Thinking of converting my commuting bike - questions and advice

[pajtaz]

Ok. If I don't use a speed sensor but only a cadence sensor, how will the motor know (I guess the controller) at which what speed I am going? When will it cut off? It must be based on something else.

I am trying to compare torque and cadence sensors and trying to understand how I can achieve speeds higher than I am capable by using hub motor. I thought motor will assist until it reaches some power limit and not speed. So I thought motor will keep providing power but based on how much pedaling I am doing. Maybe different controllers do things differently?

 

[sjpt]

Usually cadence sensor bikes (and torque ones too?) have an additional speed sensor mounted on one of the wheels ... exactly like the standalone speed sensors you can buy for a tenner or so except they feed into the rest of the electric system.

You can sometimes cheat these by telling the display lies about the wheel size; eg if you have a 27" wheel and tell it its 20" it will register 15 mph when you are really doing about 20mph. Doesn't make the 20mph assist legal though.

 

[vfr400]

The controller can get a speed signal from either the motor hall sensors or a speed sensor. Some motors have internal speed sensors otherwise you can fit one to the wheel.

Independently from the controller, every motor has its own maximum speed, so it's important that you choose one with the speed you want. They normally list them by RPM, e.g. 201 rpm is 15 mph, 260 rpm is about 20 mph and 328 is around 25 mph. Those speeds are in 26" wheels and at nominal battery voltage. Speed is proportional to voltage, so you get about 10% more than that with a fully charged battery. Also, they're the speed at which the motor runs out of power, and the power ramps down before that, so you're on-the-road speed is about 15% lower.

 

[pajtaz]

Now I get it. Thank you very much for all the answers. Using either torque and cadence sensor will not make a difference on when the motor cuts off. Difference is how the motor is controlled using torque sensor as input vs cadence sensor, where cadence senor is on/off and does not change the assist level set by the controller.

When the motor cuts off is at what I need to look when selecting a motor which will help me get to 33 km/h or whatever speed I want.

I was just hoping that motor was not using speed as input but only the available power based on my pedaling. Meaning, if I pedaled more, there would be more power available in the motor so I could go faster than if I was not pedaling or pedaling less. I guess that is not the case and every motor will be limited by speed. At this point it is up to me on what kind of assistance I want, whereas cadence sensor is much cheaper and can possibly fit on my current crankset or BB, and for torque sensor I need to change the BB and crankset.

 

[vfr400]

You're nearly there. With a cadence sensor, you set the amount of power on the controller's control panel (LCD, LED panel). There are mostly 5 levels with LCD and 3 with LED. If you don't get a control panel, you're correct that you only get max power when you pedal, which can be a bit inconvenient.

Now you can see that if you want a nice control system, it's worth spending a bit more to get a decent controller and LCD. Kunteng (KT) recommended.

For riding on the road and trails, a torque sensor system doesn't really offer any advantage, though is much better for serious off-road riding. That's comparing one with a decent cadence system, not the cheaper speed control based ones.

 

[Woosh]

I was just hoping that motor was not using speed as input but only the available power based on my pedaling. Meaning, if I pedaled more, there would be more power available in the motor so I could go faster than if I was not pedaling or pedaling less.

That may make sense in some context but impractical in reality. If you start off from 0mph, you will appreciate a burst of acceleration from 0mph. If the power were to increase with the cadence, you would get very little power at startup.

Our bikes and kits use Lishui controllers with 5 assist levels. They are spaced out as a percentage of assist power, 17A is the maximum, so you get a fixed percentage of the 17A at each assist level. Some LCD we use like the KD58C lets you program the percentage of power at each level, I usually set them to 40%, 60%, 75%,85% and 100%. The assist will go up to the preset power level but whichever assist level you are at, the controller acts in such a way that you have to pedal a bit to maintain the speed.

For example, you are on assist level 3, the maximum power is 36V * 17A * 75% = 459W. The controller won't give out all of that when you are on a flat road but would if you climb a steep hill.
Let's assume you pedal leisurely at 10mph on a flat road at assist evel 3. The power required if roughly 75W. The controller would supply about 50W and you put in 25W. Then you start climbing a steep 10% hill at the same 10mph, the power required is roughly 500W, you can put in 80W and the motor 420W. If you want to climb faster than 10mph, you will have to either push the throttle to maximum or increase assist level. The throttle will always have precedence over pedal assist setting.
The main difference between a modern cadence system and a torque system is essentially you have to pedal all the time and harder on hills with a torque sensor.

