Cadence rate against motor rpm ???

[(NoLongerRegistered#15675)]

Seems torque peaks around 1500 rpm on electric motors in yam ( and Bosch??) mid drive..after that it drops till motor reaches peak rpm..
Was wondering how this relates to cadence rate for two reasons.
A) Could be its more efficient in terms of mileage/ power use to use higher mode but higher gear with it.( ie keep motor at peak torque but going further per rev)

B) At what cadence rate will electric motor be over revved ? ( if there is such a term for electric motors, but you get idea)

 

[trex]

crank drives efficiency does not vary much with RPM. What happens is power = torque * angular velocity, the torque you can get drops when the RPM goes up.
the motor's power is limited by the controller, for a Bosch, that's 17A-20A or about 600W to 750W depending on programming.

 

[(NoLongerRegistered#15675)]

I realise that and crank efficiency/ motor efficency is different to overall efficiency.
For example if you had a diesel engine producing max torque at 1500 rpm , it would always give better mpg to change at say 1600 rpm. ( but lower performance)Motor efficiency ( ie power produced per unit used ,watts or cc of fuel) is different to overall vehicle efficiency..

Yes the motor may be producing more power higher up rev range per watt but bike is not travelling quite so far..t
Its similar to us when pedalling. ( our most efficient cadence rate is not necessarily same as bikes !!!)

By your argument bike would be equally efficient in any gear ! Leave it in lowest gear and see how it effects your range.
Question is at what point is it most efficient to change into higher gear, I suspect its at just past peak torque figure ( I think 1500 rpm)( and what is most efficient climbing cadence, again I suspect at motor,s peak torque rpm, which suggest using higher gear than you,d chose without power)
But that may not be riders most efficient ???
Hence question about cadence to motor rpm relationship. We need to know it to get best range.
At moment its like trying to drive a car efficiently for max mpg without knowing torque characteristics of motor or having a rev counter. The control unit is exactly that a control unit.

 

[trex]

By your argument bike would be equally efficient in any gear ! Leave it in lowest gear and see how it effects your range..

Yes, that's mostly correct. If you test your power consumption at gear 4,5,6,7,8,9, I doubt that you'll find much difference at the same speed. If you look at the plot of efficiency vs RPM (source http://www.ebikes.ca/tools/simulator.html ), the efficiency rises rapidly with RPM, reaching a maximum at around 80% of the no-load RPM. This is even more pronounced for inrunners, the type of motors used in crank drives. The gear reduction ratio of CD motors is around 25 against 4-5 in geared hub motors, CD motors get to be efficient 5 time earlier than geared hubs.

 

[Gubbins]

From a non technical point of view i have been experimenting with this idea for some time and my views are...
When the battery gets very low the high rpm power disappears first suggesting it needs more resources than are available to spin fast, whist at low rpm (cadence ) power is still available . In my unscientific tests I find I can go further up hill by pulling a high gear rather than spinning in a lower gear at the same speed. I use the power meter as I would a vacuum gauge on a car to ballance speed with power being used.
I tend to assume that if I am working hard then so is the motor.

 

[(NoLongerRegistered#15675)]

From a non technical point of view i have been experimenting with this idea for some time and my views are...
When the battery gets very low the high rpm power disappears first suggesting it needs more resources than are available to spin fast, whist at low rpm (cadence ) power is still available . In my unscientific tests I find I can go further up hill by pulling a high gear rather than spinning in a lower gear at the same speed. I use the power meter as I would a vacuum gauge on a car to ballance speed with power being used.
I tend to assume that if I am working hard then so is the motor.

Well I,d tend to agree, that,s exactly how I,d imagine it to be looking at torque curve of yam motor.
Trex's explanation is the theoretical efficiency as far as power transmission is concerned and makes no allowance for real situation ( ie bike won't do 20 mph in 2nd and won't climb hills in 9th)
Its the reasoning that gives cars mpg figures way higher than in reality.

I,ve found exactly as you did, ie more help available at lower rpm when low charge..which suggests to me using lower rpm ( higher gear) will extend range...

I,ve not had chance to experiment but will be doing so. ( ie changing up at low cadence for full charge against changing up higher) Would still be beneficial to know what cadence gives max motor torque)

So does anybody know the actual reduction ratio between chain ring and motor on mid drive systems ..???

And, what cadence ( if any) would start to damage motor....or what,s max recommended cadence rate on mid drive systems ? Nobody mentions it ..

 

[trex]

Would still be beneficial to know what cadence gives max motor torque

that's easy, maximum torque is at around 60% of maximum RPM, about 45-55 RPM.

I don't know the reduction on the Bosch system but expect it to be similar to Chinese CD motors, it's 15 on Bafang BBS01, 20 on the woosh Krieger.

 

[(NoLongerRegistered#15675)]

Cheers...Bosch system will be different to yam ( for chain ring but not cadence) I believe its chain ring rotates 2.5 x crank. Yam chain ring and crank are equal.
That's a low cadence...but presumably that means Cadence of around 50 matches 1500 motor rpm.
Roughly 30 to 1 reduction ??
So max motor rpm is not an issue..( if my estimate is correct) My max cadence is about 105 , still only about 3000 motor rpm.??!!

