to pedal the bike along with the motor at higher road speeds than you would otherwise be able to.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

Plortus   10 µW

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Re: Feedback with mid drive motors, heavy bike and Nexus (7)

Post by Plortus » Jan 25 2022 8:44am

Thanks again for you answer.
That's very enlightening for me :).
I should be able to increase the gear ratio a bit and still be able to ride my bike without the help from the motor.
Anyway, I'll keep that in mind.

Braddudya   100 mW

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Re: Feedback with mid drive motors, heavy bike and Nexus (7)

Post by Braddudya » Mar 01 2022 11:27am

I have a rather heavy bike with a BBS02 and a 13ah 48V battery. It is very easy to avoid breaking a sweat. Its a simple system to install and it just works. For shifting I have found I can just touch the brakes (enough to trip the sensor but not enough to actually engage the brakes) and quite easily shift. You can also get a shift sensor but I have no experience with it.

One of the best parts with the BBS02 is that is it nearly completely silent.

I think you would be very satisfied with this kit.

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