BBS02 Chainring 52T cheapest one ?

[alexis57]

Hi,

For now, I can go as fast as 45km/h with my Chinese mountain bike with the stock bafang chainring.
Then I use a lot the battery when I'm at this speed.
I would like to change it for a 52T in order to reduce the speed and then consume less and go faster.

The cheapest I found is EM3ev here : http://em3ev.com/store/index.php?route=product/product&product_id=193
27€ shipping incl.

Do you know another shop ? I didn't find on ebay..

Thank you !

 

[KINNINVIEKID]

Thats the only option really but get a spare throttle etc while ordering as the shipping is the same price up to 2.5Kg anyway.

 

[alfantastic]

Hi,

For now, I can go as fast as 45km/h with my Chinese mountain bike with the stock bafang chainring.
Then I use a lot the battery when I'm at this speed.
I would like to change it for a 52T in order to reduce the speed and then consume less and go faster.

The cheapest I found is EM3ev here : http://em3ev.com/store/index.php?route=product/product&product_id=193
27€ shipping incl.

Do you know another shop ? I didn't find on ebay..

Thank you !

I may be missing the point here, but surely reducing the chainring size will use less battery power!

Increasing its size will create more load on the controller in any selected gear, and hence draw more amps.

Also, be careful that the 52T doesn't make contact with your chainstay.

 

[leo99]

As alfantastic just said if you take a bigger chain ring if pedal at the same cadence you will go faster and have a higher multiplication . If you want more efficiency you should aim for a custom 42 tooth or normal 44 tooth chainring. It will reduce your top speed but give you better torque on lower gear

 

[alexis57]

Mmmmh it's opposite way.. since the energy efficiency decreases with motor speed, for the same speed, I will use less battery power... (for same load between both chainrings then for the same output speed)

If I decrease the chainring, I'll get more torque (still at the same output speed) since the motor will run faster. The only thing this is useful is for climbing hill, because the electric motor use current then will be more hot.

But you/I didn't mention about the bike's gear. What I said is with the same bike's gear !
I already can choose my "torque" or "power efficiency" with the bike's gear. And it's not at all when the motor is at max speed.
Then at max power speed let's say 45km/h, I use more battery than if I was at the half of max power speed with a bigger chainring. (still constant load = constant bike's speed)

I maybe made a mistake in my reasoning but I think it's mostly correct. I didn't find a good efficiency graph but the shape should be same like other electric motors. (max efficiency is never at max speed)

 

[alfantastic]

I already can choose my "torque" or "power efficiency" with the bike's gear. And it's not at all when the motor is at max speed.
Then at max power speed let's say 45km/h, I use more battery than if I was at the half of max power speed with a bigger chainring. (still constant load = constant bike's speed)

But surely if you wanted to travel at 45km/h with the 52T, the motor would have to draw more amps from the controller, so that the motor will have enough torque to maintain that speed with the higher gearing?

The 52T may be rotating slower to keep the same speed, but the motor will need to push harder to achieve this.

I'll be honest, I don't think you'll notice a great deal of difference in battery consumption, whether more or less, by changing to the 52T.

Anyone else shed some light on this, my brain hurts :wink:

 

[tahustvedt]

If you're limited by the gear ratio, and you motor is spinning at a high rpm, then you will be able to go faster with a larger chainring, and will also use more power. Efficiency will be roughly the same unless the motor is overloaded. You will not save energy by going faster. Energy spent per unit of distance will go up because of increased air resistance and rolling resistance.

 

[alexis57]

But surely if you wanted to travel at 45km/h with the 52T, the motor would have to draw more amps from the controller, so that the motor will have enough torque to maintain that speed with the higher gearing?

The 52T may be rotating slower to keep the same speed, but the motor will need to push harder to achieve this.

I'll be honest, I don't think you'll notice a great deal of difference in battery consumption, whether more or less, by changing to the 52T.

Anyone else shed some light on this, my brain hurts :wink:

Mmmmh thank you for reply me but are you sure you studied electricity/electronic/physic ?
At 45km/h with 52T or 44T, the load is same... omg the load doesn't depends on the chainring..... the load depends on air, level of the road and weight on the bike, means speed and your weight.
Load = power, then power = constant = same consumption. Even without see what happens in the motor/controller, it's mathematic. You have the same
Same thing with your car. For a constant speed, you'll consume less fuel with a lower gear than a higher. Ok, after that it depends on the speed of the motor but basically this is true.