 

[trex]

I guess so too, but could not find a technical manual on the internet. Maybe a Bosch dealer can clarify this for us.

 

[Deleted member 4366]

I don't agree at all with much of what is written above. I think people are getting a bit mixed up.

All BLDC motors, whether crank-motors or hub-motors behave the same. They produce maximum torque at zero RPM and zero torque at maximum RPM.

Efficiency is different. It's zero at zero and maximum RPM, and it peaks at about 75% of maximum RPM.

Peak power comes at about 65% of maximum RPM.

Overall efficiency of battery use from the rider and motor has little relationship to motor efficiency. The situation is completely turned on its head because you can adjust the motor's power or torque from the control panel. Maximum battery efficiency will come when you set the assistance to zero. Everything else depends on how hard you pedal and what your cadence is. Trying to keep the motor at its most efficient speed will not give you good efficiency. The only thing that gives you good efficiency is to pedal harder.

If you want to climb hills with the minimal effort, turn the power up to the maximum and pedal slowly. If you want to go up hills as fast as possible, turn the power up to maximum and pedal at the speed that you can make your maximum power. If you want to go up a hill with the least amount of battery, select zero assistance and the lowest gear, then pedal as hard as you can.

 

[Gubbins]

I don't agree at all with much of what is written above. I think people are getting a bit mixed up.

All BLDC motors, whether crank-motors or hub-motors behave the same. They produce maximum torque at zero RPM and zero torque at maximum RPM.

Efficiency is different. It's zero at zero and maximum RPM, and it peaks at about 75% of maximum RPM.

Peak power comes at about 65% of maximum RPM.

Overall efficiency of battery use from the rider and motor has little relationship to motor efficiency. The situation is completely turned on its head because you can adjust the motor's power or torque from the control panel. Maximum battery efficiency will come when you set the assistance to zero. Everything else depends on how hard you pedal and what your cadence is. Trying to keep the motor at its most efficient speed will not give you good efficiency. The only thing that gives you good efficiency is to pedal harder.

If you want to climb hills with the minimal effort, turn the power up to the maximum and pedal slowly. If you want to go up hills as fast as possible, turn the power up to maximum and pedal at the speed that you can make your maximum power. If you want to go up a hill with the least amount of battery, select zero assistance and the lowest gear, then pedal as hard as you can.

Whenever I read posts from people like you I find myself impressed by both your knowledge and the way you put things across to make it understandable. (Definitely not being sarcastic here)

Having said that wherever I go it is uphill and as I always set off with a full battery I have gained some experience in my battery behaviour... and in turbo no matter how hard I pedal the battery goes down quickly on hills and if I really spin in a lower gear it goes down considerably faster.

Thinking about it properly my longest runs (including some big climbs) have been in tour with a moderate cadence and not spinning fast, only using sport/turbo when absolutely necessary.

My bike is over geared with a 44t chain ring and when it comes back it will have a much smaller front ring which will make a difference, I just don't know what yet.

 

[trex]

d8veh is correct, my mistake.
Maximum torque is at zero RPM and peak power is at 65% of maximum rpm, around 45-55 rpm. You go uphill fastest if you keep your cadence to 45-55 rpm, you have maximum assistance but that does not equal to having maximum torque. You have maximum torque when you stall.

 

[(NoLongerRegistered#15675)]

Think

I don't agree at all with much of what is written above. I think people are getting a bit mixed up.

All BLDC motors, whether crank-motors or hub-motors behave the same. They produce maximum torque at zero RPM and zero torque at maximum RPM.

Efficiency is different. It's zero at zero and maximum RPM, and it peaks at about 75% of maximum RPM.

Peak power comes at about 65% of maximum RPM.

Overall efficiency of battery use from the rider and motor has little relationship to motor efficiency. The situation is completely turned on its head because you can adjust the motor's power or torque from the control panel. Maximum battery efficiency will come when you set the assistance to zero. Everything else depends on how hard you pedal and what your cadence is. Trying to keep the motor at its most efficient speed will not give you good efficiency. The only thing that gives you good efficiency is to pedal harder.

If you want to climb hills with the minimal effort, turn the power up to the maximum and pedal slowly. If you want to go up hills as fast as possible, turn the power up to maximum and pedal at the speed that you can make your maximum power. If you want to go up a hill with the least amount of battery, select zero assistance and the lowest gear, then pedal as hard as you can.

