Most powerful eBike for long uphill journeys?

[soundwave]

then you are about 18% fitter than EddiePJ.
With a CD torque multiplier system, the faster you can drain the battery, the fitter you are.

in turbo i get about 5 miles per bar of 5 total on the flat so add in climbing and distance and speed eddie goes 2 x the distance but i go 2 times as fast and get about the same batt usage.

id win a 28 mile race id lose a 35 mile one imo

 

[Zlatan]

D

in turbo i get about 5 miles per bar of 5 total on the flat so add in climbing and distance and speed eddie goes 2 x the distance but i go 2 times as fast and get about the same batt usage.

id win a 28 mile race id lose a 35 mile one imo

Cant imagine Eddie running a dongle though...

 

[GLJoe]

You should take a close look at EddiePJ's run from Lauterbrunnen to Wengen to see how powerful the CX motor is and how hard you have to work to squeeze the last pip out of it.

You are missing the point.
I am not denying that at the higher speeds, the system does require you to put in significant wattage yourself.
What I am saying, is that from observation, you can change down, keep the cadence up, DRASTICALLY reduce your own input power, yet STILL get the Bosch motor to max out the power meter and you progress up steep hills with very minimal rider input, albeit at a reduced speed. I haven't worked out the exact details of what's going on here, but I and others have noted it happening in real world use.

 

[Zlatan]

You are missing the point.
I am not denying that at the higher speeds, the system does require you to put in significant wattage yourself.
What I am saying, is that from observation, you can change down, keep the cadence up, DRASTICALLY reduce your own input power, yet STILL get the Bosch motor to max out the power meter and you progress up steep hills with very minimal rider input, albeit at a reduced speed. I haven't worked out the exact details of what's going on here, but I and others have noted it happening in real world use.

I totally agree with that. You explained it better than I could, perhaps others never need to resort to this to get home. I often do. ( Mine is Yamaha tho, but noticed very similar )

 

[Woosh]

You are missing the point.
I am not denying that at the higher speeds, the system does require you to put in significant wattage yourself.
What I am saying, is that from observation, you can change down, keep the cadence up, DRASTICALLY reduce your own input power, yet STILL get the Bosch motor to max out the power meter and you progress up steep hills with very minimal rider input, albeit at a reduced speed. I haven't worked out the exact details of what's going on here, but I and others have noted it happening in real world use.

I understood what you said, you change the way you input your power by changing gear and pedaling faster.
But that doesn't change the assist ratio between user input and motor output.

That is the important point. The system still gives you the same assist ratio.
In turbo, that's *3. If you pedal faster, it's still *3, not *4 or *5.

 

[soundwave]

what you want is one of these

 

[chris_n]

I totally agree with that. You explained it better than I could, perhaps others never need to resort to this to get home. I often do. ( Mine is Yamaha tho, but noticed very similar )

Doesn't make sense to me, if you are maxing the power on the meter then how is it helping you get home? Surely (and I do have a lot of experience of this) you change to a lower gear and a lower assist level to keep the power meter down to increase range.
I know that in my experience if you try and keep a Yamaha PW motor at high crank rpm it makes no power, it's my biggest criticism of it. Having said that what I regard as fast cadence may not be the same as you. I also have no experience of the Bosch motor.

 

[Deleted member 4366]

All crank motors have a power band. After a certain pedal speed, the power ramps down due to the back emf, so you have to be careful about pedalling too fast if you want a lot of assistance. It's not the control system that does that. it's just the way electric motors work.

 

[GLJoe]

I understood what you said, you change the way you input your power by changing gear and pedaling faster.
But that doesn't change the assist ratio between user input and motor output.

That is the important point. The system still gives you the same assist ratio.
In turbo, that's *3. If you pedal faster, it's still *3, not *4 or *5.

If what you say is correct, then what is happening is that I am observing an overall system response, without fully understanding all the interrelationships between cadence, power, gravity, wind drag etc etc. And I concede that might indeed be the case.
However, are you 100%. And I mean 100%, positive, that the assist ratio never, ever goes above 3 ? (in a Bosch or Yamaha system)

 

[anotherkiwi]

All crank motors have a power band. After a certain pedal speed, the power ramps down due to the back emf, so you have to be careful about pedalling too fast if you want a lot of assistance. It's not the control system that does that. it's just the way electric motors work.

Thanks for that! I have been fighting with this issue for a while. So I must have a natural cadence over 86 rpm - probably in the mid 90s. Time to get a 44 tooth chainwheel?

 

[Woosh]

However, are you 100%. And I mean 100%, positive, that the assist ratio never, ever goes above 3 ? (in a Bosch or Yamaha system)

as much as I can be from what I have seen and read, yes.

 

[Deleted member 4366]

Thanks for that! I have been fighting with this issue for a while. So I must have a natural cadence over 86 rpm - probably in the mid 90s. Time to get a 44 tooth chainwheel?

Or increase the voltage. Going from 36v to 48v would shift the power-band up by 33%, so if ideal cadence was say 65 RPM, it would then be 86 RPM. On the other hand, if you've maxed out along with the motor, a bigger chainwheel would be the solution.

 

[GLJoe]

Thanks for that! I have been fighting with this issue for a while. So I must have a natural cadence over 86 rpm - probably in the mid 90s. Time to get a 44 tooth chainwheel?