Why the motor will need to push harder to achieve this ? it's totally false, with a constant speed and the road at the same level. Or explain me where the power should go ?
Small explanation, for climbing a hill, it's not good because the motor will turn really slowly and then the efficiency will be really really bad (watch a curve of motor's power) and then the motor/controller will heat a lot (since many heat losses => increasing current for the same "voltage", basically).

Of course everything this is ok only if I use longer the bike at 45km/h (with 5th gear and max motor speed) since I can use the gears to manage the speed motor.

The light is made, I explained you in details...

Anyway if I change this it's not to improve the battery consumption, I mentioned it only for a second advantage.

 

[alfantastic]

Yeah, my apologies. I totally misread your quote:

"I would like to change it for a 52T in order to reduce the speed and then consume less and go faster"

When you said "consume less", I thought you meant pies. Now I'm understanding you meant battery power.

Simple Jack over and out

http://www.imdb.com/title/tt0335266/

 

[alexis57]

Yes, I didn't read myself but I could have written more understandable xD It wasn't clear at all.

Haha good movie ! Even if you can see only barely Tokyo.

 

[Samd]

Actually on the flat you'll need about the same amount of kinetic energy to achieve a given speed, all other things unchanged (tyres, pressure). The efficiency band of the motor is pretty similar across that rev range.

I sell an adapter via ebay and here, you can put any local chainring on it if you like...

 

[alexis57]

Actually on the flat you'll need about the same amount of kinetic energy to achieve a given speed, all other things unchanged (tyres, pressure). The efficiency band of the motor is pretty similar across that rev range.

I sell an adapter via ebay and here, you can put any local chainring on it if you like...

Please give me the graph of the motor's power. I didn't find it. BBS02 48V 750W. Or you just guess that it's pretty similar ?

 

[pchen92]

Same thing with your car. For a constant speed, you'll consume less fuel with a lower gear than a higher. Ok, after that it depends on the speed of the motor but basically this is true.

You are comparing ICE engine with electric motors, it's completely different :lol:

Why the motor will need to push harder to achieve this ? it's totally false, with a constant speed and the road at the same level. Or explain me where the power should go ?

Power = torque * speed
If you have a bigger chainring, the speed of the chain (or of the chainring) will be slower to achieve the same speed. So as we are talking about same speed, it means also same power and then, as the speed of the chain is slower, the torque increases to compensate. That's why alfantastic said the motor will push harder (ie torque).


Don't believe that if you want a better efficiency at constant speed, you will have to reduce the motor speed (by having a lower reduction and using lower throttle). This is absolutely false.

 

[alexis57]

You are comparing ICE engine with electric motors, it's completely different :lol:

Of course it's different but it's still true.

Power = torque * speed
If you have a bigger chainring, the speed of the chain (or of the chainring) will be slower to achieve the same speed. So as we are talking about same speed, it means also same power and then, as the speed of the chain is slower, the torque increases to compensate. That's why alfantastic said the motor will push harder (ie torque).


Don't believe that if you want a better efficiency at constant speed, you will have to reduce the motor speed (by having a lower reduction and using lower throttle). This is absolutely false.

It was a rhetoric question... :/ everybody learned this equation at high school :/ but we don't care at all the motor will push harder (ie torque), I just see the consumed power.

I'm waiting for your explanation about the "absolutely false".

What you are saying like a "rule" is not convincing at all since you don't explain it. Value => 0
I explained clearly (I think) why it's supposed to be true.
I've never said the gain will be very high, just decreasing the motor's speed (from max speed) for a constant bike's speed, increases the efficiency.
Just look at any brushless power/efficiency graph. (since nobody gave me the bbs02's graph)

Please think by yourself, not just repeat what you read on this or another forum. "increase chainring is bad" "decreasing the motor's speed is bad". Just use mathematics.

 

[pchen92]

Deja, evite de prendre un ton condescendant, tu n'as pas la science infuse.
Deuxiemement, les questions de rhetoriques sont mal venues, on est sur un forum international et par ecrit donc le ton de la voix ne peut pas passer par message.

You are comparing ICE engine with electric motors, it's completely different :lol:

Of course it's different but it's still true.

