What makes an efficient on road e-bike?

[flecc]

Yes, no difference Stuart, because if you can pedal the hub faster than the motor is driving, it will be spinning uselessly at maximum revs the other side of the freewheel and doing nothing. That's what happens if the throttle is kept wide open when pedalling fast downhill.

Surprisingly though, there's almost no power wasted. I once wanted to flatten a half charged battery to do a test, so with it in the Torq, I turned it upside down and taped the throttle wide open with the wheel spinning at an indicated 26. something mph.

Eight hours later the battery was nowhere near flat, the wheel still spinning just as fast, and that from half charge. So shutting off the throttle downhill probably isn't worth bothering with for all the power it might waste.
.

 

[coops]

Ok, thanks for clearing up that one flecc.

I really should give up the chips too I guess....

To John: What do you think of the pannier battery idea for longish range trips then? Is this more in line with your original ideas? I'm suggesting it out of slight desperation of finding a suitable ebike candidate for "modifying" more than anything, but I think if a good motor & controller can be found (skip the Crystalyte 400's I think - I didn't know they were so heavy ~8kg each it seems!) its another option .

Stuart.

 

[coops]

It's already on the market Stuart, and at under £1400 it's cheaper than you could build yourself.

It's the eZee Forte (or Forza)

The Velovision test in very hilly Sheffield returned 15 miles range, same as the Torq in hilly territory, and from the same 36 volt battery. But it speeds to 20 plus derestricted like the Torq and it had no trouble zooming up a 1 in 5 (20%) in Sheffield, pedalled by a vicar, so exactly what you are asking for, a Torq that climbs hills easily.

Problem solved!

The eZee approach with the F series is a US style motor restricted down to UK levels of course.

Well, I've been all round the houses I know but I'm beginning to think so, on all cost, component & performance grounds. I'd probably go for the forza of the two, uncertain about the ezee assistance factor & carrying spare battery, but I'll ask about that elsewhere .

Stuart.

 

[flecc]

Of the two, the Forza would be my choice too Stuart. It'd certainly have no trouble climbing hills fast with a spare battery or two on board. I'm not keen on twiddling onboard power control switches, those being on the BionX and Sparta too of course.

A simple throttle and a human attached is all that's needed I think.
.

 

[coops]

Yes, as far as I can tell the ezee assistance factor works just like a "sticky" modified throttle in pedelec mode (it allows finer tuning of power level which is set by a dial; still continuously variable like the throttle), so I'd also just go for a simple throttle which I could modify to "stick" if required.

How to best carry a single spare battery is a question though, especially if I stick with the slightly heavier NiMH? Two spares would be more balanced I guess, but a lot of extra weight & unnecessary for many trips.

Do you have any suggestions flecc? A rear-rack battery carrier add-on? .

 

[flecc]

I've always preferred lower in a pannier Stuart, and I regularly ride like that with one only. There's no balance problem even with a 5.5 kilo NiMh in a high pannier on a Torq and in traffic too.

The kinetic energy of the bike and wheel gyroscopic action tend to keep a bike stable regardless once rolling, you're just riding minutely tilted to one side, but it's far too small a tilt to see.
.

 

[coops]

Thanks flecc

Do you need especially strong panniers for that, and inflexible ones to prevent the batteries moving around on corners etc.?

If I'm pushing the boat out that far, I may as well get 2 spares to use till I lose weight, then one may suffice after that, if the capacities haven't dropped . 3 lots of 36V 9Ah... thats virtually 1kWh! I like that! 3 times the range too, so at moderate speed (17-18mph) and pedalling I'd say around 70 miles .

Stuart.

 

[flecc]

And why not. I use ordinary soft Altura panniers, about 15 litre size, and sit the battery on the slant, base forward and leaning back, the pannier top enveloping the top of the battery and holding it at the rear of the pannier, so it's stable.

The first time I carried a battery on the carrier it was a Giant Twist one and this happened, scroll down slightly: busted

so it's not a favourite method, though I have carried eZee ones in the box that way on the odd occasion.
.

 

[coops]

Yes, the rear carrier seems too high for the weight, not very secure either & too much risk of damage if it falls off as you say...

Looks like panniers are enough then (when I said rear-rack battery carrier "add-on", I did mean a pannier style one, like a sort of "double Grandad" job, not on top of the carrier ). I'm sure you've posted that info on carrying batteries before, now you've said it, so apologies if thats so, but it was a long time ago, before my ebiking days and thoughts of extra batteries for long range trips .

Stuart.

