What makes an efficient on road e-bike?

[coops]

Ok flecc, thanks a million - you're absolutely right & you're a star .

I think I've already learned that getting a "feel" for how a bike "wants" to be ridden can greatly enhance the riding experience aswell as help get the maximum performance from it, and I guess thats the best & most enjoyable way to do it so I guess I'll just get my watts moving & calories burning, but not the rubber .

Stuart.

 

[JohnInStockie]

Although I've given the Powacycle Salisbury solution for range at reasonable weight and cost, there is one thing missing for John.

At just over 290 watts peak power, it's a low powered bike.

To have a more powerful bike with a long range would drastically up both weight and cost.

It makes me think that there may be some sort of relationship between battery weight carried and range and / or hill climbing energy needed. Although the 290W peak isnt a problem if you dont need more, it also means you have to put so much more in when you do.

The nearest to a universal bike yet is the Q bike.

Yes it is. Alround it ideal.

At this moment, the ridable bike is a possibility, or more than a possibility with just a few small changes to the general offering (Im looking at the Wisper with the rear hub here rather than the Torq, although my mind is open).

The range bike is currently impossible. Yes you would want to pedal (otherwise get a moped) but you dont want to be pushing it up any hill and ideally in my opinion the old Twist was the ideal touring range bike, it just doesnt have any range!

If your struggling to understand what I mean by this, then imagine doing one of the sus-trans routes over a few days as a holiday. You would want between 4 -8 hours riding on the bike between charges, and no up hill pushing, but probably mostly pedelec.

Wouldnt that be nice, touring Britain on an e-bike!

John

 

[coops]

Wouldnt that be nice, touring Britain on an e-bike!

Yes, maybe one day John - without kilos of batteries or compulsory recharge stops, long lunches etc.

I still think that, keeping in mind all thats been said in this thread, a modified Torq - perhaps as close as we can get to a T-bike mod without shredding metal, and with a little motor upgrade - is a good way to go for an efficient, nay, performance commuting bike .

On the subject of which, stay tuned! .

Stuart.

 

[coops]

Going back to the idea of a not too heavy "rideable" ebike with good range, mentioned earlier this thread, I have a suggestion on which I would welcome comments:

I'm not keen on the idea of "pannier batteries", but they do seem to offer a simple, if back heavy, means of fixing a large capacity battery setup to a standard bike. So how about a DIY battery "pannier" style setup, attached in a similar way to Grandad's (Jeff's) Twist battery mod but on both sides, and as a single battery (1 single series cellpack in two parts): about 450-500Wh capacity should be good for up to around 40 miles or more (using an efficient motor & wheelsize combination) with pedalling, depending on terrain & rider contribution, and weigh around 6.5-7.5 kg (NiMH), but on a fairly light Alu alloy frame of ~15kg and with a motor of around 3-4kg max, total bike weight ~25kg, just about acceptable? Could have a lighter battery for the same range with more rider effort; realistic for an ebike thats efficient to pedal-only .

Can weight be carried like this or too much/wrong place? Is such a battery setup feasible? I know its not ideal but it might make a fairly cheap & cheerful ebike with good range for long excursions, especially if battery security isn't an issue and if you already have a suitable bike to convert...

I was thinking something like (in 26" wheels and moderate 17-18mph ish top speed) either a crystalyte 409 39V 12+ Ah, or crystalyte 411 , 48V 10Ah.

EDIT: Crystalyte motors idea scratched due to their excessive weight - I didn't know they were ~8 kg each! Forget that! A similar rpm motor & voltage setup may still wotk in principle, but smaller wheel, faster motor seems more efficient.

ADDED:
Additionally, if the large battery were removeable, would it be feasible to rig up a smaller, substitute battery (rack or frame mounted) for short range use, to fulfil John's concept of a 2-in-1 (long & short range) bike, which could also be carried, when using the larger battery, as a small "backup" battery for emergencies?

Any comments are welcome as I said.

Stuart.

 

[flecc]

Perfectly alright Stuart, and my first thought on the new Twist was that the batteries should have been like that. With NiMh, the F size cells with one and half times the capacity could be used, half each side.

Even with a rear motor it should be ok, with the Q I've got the motor at the rear with the battery very close due to the small diameter wheel, and carry big loads in those huge panniers. I've also carried the radical's 5.6 kilo battery on the rack as well and would be happy to carry two spare batteries, one each side. And all on a heavily dished wheel build without a sign of trouble.
.

 

[coops]

I guess its just a matter of practicality & cost then: how easy it is to do, the quality & reliability of the result, and whether you'd have got better value buying a ready-made ebike to begin with, and carrying 1 or 2 extra batteries as you said, but at least you know the quality of the bike you start with this way (and no-one to blame except yourself if it doesn't work!).

From what I've seen, I think most of the parts (motor, controller, batteries) could be had for around £600 or so, add a bit more for the rest (maybe some of the kit could be got from the states cheaper? After shipping,import & VAT costs probably not much difference though?).

EDIT: The cost was based on Crystalyte 400 series motors; I've rejected those due to their weight, so a suitable alternative is needed to do it at that price.

For that though, you'd get an ebike based on your choice of frame & components, capable of ~40 miles or more per charge, at a reasonable weight (25-26kg or so, plus rear rack, battery holder & case etc.) .

NiMH F-cells 36-39.6V (14Ah ?) would weigh 7.5-8kg in total but give 500-550Wh, good for around 40-45 miles with moderate pedalling in mixed terrain and with more rider effort & efficient, economic use of power as much as 50-55 miles, getting close to John's 60 mile range requirement!