 

[Nealh]

KT controllers are a lot more frugal in there lower assist levels but are no way sluggish barring maybe PAS 1, there % current settings PAS1 - PAS5 are 13%, 20%, 33%, 50% & 100%.

 

[Nosweat]

For riding on the road and trails, a torque sensor system doesn't really offer any advantage, though is much better for serious off-road riding. That's comparing one with a decent cadence system, not the cheaper speed control based ones.

What's the difference experienced by someone riding a bike with a "cheap speed based cadence sensor" and a "decent cadence system"? Surely all cadence sensors have the same two inputs, (1) are you turning the pedals (however slowly) and (2) what level have you set the controller to? As an example, when I test rode a well-known brand bike recently that had a cadence sensor (I didn't like it), if I set the power level on maximum, as long as I was turning the pedals, even very slowly, the bike whizzed along at say 10mph on flat ground. If I pedalled fast enough that I was no longer "windmilling" or "ghost pedalling" and started to feel pressure, I could go faster if I wanted. If I set the power level to medium, the same would happen only I'd get whisked along at say 5mpg on the flat. Inch forwards very slowly with maximum assistance like I might do in heavy traffic and the bike would suddenly have a mind of its own and shoot forwards. Most disconcerting I thought, and I could understand why torque sensors are better. Unless you can advise me of different types of cadence sensors?

Just wondering with a torque sensor though - if I'm going up a gentle hill would I get more motor assistance (and therefore be able to go faster with less effort) by remaining in a higher gear (as my feet would be turning more slowly but with more effort), than if I approached the hill at the same speed but in a lower gear with faster cadence?

 

[Woosh]

Just wondering with a torque sensor though - if I'm going up a gentle hill would I get more motor assistance (and therefore be able to go faster with less effort) by remaining in a higher gear (as my feet would be turning more slowly but with more effort), than if I approached the hill at the same speed but in a lower gear with faster cadence?

no, just the opposite. Torque sensored bikes like high cadence. It's much, much easier to climb a hill at over 80 RPM than lower.

 

[Nealh]

The cheap ones tend to have speed control only so you get max current in each PAS level (might be 3 pas or 5PAS) with each PAS level having a max terminal assist speed, max current all the time eats in to battery capacity so you can't control the range as well and provides a less leisurely ride from start.

The KT's give you a choice you can choose between speed control or current control, the current supplied is (approx.) as I mentioned earlier. Apart from PAS1 you will get max speed in all the PAS levels and choose how much current/torque you need to apply given the terrain ahead. Tbh high current is only needed for ascents or for riders who haven't much stamina, if you need a blip of power then the throttle can deliver this (note throttle configured for pedal first for legality post 2016).
With speed control mode you will get 100% current all the time giving less control of power esp at times when not needed. If tootling along at 10/12mph you don't need 100% current unless you want max acceleration/torque constantly.

 

[vfr400]

KT controllers are a lot more frugal in there lower assist levels but are no way sluggish barring maybe PAS 1, there % current settings PAS1 - PAS5 are 13%, 20%, 33%, 50% & 100%.

Did you see the additional settings in C5? I never noticed them before. There's no explanation in the manual about what this means. Maximum current value is the amps written on the label. C5 cuts that down on values 3 to 9 and allows it without the slow start on value 10. These three values allow the max current subject to this slow start procedure, whatever it is. Maybe it's to stop it from jerking off on level 5 or when you give full throttle.
C5=0 Three level slow start/ Maximum current value
C5=1 Two level slow start/ Maximum current value
C5=2 One level slow start/ Maximum current value

 

[Nealh]

None of my current controllers have that option so must be a new setting on later/new firmware versions.

 

[vfr400]

None of my current controllers have that option so must be a new setting on later/new firmware versions.

I saw it in the LCD4 manual, but when I checked, it's also in the 2017 LCD3 manual.

 

[pajtaz]

I have been doing research. Based on your responses, considering my wants in my first post, and considering what is actually possible to buy, I have narrowed down the selections for motor. Can you please let me know if I am understanding everything correctly, do my selections make sense, and if anyone has experience with some of these motors.