 

[kraeuterbutter]

interesting discussion..

for "road e-bike" and efficient..

for me, this looks very efficient (roll restistance, aerodynamic drag, light weight, motor uses the bikes gearing, ...)

battery: 24Volt and 6,5Ah
with lipos maybe you can increase that to 36Volt at same capacity..
frame would have to be made for new..

the weights of ~16kg is for sure cool...

and for your batteries (light weight, high distance)
when you are building your packs by your own, you can get for a
37Volt 12Ah pack (including shrinkrap, including balancing/equalicing-connectors)
for around 2.4kg

or if you want to be lighter:
for about 1.6kg 37Volt and 8Ah

and the 10kg pack you mentioned:
(if money is not of big concern) i can build you a
37Volt pack with ~50Ah

of course high-powercells... (with low-power/high energie-density cells for same weight even higher Ah would be possible)

 

[flecc]

Yes that is quite efficient kraeuterbutter. I have a bike with that same Panasonic power unit and battery, the Giant Twist Lite.

I'm not entirely convinced about using the cycle gears though, especially in the UK. The power band of Hall effect motors is wide, and our effective range of e-bike usage is from 5 mph to a maximum allowed of 15 mph. In fact the Panasonic unit is arranged in the UK to phase down power from 13 mph to comply with European law, so the full usage band covers 8 mph only. That does not need lots of gears of course, and when you consider that gears lose some efficiency, it's questionable whether there's much advantage.

After all, we don't change gear on our way to 15 mph in our cars!
.

 

[kraeuterbutter]

well.. comparing to a car i think would not work on this..

you also don´t have to change gears from 0-25mph on a car..
nevertheless bikes do profit from changing gears on a steep hill when motorpower is limited...
three ways:
1.) change gearing, so motor can spin still efficient also when going slowly up a hill
2.) live with very bad efficience
3.) use a much overpowered motor, so that speed will not go down that much when going up a steep hill

however: when iam driving a bike like this "Yellow Dream" from Prima, i do not want to stay at only 15mph anyway
for driving with only 15mph there are much more comfortable bikes out there

is this bike still produced ? (the prima)
for sure it will be very expensive..

 

[flecc]

In practice our hub motor bikes mainly have peak torque at about 8 mph, so I don't think gears would really gain so much efficiency, there's no real gain above that speed, and at most we'd only need one more gear below that for steep hills. Ideally that's one gear for peak torque at 6 mph and another for peak torque at 10 mph, with the power phasing down from 13 mph to comply with the law. That's all that's needed at most, but there are no two speed efficient gear units.

My hub motored Q bike has higher efficiency than the Panasonic geared unit bike, and some new commercial hub motors are also beginning to exceed it's efficiency in our restricted legal use. With hub motors now able to do anything that today's geared designs can do, there seems no point in bothering with the complications.

I disagree that cars cannot be compared over such a restricted band as 8 mph, it's too narrow for the engine type to make any difference. Even a twisted rubber band might cover that!
.

 

[JohnInStockie]

Giant Twist Motor vs Hubs

Thinking of the Twist motor and any other 'drive through gears' type motor (if there is any), I dont relly understand the way that these motors work in comparison to Hub motors.

As I understand it, with hubs, you need to specify the range or power band you want and set the bike up acordingly.

With the Twist motor, the power is driven through the gears. Does this mean that the motor is always in its most efficient power band, and its just your choice of gear that changes it?

If thats the case, then in theory wouldnt a Twist style motor also be the most efficient and effective motor for an e-bike what ever the speed (if there were no restrictor and the gear range was ample)?

John

 

[flecc]

Well, yes and no John!

If there was no speed restriction at all and a wide range of speeds as in a car had to be catered for, a range of gear options would be needed, but since there are speed restrictions, as I said above, just two gears is more than adequate to cover 5 mph up to 13 mph at which point power starts to phase down.

There's a limit to using gears. If you tried to use all 8 in an 8 gear system to cover that 8 mph band between 5 and 13 mph, you'd always be changing gear and never driving the bike!

Second, although there's a peak point on the power curve, these motors slope off gently either side, so the power band is usable over a range of speeds, not just that at the peak. Since a cycle hub gear loses about 15 to 16% efficiency, the power curve fall off at a changed road speed has to be over that percentage for a gear change to be worth doing.

That's why I said two gears is enough on a legal motor, one putting peak torque at 6 mph so the power band at that point covered steep hill requirements, and another gear with peak at 10 mph to cover the upper legal speeds.

The hub motor approach is to provide more power, and with the peak usually at a midway compromise of about 8 mph. Then the power is sufficient at all points on the power/torque curves to cover the legal speeds and cope with hills. Although that might seem to be very inefficient due to the more power provided, in practice it's not for the following reasons.

First there's minimal mechanical losses with the simple hub motor driving the wheel directly and no gear losses either.

Second, the considerable performance gain from the extra power over the efficient parts of it's band gives it the edge in that respect.

To date that's still left hub motors a touch less efficient usually, but it's changing now. I've beaten the Twist efficiency with the Q bike now, and it looks like the Nano Brompton has too from it's test report, both private efforts of course, but others are hard on the heels.

I think this is why the pendulum has swung now. With design advance, the reducing gain from geared drive makes it less attractive than the low cost and reliable simplicity of the hub motor.

