[confused] Torque sensor, gear ratio, pedal assist

[Jeremy McCreary]

that’s what i’m wondering about - is the reaction to the motor torque also in the dropout where the TMM4 is located?

I wondered that too. But if it were, seems like that would really complicate the controller's assist power calculation.

 

[mschwett]

I wondered that too. But if it were, seems like that would really complicate the controller's assist power calculation.

that’s why i was wondering if you could just adjust for / subtract the known power being sent to the motor. but of course the efficiency varies by speed, and at some point it all gets fussy enough that nobody would bother !

i do know that on some eBikes, the power readings for “rider power” become more inaccurate as motor power goes up.

 

[Jeremy McCreary]

that’s why i was wondering if you could just adjust for / subtract the known power being sent to the motor. but of course the efficiency varies by speed, and at some point it all gets fussy enough that nobody would bother !

i do know that on some eBikes, the power readings for “rider power” become more inaccurate as motor power goes up.

Yes, I think we're squarely in "who would bother" territory here. A very high-end manufacturer?

A motor-specific controller with a complete motor model in memory — including the efficiency-speed, mechanical power-speed, and torque-speed curves — could do some interesting things. But doing all the math might take a faster, more powerful processor, more onboard memory, more sophisticated programming, and more rigorous testing. And all that takes money.

 

[Jeremy McCreary]

that’s what i’m wondering about - is the reaction to the motor torque also in the dropout where the TMM4 is located?

In thinking about this more, the left end of the rear axle is clamped directly to the frame, while the right end is clamped to a TMM4 clamped to the frame. If the axle is strong enough to resist torsion by the motor, the TMM4 might be pretty isolated from the actions of the motor.

 

[Jacko]

Welcome aboard!

I have a geared hub motor with well-implemented torque-sensing assist. Guessing that the following is largely true on mid-drives as well...

I have a very strong preference for a cadence of 85±5 RPM. To maintain that cadence on a given grade, I can choose a lower gear with lower assist level or a higher gear with more assist. The difference: In the latter case, I'll be going faster.

So to go substantially faster at constant cadence and grade, I upshift and increase assist at the same time. When the grade increases, I tend to maintain cadence first by downshifting, letting speed drop as it may. If speed gets too low in bottom gear, I start upping assist to maintain cadence.

Nothing magic about this — just an example based on the way I like to ride. I can monitor cadence and ground speed on my displays, but the gear/assist changes are usually just done by feel.

Having a 10-speed cassette and 9 assist levels makes it easy to dial in the combo of cadence, exertion, and speed I'm after at any given moment without thinking about it. For better or worse, I give ZERO thought to motor speed and efficiency, but I have plenty of battery for the riding I do.

Someone please correct me if the game is substantially different on a mid-drive.

Your riding style and your choice of bike seem almost identical to mine. I ride a Bagi bike with Bafang 500w hub with a 9 level PAS controller. I bought on trial a Evelo Aurora mid motor with manual CVT hub. Did not like it at all. Couldn't find a sweet spot to save my soul. Sticking with the cadence hub drive. Mine however is only "cadence" scening no torque. Would I like one like your bike better??

 

[Jeremy McCreary]

Your riding style and your choice of bike seem almost identical to mine. I ride a Bagi bike with Bafang 500w hub with a 9 level PAS controller. I bought on trial a Evelo Aurora mid motor with manual CVT hub. Did not like it at all. Couldn't find a sweet spot to save my soul. Sticking with the cadence hub drive. Mine however is only "cadence" scening no torque. Would I like one like your bike better??

Can't say. All I can do is relate my own experience...

I've ridden 7 different hub-drives, all 500 W. Never a mid-drive. The first 5 were cadence-sensing, and all 5 felt off to us, some more than others.

Then we tested No. 6, my current torque-sensing ebike. And we both thought, OK, that's the way to do pedal assist! Very natural ride feel. Rode them another 20 min to be sure, then bought 2 then and there. Each was $500 over budget, but no regrets.

(I'd been an avid cyclist in younger years, wife had ridden little as an adult, but we had similar reactions to all 6 test rides. So it wasn't subtle.)

A year later, got a chance to ride a torque-sensing Aventon Level.2. Specs are very similar to my Rook's. Ditto for the ride feel. So my Rook's probably not a fluke. And after 2,000 mi now, I really appreciate having an assist system that 's not limited to 2 motor power levels — 0 and 100%.