1. Since I want to ride at 30 to 35 km/h, it seems MXUS XF08C at 250W and 36V is not adequate for me. Is this correct?
2. It also seems that probably any motor at 500W and 48V (and labelled as 328 RPM?) is too much for me because I will not be riding it efficiently. That seems to narrow down selections to 36V 350W motors or 48V 350W motors or motor labelled 48V 500W 201 RPM. Does that make sense?
3. MXUS has a motor that is interesting, can be purchased cheaply as part of a kit, and seems to be in stock on Aliexpress. MXUS XF15C. Does anybody know anything about this motor, reliability, noise, can it run with sine wave controllers like S12S? It comes in 36V or 48V and 350W and 500W options. Which one?
4. Only available Q128C is on BMSbattery and it is motor only with options of 36V or 48V and 201 RPM or 328 RPM. Which one of these would be the best for my situation and how difficult/expensive is it to get a bike shop to build a wheel around it? None of the other Q motors are available for purchase as kits or just a wheel, anywhere so this would be the only option.
5. Finally, there are a bunch of Bafang CSTs with various options on Aliexpress, again 36V or 48V and 350W or 500W. Which one?
6. For all of the above, which controller? I am assuming there is no need to go with 20A or higher controllers but maybe max of 15A? Sine wave controller with LCD3 or LCD4? This would rule out S12S because of its high current, is that correct? What other controller then?
7. Same for battery, look for a 36V or 48V battery with maximum discharge current of 15A? Or only focus on 48V batteries?

It seems I can also buy MXUS kits directly from MXUS on alibaba.com and they seem to allow option of purchasing just 1. Did anybody order from them directly and with low quantity?

So what do you think? Can anyone help out with above questions? Thank you again for all the help so far and all of the information.

 

[Nealh]

I have been doing research. Based on your responses, considering my wants in my first post, and considering what is actually possible to buy, I have narrowed down the selections for motor. Can you please let me know if I am understanding everything correctly, do my selections make sense, and if anyone has experience with some of these motors.

1. Since I want to ride at 30 to 35 km/h, it seems MXUS XF08C at 250W and 36V is not adequate for me. Is this correct?
2. It also seems that probably any motor at 500W and 48V (and labelled as 328 RPM?) is too much for me because I will not be riding it efficiently. That seems to narrow down selections to 36V 350W motors or 48V 350W motors or motor labelled 48V 500W 201 RPM. Does that make sense?
3. MXUS has a motor that is interesting, can be purchased cheaply as part of a kit, and seems to be in stock on Aliexpress. MXUS XF15C. Does anybody know anything about this motor, reliability, noise, can it run with sine wave controllers like S12S? It comes in 36V or 48V and 350W and 500W options. Which one?
4. Only available Q128C is on BMSbattery and it is motor only with options of 36V or 48V and 201 RPM or 328 RPM. Which one of these would be the best for my situation and how difficult/expensive is it to get a bike shop to build a wheel around it? None of the other Q motors are available for purchase as kits or just a wheel, anywhere so this would be the only option.
5. Finally, there are a bunch of Bafang CSTs with various options on Aliexpress, again 36V or 48V and 350W or 500W. Which one?
6. For all of the above, which controller? I am assuming there is no need to go with 20A or higher controllers but maybe max of 15A? Sine wave controller with LCD3 or LCD4? This would rule out S12S because of its high current, is that correct? What other controller then?
7. Same for battery, look for a 36V or 48V battery with maximum discharge current of 15A? Or only focus on 48V batteries?

It seems I can also buy MXUS kits directly from MXUS on alibaba.com and they seem to allow option of purchasing just 1. Did anybody order from them directly and with low quantity?

So what do you think? Can anyone help out with above questions? Thank you again for all the help so far and all of the information.

Start a new thread so as not to hijack someone else's, then we can make suggestions for your needs.

 

[pajtaz]

This is my thread. I am the one who started it. I can start a new one but I will have to repeat what I wrote in first post about my bike, how I ride, budget, etc.