Someone posted a very useful graph a week or so ago, showing the power band of the various common commercial motors. If someone can remember the link, it would be very useful.
The Yamaha was lower than the Bosch, however it still have a fairly useful range IIRC.

 

[GLJoe]

as much as I can be from what I have seen and read, yes.

Ok, I can see I need to think about this some more.
Another question then.
What does this multiplier actually multiply? We call it them torque sensing systems. Is is just reacting to how hard you press on the pedals? or is it actually a power multiplier? because isn't power = torque * RPM (or cadence) ?? and if so, wouldn't that be the reason why you would have to measure the cadence as well as the pedal torque ???

 

[Woosh]

What does this multiplier actually multiply? We call it them torque sensing systems. Is is just reacting to how hard you press on the pedals? or is it actually a power multiplier? because isn't power = torque * RPM (or cadence) ?? and if so, wouldn't that be the reason why you would have to measure the cadence as well as the pedal torque ???

torque multiplier = power multiplier because power = torque * rotational speed as you already said.
You and the motor turn the same chain wheel, therefore bound to the same rotational speed so the function can be simplied to just assist ratio = motor's torque / rider's torque. The cadence is useful to prevent false start (you press on one pedal while the other foot is still on the ground). The torque value is fast moving, the rotational speed less so, the system uses both to average out the assist.

 

[anotherkiwi]

Or increase the voltage. Going from 36v to 48v would shift the power-band up by 33%, so if ideal cadence was say 65 RPM, it would then be 86 RPM. On the other hand, if you've maxed out along with the motor, a bigger chainwheel would be the solution.

For quite some time I have been thinking of moving up to 44.4 V 12S which for me is a sweet spot in the voltage range, increase of 23% rather than 33%. Should work with a 36 V controller if LVC is raised in the C12 setting of the LCD-3.

This really only affects me when climbing not so steep hills at just under the cut off speed, very annoying when your motor cuts out just when you need it. The standard 46 chainwheel is just a little too big with 28" wheels and my current 42 tooth just a little too small. The much easier solution of course is to set cut off speed to 30 km/h, or not set it...

 

[GLJoe]

The system works as a torque multiplier.
when you shift down a gear, eg from 26T to 24T, you decrease the ratio front to rear by 8%, the motor increases your cadence by 8% as a result, reduces the required torque for you by 8%........ You always get the most out of the motor when climbing in the lowest gear and while keeping the cadence as high as possible.
The thing to remember is the system works on rider's input power, that is torque times angular speed, you get twice as much out of the motor if you spin the pedals twice as fast.
.

I'm still trying to get my head around this

isn't there a contradiction in the post above.
"the system works as a torque multipler" and indeed people talk about needing to push hard on the pedals to get maximum motor power.
But then then it describes to 'get the most from the motor' you increase the cadence, to REDUCE the torque, and the system works on 'the riders input power'.
So that indicates its a power multiplier, not a torque multiplier ? or am I missing something?

And I'm still confused by one basic observation. I know that when I'm gunning it, I have to work pretty hard to keep the bikes in built power meter maxed out and I probably wouldn't be able to keep that effort up for long. But going up a steep hill (slowly) in a low gear and keeping a good cadence, the power meter can still be maxed out, yet it feels as if I could sustain that effort forever. Surely I am therefore inputting significantly less power/torque. How can the power meter be maxed out in both conditions?

 

[Deleted member 4366]

I'm not sure, but I'd say that your power meter is displaying motor current. That's what most do. Voltage is constant, so that's also proportional to the power from the battery. Torque is more or less proportional to current, so that means that the display could be interpreted as motor current, torque or power from the battery.

The power from the battery isn't proportional to the motor's power because, motor power depends on two things: mainly it's speed, but also its efficiency, which varies with speed.

Adding that all together, you'll get maximum power from the motor at about 75% of it's maximum RPM. Maximum torque would be available, probably in the range 0 to 70% of maximum RPM if you can press the pedals hard enough. It's probable that the controller's algorithms aren't as simple as current being directly proportional to pedal torque. It's probably closer to that at low RPM with a bit of smoothing added, but as cadence increases, they bring in other factors, bearing in mind that after a certain RPM, maybe 70, the motor self-limits the current more and more as the speed increases. The control system cannot increase it above that no matter what you do.

Each time you change gear, the motor speed changes, and the gearing affects the torque at the back wheel. You have to take that into consideration too.

 

[Woosh]

Someone posted a very useful graph a week or so ago, showing the power band of the various common commercial motors. If someone can remember the link, it would be very useful.

here you go:

http://pedelecs.co.uk/forum/threads/still-not-to-sure-what-to-make-of-bosch-ebike-system.28008/#post-378429

see how good the CX is.
That thread caused me to prepare a bike to compete with the CX next year.

 

[Zlatan]

Correct me by all means DV but isn't motor torque with respect to rpm just,about a flat line until max rpm ? ( thought it was one of advantages over ICE engines who,s torque curves can be all over place)

Totally agree re once some ( as yet unknown) cadence is hit motor cant give any torque..( ie motor is at its max rpm)
Don't think I have ability to reach that cadence tho ...