No, just do some research on electric motor efficiency curve vs ice curve. A ice efficiency peaks between 1300 and 2500rpm whereas an electric motor peaks almost at full rpm. Peaks power is at full rpm for ice and ~ half rpm for an electric motor. Compare apples with apples.
That said, let's get back on topic :

Power = torque * speed
If you have a bigger chainring, the speed of the chain (or of the chainring) will be slower to achieve the same speed. So as we are talking about same speed, it means also same power and then, as the speed of the chain is slower, the torque increases to compensate. That's why alfantastic said the motor will push harder (ie torque).


Don't believe that if you want a better efficiency at constant speed, you will have to reduce the motor speed (by having a lower reduction and using lower throttle). This is absolutely false.

What you are saying like a "rule" is not convincing at all since you don't explain it. Value => 0
I explained clearly (I think) why it's supposed to be true.
I've never said the gain will be very high, just decreasing the motor's speed (from max speed) for a constant bike's speed, increases the efficiency.
Just look at any brushless power/efficiency graph. (since nobody gave me the bbs02's graph)

Please think by yourself, not just repeat what you read on this or another forum. "increase chainring is bad" "decreasing the motor's speed is bad". Just use mathematics.

If you don't know this website http://www.ebikes.ca/tools/simulator.html , I would advise you to play a bit with it, it should help you.
We don't care about mathematics because we are talking about real values, real consumption. Again compare apples with apples. We want facts, not theoretical formula. I won't send you my colleagues thesis on electric motors

 

[Samd]

Actually it *is facts and math*. Thats why I have a B.Eng degree. But you're still kind of there.

You just need to overlay the torque vs power equation over the top of a motor's efficiency vs rpm chart.

The reality is that the standard chainring pushes most people off the peak of the efficiency vs rpm curve for BBS units. That's why I sell so many chainring adapters.
If you like on the flat you can get away with the stock one and not notice too badly.

 

[alexis57]

Show me an efficiency curve with peak at max speed :O

Even if it doesn't decrease like an ICE motor, it still decreases.

If you don't know this website http://www.ebikes.ca/tools/simulator.html , I would advise you to play a bit with it, it should help you.
We don't care about mathematics because we are talking about real values, real consumption. Again compare apples with apples. We want facts, not theoretical formula. I won't send you my colleagues thesis on electric motors

Are you serious ?!
You don't care about mathematics but the website you just sent me is FULL ONLY MATHEMATICS since it's a SIMULATOR.
You are talking about real values but I've never seen an experiment curve here, and even less from the BBS02.
Obviously, you should learn from your colleagues ...

Again, you don't know how to read a curve...
I didn't want to talk about it but I need to teach you how to show what you are saying.

Let's take a Ninecontinent 3007.

The speed is in km/h since it's a hub motor (no gear) but let's say it's like rpm. I let you make the conversion.
(I'm too kind : you know, junior high school equation : P=2*Pi*R)

I see the maximum efficiency is at 57km/h and the efficiency at 0% is at 67km/h, 10KM/H difference / 15% it's fu**ing big. Max eff at 85%. (max efficiency at full speed you said ?!)

I want to decrease the power consumption at max speed, means I'm at 0% efficiency (haha, real values you said ?!) when I'm at full speed.
Thanks to the gear/chainring, I can decrease the motor's speed and stay at the same bike's speed.
If a decrease the speed of about 10km/h (15% less than the max rpm), I'll get max efficiency.
52T instead of 44T : 18% less, I decreased the power consumption 8)

I just showed that you don't know AT ALL what you are talking about.

Je ne m'abaisserai pas à montrer celui qui a la plus grosse à coup de "thèses de mes collègues" :/ je ne dirai pas mon job et tout le monde s'en fiche mais apparemment j'en connais un peu plus que toi sur les moteurs et comment analyser les données que l'on me donne.
Tu n'es pas obligé de répondre

Bye !

My main problem is I have a bad Chinese mountain bike, then the top speed is 40-45km/h at full motor's speed (full throttle). That's why I thought to change the chainring instead of the gears.

If someone has the BBS02 experiment curve, please send here !

 

[Samd]

If you got two masters in science it means nothing to me as B/Eng Mech.
This shit is straight out of an undergrad Mech Eng course. Its basic math across two sub-disciplines.

 

[pchen92]

@Alexis:

It's again false.

1) the simulator is made with real number (test-bench) and then it's extrapolate but really close to the reality for "small power".

2)

whereas an electric motor peaks almost at full rpm

Can you read ?