 

[soundwave]

Kalk | CAKE

Light, quiet and clean. CAKE develops uncompromising high-performance electric motorbikes.

ridecake.com

 

[Nealh]

This is my thread. I am the one who started it. I can start a new one but I will have to repeat what I wrote in first post about my bike, how I ride, budget, etc.

Yes it is ………
I very rarely go back to the beginning to check.

 

[Nealh]

1. Since I want to ride at 30 to 35 km/h, it seems MXUS XF08C at 250W and 36V is not adequate for me. Is this correct?
2. It also seems that probably any motor at 500W and 48V (and labelled as 328 RPM?) is too much for me because I will not be riding it efficiently. That seems to narrow down selections to 36V 350W motors or 48V 350W motors or motor labelled 48V 500W 201 RPM. Does that make sense?
3. MXUS has a motor that is interesting, can be purchased cheaply as part of a kit, and seems to be in stock on Aliexpress. MXUS XF15C. Does anybody know anything about this motor, reliability, noise, can it run with sine wave controllers like S12S? It comes in 36V or 48V and 350W and 500W options. Which one?
4. Only available Q128C is on BMSbattery and it is motor only with options of 36V or 48V and 201 RPM or 328 RPM. Which one of these would be the best for my situation and how difficult/expensive is it to get a bike shop to build a wheel around it? None of the other Q motors are available for purchase as kits or just a wheel, anywhere so this would be the only option.
5. Finally, there are a bunch of Bafang CSTs with various options on Aliexpress, again 36V or 48V and 350W or 500W. Which one?
6. For all of the above, which controller? I am assuming there is no need to go with 20A or higher controllers but maybe max of 15A? Sine wave controller with LCD3 or LCD4? This would rule out S12S because of its high current, is that correct? What other controller then?
7. Same for battery, look for a 36V or 48V battery with maximum discharge current of 15A? Or only focus on 48V batteries?

It seems I can also buy MXUS kits directly from MXUS on alibaba.com and they seem to allow option of purchasing just 1. Did anybody order from them directly and with low quantity?

So what do you think? Can anyone help out with above questions? Thank you again for all the help so far and all of the information.

1. Not so.
If one was to go 48v and add a 20/22a controller you should comfortably reach 20mph+ if you have the stamina.

2. Ideal RPM will be about 260 at 48v, a 36v one run at 48v would need to be 201.

3. The hub will most likely be very good like the others, the 15c is a heavier build/stronger hub to take more amps and capable of 40km/h. Nearly all new hubs tend to be for sinewave a link to your find.

4. Topbikekit sell AKM 128C and other AKM hubs.
The BMSB 201 rpm hubs are incorrectly marked and listed as they go faster then 15/16mph, they can easily reach 20mph so they are more akin to 260rpm winding.

5. Go for 48v and select the winding you need typically 260rpm, 328 if you have no hills. The AKM 128 is as good as the Bafang CST but a lighter motor.

6. KT is tbh the best controller kit to go for, 20/22a is fine as you can regulate the current via the settings. The 22a & 25a ones I have are smaller then the S12s and are 9 fet sinewave, on Aliex you can choose Julet ones or older style connector ones.

7. 48v battery if you want 30 km/h, look for battery with min 20a discharge better still 25a.

 

[vfr400]

Power and voltage designations are not important characteristics. Motor speed is proportional to voltage. The same motor will spin 33% faster at48v compared with 36v.

Power is proportional to current and voltage, so a motor will give 33% more power at 20 amps compared with 15 amps, and 33% more power at 48v than eith 36v.

What burns a motor is inefficiency. Motors become increasingly less efficient when their speed drops below 50% of their maximum speed. The lost energy due to inefficiency is converted to heat instead of motion. Small motors burn faster because they can't absorb or shed as miuch heat as large ones.

The higher the current, the more heat you make, so it's better to run with higher voltage than current, though in some circumstances you use more current to get more speed for better efficiency, so less heat.

The bulk of ebike controllers and batteries are 24v, 36v and 48v. As said, regardless of what's written on motors, they don't care about voltage. It only effects their speed and efficiency.

It takes about 250w to hold 25km/h on an MTB type bike without pedalling and 1000w to hold 50 km/h. Assuming that you chose the motor well, efficiency would be around 70%, so you have to divide those powers by 0.7 to get the imput power you'd need. Only you know how hard you pedal.