HOWEVER, some members really like their cadence-sensing bikes. And I gather that some cadence-sensing and torque-sensing implementations are better than others.

Moreover, I live in a place crawling with ebikes ridden mainly for transportation. And the vast majority of those are cadence-sensing. (Think Rad Rovers and Super73s.) A lot of them were probably purchased before reasonably priced torque-sensing bikes came on the market. But for these utility riders with little interest in pedaling — and nothing wrong with that — cadence-sensing makes some sense.

 

[Jacko]

Can't say. All I can do is relate my own experience...

I've ridden 7 different hub-drives, all 500 W. Never a mid-drive. The first 5 were cadence-sensing, and all 5 felt off to us, some more than others.

Then we tested No. 6, my current torque-sensing ebike. And we both thought, OK, that's the way to do pedal assist! Very natural ride feel. Rode them another 20 min to be sure, then bought 2 then and there. Each was $500 over budget, but no regrets.

(I'd been an avid cyclist in younger years, wife had ridden little as an adult, but we had similar reactions to all 6 test rides. So it wasn't subtle.)

A year later, got a chance to ride a torque-sensing Aventon Level.2. Specs are very similar to my Rook's. Ditto for the ride feel. So my Rook's probably not a fluke. And after 2,000 mi now, I really appreciate having an assist system that 's not limited to 2 motor power levels — 0 and 100%.

HOWEVER, some members really like their cadence-sensing bikes. And I gather that some cadence-sensing and torque-sensing implementations are better than others.

Moreover, I live in a place crawling with ebikes ridden mainly for transportation. And the vast majority of those are cadence-sensing. (Think Rad Rovers and Super73s.) A lot of them were probably purchased before reasonably priced torque-sensing bikes came on the market. But for these utility riders with little interest in pedaling — and nothing wrong with that — cadence-sensing makes some sense.

Thanks Jeremy... I was an avid cyclist also (73yr old now) had heart trouble at 50 and was unable to ride for years until the E-bike. Wow I tell you just being out on a bike again is heaven. Im going to try a torque sensing bike to see difference, I will have to wait awhile however I live in Wisconsin! I will let you know my experience.

 

[Jeremy McCreary]

Wow I tell you just being out on a bike again is heaven.

Couldn't agree more! Huge boost to overall wellness. And in my hilly area and state of fitness at the time, it wouldn't have been possible without an ebike. Our generally good bike infrastructure also helped.

Good luck with your purchase.

 

[MikeDee]

Why do you need a torque sensor with a hub motor system? I ride an Orbea Gain with an X35 system and it works just fine. Pretty seamless. If I want more power, I just push the button to go up another assistance level. What am I missing?

 

[Jeremy McCreary]

Why do you need a torque sensor with a hub motor system? I ride an Orbea Gain with an X35 system and it works just fine. Pretty seamless. If I want more power, I just push the button to go up another assistance level. What am I missing?

Motor placement and the sensor types used to dole out assist power are largely separate engineering decisions.

A quick internet search on the X35 hub motor turned up no quick answers on the assist sensors used. Do you know for sure that it doesn’t use a torque sensor somewhere in the system — perhaps one hidden in the drive hub?

 

[MikeDee]

Motor placement and the sensor types used to dole out assist power are largely separate engineering decisions.

A quick internet search on the X35 hub motor turned up no quick answers on the assist sensors used. Do you know for sure that it doesn’t use a torque sensor somewhere in the system — perhaps one hidden in the drive hub?

It only has a PAS sensor at the hub (a magnet ring built into the cassette lock ring and a sensor in the right dropout) which only detects whether you are pedaling or not.

 

[Jeremy McCreary]

It only has a PAS sensor at the hub (a magnet ring built into the cassette lock ring and a sensor in the right dropout) which only detects whether your pedaling or not.

Interesting. Perhaps Mahle's found a way to add some sophistication to the simple pedal or cassette rotation detection used in most "cadence-sensing" ebikes.

All I can tell you is summed up in post #46 above. And we're not alone in finding a stark difference in the riding experience between torque-sensing and simple cadence-sensing hub-drives. Guess you'll have to try both kinds to see for yourself.

The forum search function may also help.