Think you are over simplyfying real world situation.
You are perfectly correct the motors mentioned do give max torque at zero rpm but at approaching zero rpm are woefully ( for e motors) inefficient. ( sub 60 %)
Efficiency varies between around 72 % at 1500 rpm up to max of 97% at between roughly 2200 to 2800, and then falls back to 80% or so at max rpm ( profile graph I found gave maxx rpm 4800)
Therfore it stands to reason to keep motor at as near 2500 for max efficiency.
Arguments around electric motors not requiring gears fail to recognise fact that in our application motor is way underpowered for job in hand. And the fact that mtb cover a massive range in applications..from 35 mph down some path to slow technical ascent of single track. Imagine been in wrong gear for either and effect it would have on efficiency, yours and motors. Cant think of another vehicle requiring such a range of gearing ??
We have limited torque,power available and power stored. In this scenario gear box can have a massive effect on efficiency. ( only my thoughts)


You often hear people say e motors do not need gearboxes, strictly speaking that is completely wrong. They generally do not need multiple speed reductions, which is different. Few operate direct and those that do tend to be inefficient. Once application requires a multi speed gearbox, it stands to reason the use of that gearbox must affect overall efficiency.
I,m trying to establish the style of riding a mtb mid drive pedelec ( in this case Yamaha) to give maximum aid for minimum current draw? Perhaps there isn't one ?

And BTW merely pedaling harder has nothing to do with efficiency,just go back to none electric with zero current draw, and of course the 100 year argument about most efficient cadence rate. ???

 

[flecc]

So does anybody know the actual reduction ratio between chain ring and motor on mid drive systems ..???

Initially on the series 2 Panasonic crank units the total reduction ratio was 13.4. Later a change of standard chainwheel made it 13.8. On these units the motor to chainwheel reduction is in two stages due to having a separate motor drive sprocket onto the chain.

what,s max recommended cadence rate on mid drive systems ? Nobody mentions it ..

On the earlier Panasonic units the maximum motor power was limited to a cadence of 40, equal to 9.4 mph in top gear, power declining progressively above that cadence and speed in top gear to zero at 15mph.

That continued on the series 2 units until 2010 when the cadence restriction of full power was removed on export models.
.

 

[trex]

I,m trying to establish the style of riding a mtb mid drive pedelec ( in this case Yamaha) to give maximum aid for minimum current draw? Perhaps there isn't one ?

And BTW merely pedaling harder has nothing to do with efficiency,just go back to none electric with zero current draw, and of course the 100 year argument about most efficient cadence rate. ???

yes, there is. Maximum efficiency is around 80% of maximum rpm.
You select the right gear where you feel most comfortable pedaling then stick to 60-70 rpm.

 

[Gubbins]

High cadence can take a lot out of the rider as well.
I feel at my best around 72. Dropping to 60 on hills.
It would seem the a recreational cyclist (me) can use 60% of their energy just moving their legs..
http://www.cyclingweekly.co.uk/news/latest-news/why-amateurs-shouldnt-try-to-pedal-like-chris-froome-191779

 

[(NoLongerRegistered#15675)]

Yep whenever I read about cadence I think I,m way too slow. But then again ( I,m not comparing my self with any one on tour) tour winners have a massive range. ( Think Lance A was one of highest, believe it averaged 100 . ( only by memory, not checked)
Does seem pedelecs are geared more towards numpties like me rather than tour competitors..
Beginning to think with the 15.5 mph powered limit that mtb are more suited to e power than road bikes. My rides often average 10 mph, and cadence around 65....Cant imagine any road riders with those figures..

That article is great, sort of contradicts what many have been telling us for years. I do know if I,m feeling tired I,ve always found pulling higher gear is beneficial to finish ride but used to be argued higher cadence puts emphasis on cardiovascular system and low cadence in muscles themselves. ( never found that but always assumed its to do with my size/ weight and rugby players legs.....

 

[Gubbins]

Yep whenever I read about cadence I think I,m way too slow. But then again ( I,m not comparing my self with any one on tour) tour winners have a massive range. ( Think Lance A was one of highest, believe it averaged 100 . ( only by memory, not checked)
Does seem pedelecs are geared more towards numpties like me rather than tour competitors..
Beginning to think with the 15.5 mph powered limit that mtb are more suited to e power than road bikes. My rides often average 10 mph, and cadence around 65....Cant imagine any road riders with those figures..

That article is great, sort of contradicts what many have been telling us for years. I do know if I,m feeling tired I,ve always found pulling higher gear is beneficial to finish ride but used to be argued higher cadence puts emphasis on cardiovascular system and low cadence in muscles themselves. ( never found that but always assumed its to do with my size/ weight and rugby players legs.....

You could try giving the rugby player his legs back and using your own![emoji56]

 

[flecc]

Think Lance A was one of highest, believe it averaged 100 . ( only by memory

Lance Armstrong routinely rode with a 110 cadence. His great rival, Jan Ullrich, was often quoted as having a very slow cadence, some saying as low as 75, but that just wasn't true. When he was clocked it turned our his cadence was near to 90, but that just looked slow when riding with Lance.

Since both had drug use bans, it seems that usage doesn't influence cadence.

The main reason for avoiding low cadences like 40 is the damage they do to knee joints. The higher the cadence for a given distance and energy input, the less pressure per stroke. The sum of a number of low pressures does not equate to a lower number of high pressures in this respect, hence knee damage being a common affliction of long term cyclists.

Cadences of 60 to 70 are a sensible range for average cyclists, and they should always avoid the temptation to drop to low slogging cadences on hills if they wish to avoid joint replacements in later years.
.

 

[(NoLongerRegistered#15675)]

You could try giving the rugby player his legs back and using your own![emoji56]

He wouldn't want them now, almost cream crackered....especially zee knees....