3) You forgot the load of the bike at speed. Therefore, you're not running it at full rpm as you think , but close (see on the simulator), right where the efficiency curve peaks.

The 2 setups you want to compare may have the same efficiency at a constant speed, on the flat and with virtually no wind.
But the reality is, the road won't be perfectly flat, there is wind, ... And thus, a bigger reduction will run better (more efficient) through hills and headwind because it will be closer to the peak efficiency. To see this, you just have to run a motor in the simulator with 2 different wheels size and a fixed grade

You probably won't notice a change in consumption because of exterior factors (except if you want to climb a mountain).

 

[alexis57]

I think I'll stop here, I don't want to copy paste what I said.

2) "almost at full rpm", 97% is almost, 85% is far.
Now the motor's efficiency depends on the load :|

"Copy paste" from my last topic.

3) No one knows when the controller stop the motor, for me it's maximum speed.
A bigger reduction will run better for a high load because the motor is not powerful enough to keep the speed (you are at the left of the max efficiency) and then with higher reduction, you will make turn the motor faster then you will translate to the right (to the max efficiency).
In my case, I'm at full speed ( right ), with a lower reduction (44T->52T) will translate me to the left (max efficiency).

It doesn't mean anything to say "if you run a motor with 2 different wheel size"... Depends on the speed you will run them.
On my case, one full speed, the second one 15% less, the one at 15% less will consume less.
It's theoric, of course I know in reality I won't get anything but I won't lose anything too. (for the one who told me the motor will push harder)

BUT if you are able to tell me why (and not "I read somewhere" "someone told me") my bbs02 don't go at its max speed when I'm at 40-45km/h at full throttle on flat road, then yes, I'll be ok to say I won't gain any power.

 

[pchen92]

3) No one knows when the controller stop the motor, for me it's maximum speed.

No, maximum speed (full rpm) is only reach when you have no load. It never happens except in a very particular case: when you have enough speed in downhill to balance the full rpm of the motor with your speed. Above that speed, the motor is regenerating energy (or freewheeling in your case). Under that speed, the motor is producing power and therefore submitted to a load.

For the rest, this graph shows it all


Wheel size act as gearing (ie 24" =44T and 26" =52T). You can see that the system A is a bit more efficient than the system B.

To illustrate what I said above: when the load is bigger, the difference in efficiency increases. I put a 5% grad and the setups are more powerful

 

[alexis57]

Then you said the motor in load even small cannot go faster than 85% of his max speed ? First time I hear this... Please proof.

When I tried, I see this :

Which confirms what I said.


Where do you see the efficiency is a bit different ? I don't see any difference. In "chart options", you can set "RPM" for "X Axis units" and you'll see it's exactly the same curve. And fortunately !!, the efficiency/power curve doesn't depends on the wheel size :|

For the difference of the efficiency at a different load, it's silly,I don't care at all, I won't do 44T 0% and 52T 5% :/ since the beginning I'm talking about difference at same load, but at 5%, you still can see the same difference than the graph I sent above. (which confirms what I said again)

As you said, it's an extrapolation of experiment data then it's not reality (and by the way, extrapolation is less efficient than interpolation, everyone who worked on system modeling could tell you). Moreover, this website considers controller etc...
I don't know how they use the "grade" (gravity's force?! or ...) then I won't talk about their results.

Anyway, for now, everything shows that changing 44T to 52T will be more efficient when I'm at top speed.

Next.

 

[pchen92]

Obviously, you don't know the difference between power needed and efficiency. You must be novice.

The red curve on the simulator represents the power of the setup (output power, power at the wheel).
The black curve is the load depending upon speed.
Hence, the speed of the setup will be at the intersection of the two curves.

Please, look at the section "How to use the simulator" beneath the simulator next time.

Here you go:



Now stop trolling and saying you're right because you're simply not

End of story. That's my last post in this thread. You can contact me if you want further explanation.

Enjoy the EV grin 8)

 

[nioko]

Alexis, what I'm about to write is a fact, and I won't argue about it:

My BBS is Limited to 25A, if I run up hill in my top gear, it is slower, than if I select a lower (the proper) gear. For me this says it all, Power stays the same, but speed increases: It must be more efficient in the lower gear.

 

[alexis57]

I think also we'll stop here, we are talking totally different situations.
AND it wasnt my question at all. (I wonder who are trolling)