If we get a high speed 20/25 mph class for e-bikes, gear drive really would be better then to cover that range.

It's even questionable whether that 6 mph low gear I suggested is worth it, since the slower the speed, the less power is need for the climb, again a physical factor on the hub motor side.
.

 

[kraeuterbutter]

hmm.. i see

question:
inwheel-hub-motor

it goes 25mph at flat and full throttle

now there is a hill, a very steep hill

i still have full throttle
but of course 25mph are not possible anymore..
let say the hill is REALY steep, so the bike slows down to 10mph at full throttle..

that must be some horrible efficience than..

at least at this situations, a geared motor must be much better in efficience..
do you agree ?

i have just this diagramm for supporting/nourish my thoughts:
http://www.kraeuterbutter.at/Bilder2/sonstiges/Messwerte Mabuchi Lehner/Mabuchi RS-540SH-5045_Bild3.jpeg

lets assume the 15.000rpm of the motor are ~25mph (running flat)
efficience near 70% (~6A current)
outputpower: ~50Watt

the same motor given so much load, that rpm drops to 6000rpm (would be ~10mph) --> efficience goes down to 25% !!!
(current rises to ~25A)
outputpower: ~95Watt

you see what i mean ?
now the same motor - geared 1:2 for easy calculation..
we still want to reach the hills top with 10mph
but the motor is now allowed to spin with 12000rpm to reach that..
for that the diagramm says:
efficience ~60-65%
current ~12A
outputpower: ~90Watt

conclusio:
1.) the motor is of course to small for a bike, but the physics will not be that different.. (lets assume, its for a children-bike with 35kg light driver )

2.) power at most efficience is 50Watt, running on flat surface

3.) on the hill: without gear you get 95Watt Power from the motor..
efficience down at 25%, ~25A current needed !!

4.) the same motor, the same hill, the same speed to run up the hill
--> but 1:2 geared
you get now 90Watt power
efficience at 60-65%
only 12A current needed..

(comment: its only 90Watt instead of 95Watt, because of the 1:2 gearing i used for the calculation..
so: a little other gearing would be needed)


everything of course without looses of chain, etc. (but should not be that great, a chain runs very efficient)


to sum up:
up the hill, the motor without gear will have 6% more power
but needs for that 100% more current
or other way round:
the geared motor will have ~6% less power, but needs only halfe the current

you see what i mean ?
when you use a overpowered motor, that never comes into the abashment of forced down at fullthrottle to less than halfe the rpm it normaly has at fullthrottle and "low load" efficience-loose compared to geared one is low..
but when you have a steep hill problem becomes bigger and bigger..
then the motor may suck 1000Watt and only 300-500Watt come to the wheel

so my question:
on a steep hill, let say 30%
a motor that runs at flat surface with 25mph will be very inefficient when not regeared for that slope
or not ?

 

[kraeuterbutter]

hope iam not to annoying/cumbrous/importunate...

 

[flecc]

No not annoying at all kraeuterbutter, but I already understand all that and you are avoiding what I posted.

The law does not allow 25 mph, so it's not relevant.

I did say above that with those higher speeds gears would be an advantage so there's no disagreement, but legally we only have a 15 mph limit, and therefore two gears at most is all that's needed as I described. And as said, even that's questionable given the small gain in practice weighed against the complication.

Hub motors in practical usage do the job at close to the same efficiency so there's no point in making things complicated and creating more chances for mechanical failure.
.

 

[kraeuterbutter]

hmm..
in Austria we are allowed to go 25km/h
(in the city thats fast enough in my opinion)

so on a hill speed should not fall much under lets say 18km/h, otherwise the efficience drops into the cellar

gearing: i also think: 2 gears would be enough (one for flat/tiny hills, one for medium to steep hills)

but the easier way seems to be, that the motor uses the already in-use-gears from the bike..

 

[flecc]

but the easier way seems to be, that the motor uses the already in-use-gears from the bike..

I would agree but for one thing. The hub gears which are often used are designed for a rider, and even just used by a rider they fail at times, especially with stronger riders. When used to transmit motor power as well, the failure rate increases.

The Panasonic system used on the current drive through gear bikes minimises that by having low power, but today's customers tend to want more, and those hub gears wouldn't be up to that. The alternative of the derailleur already wears very fast, and that would also be much worse with motor power fed through.

Therefore when judging efficiency, in this and in other matters, I look at the theory in the context of practical application. There's little point in saving tiny amounts of electrical energy when running if large amounts are used elsewhere to provide a feature. A replacement hub or very regular derailleur replacement parts will have cost lots of energy to produce, transport and supply. A motor system like the Panasonic with it's alloy castings, precision shafts, bearings and helical gears costs staggering amounts of electricity to produce, dwarfing what we use.

And when the extra complexity causes the bike to break down and the owner drives his car to work instead - - - - need I add more.
.