Stuart.

 

[Grandad]

I am so pleased with my modification that I have decided that when the Giant battery gives up I will add another rack on the right hand side of the bike. Here is how it will look. To save weight I may remove the 'wings' on the racks.

I have other ideas on how to use the future empty space when the cells are removed from the existing battery box.

Could it be a tannoy or a boom box? ​

Jeff

 

[coops]

Thanks very much for the illustration Jeff, that helps me visualize what I'm planning...

I am so pleased with my modification that I have decided that when the Giant battery gives up I will add another rack on the right hand side of the bike.

The low positioning of the battery weight on your mod looks particularly good for stability : is that a factor in your decision to eventually add a rack on the right too, or do you want to do it to balance the weight?

I think the advantage of making a holder for both sides from the start is that the load can be simply carried by the rear rack by a one-piece frame "straddling" it, and easily secured to it?

Stuart.

 

[richard]

The preceding discussion has been very illuminating for me. It begs the following question : bearing in mind that earlier posts have indicated the Ezee Liv has a very 'peaky' power band ( I assume this means max torque is delivered over a very narrow rev area) at what mph does the Liv motor deliver maximum torque.
Ricgard

 

[coops]

Hi Richard, I'm not sure but I'd guess its around half of maximum rpm similar to the brushless motors; I surmised as you did that "peaky" means over a narrower range of rpm. I'm sure someone else can answer it better if thats wrong .

P.S. Glad you found the discussion helpful .

I have other ideas on how to use the future empty space when the cells are removed from the existing battery box.

Could it be a tannoy or a boom box?

So you're still thinking how to use that space? It would make a good space for a "boom box" speaker system while you ride - you'll be making another battery mod to power them and a USB charger socket for your mp3 player then? Actually, you could use them to play wildlife calls/sounds while you're out riding the tarka trail, couldn't you, and see what turns up in response?

Stuart.

 

[Grandad]

The low positioning of the battery weight on your mod looks particularly good for stability : is that a factor in your decision to eventually add a rack on the right too, or do you want to do it to balance the weight?
Stuart.

Yes Stuart, I do think that the low C of G is an advantage. As for balancing the weight, with the one extra battery presently on the left, surprisingly the bike feels perfectly upright and balanced when riding.

When stationary the offset weight is noticeable but not a problem.

Placing a replacement battery on the right will look better aesthetically and will be simpler than recelling with less chance of a Big Bang if I were to accidentally short any cells.

 

[coops]

...with the one extra battery presently on the left, surprisingly the bike feels perfectly upright and balanced when riding.

Yes, I thought it would be fine, since some carry a heavier ezee battery on one side in a pannier bag with no imbalance . It does look aesthetically more "balanced" over two sides, and the width looks good for encouraging other motorists to give you some serious clearance when passing .

Using a ready-made battery & case does sound much simpler & safer, you're right: I'll look into using two cases to make one battery divided over two panniers .

Stuart.

 

[flecc]

The preceding discussion has been very illuminating for me. It begs the following question : bearing in mind that earlier posts have indicated the Ezee Liv has a very 'peaky' power band ( I assume this means max torque is delivered over a very narrow rev area) at what mph does the Liv motor deliver maximum torque.
Ricgard

If it's typical of this motor type Richard, it will be very marginally lower than a brushless type, but it's still related to the top speed it's geared for. Knowing how eZee's bikes are generally enabled to run at ther legal limit late in their charge, I'd estimate the Liv's maximum torque point as still being about 8 mph.
.

 

[coops]

I was in 3 minds again where to post this; I'll put it here to try not to confuse the Q-bike thread it also relates to, since its mainly about ebike efficiency.

I still think there is something about hub motors, at least the rpm they mostly run at, which makes them more efficient in small wheels.

I'm aware that smaller wheels, e.g. 20" or less, are less efficient due to rolling friction than larger diameter ones (so low friction tyres are even more important for ease of motion), but a wheel half the weight is also twice as easy to accelerate, and the relative increase in rpm with speed is inversely proportionate to wheel diameter i.e. the smaller the wheel, the higher the rpm increase for a given change in speed.

So put a 260rpm hub motor in a 20" wheel (top speed 15mph) and pedal too, and it seems to me the wheel is easier in two ways to pedal into a faster spin speed, which takes a load off the motor & so increases its efficiency & economy, than for a larger wheel. The smaller diameter may also make hill climbs more efficient too?

In the absence of more data on the efficiency of 26" 15mph motor wheels, I don't know if it happens for other sized wheels to the same extent, nor do I know if it depends on the geared reduction ratio of the motor:wheel or if higher torque, slower spin motors also might behave similarly.

The news that, apparently, a 16" wheel bike achieved 48miles with motor & pedalling at an average 13.4mph on a rather modest 266Wh battery (I'm not aware of what type of terrain it was) - thats only about 5.5Wh per mile adds to my suspicion that hub motors tend to make the most efficient ebikes in small wheels. I'm aware that much depends on the particular motor used, its design & its power consumption etc. but I think the same principle may apply?

I would really like to understand the dynamics better, to have more information on whether there is any real efficiency gain, but intuitively I think there could be: this was one of my first impressions from flecc's Q-bike efficiency figures and I was unable to express this idea properly then, but now I think it seems at least a strong possibility. Ok, so much of the efficiency overall could just come from better pedalability of the bike (which flecc has expressed of the Q), meaning less motor use, and this could be the case in the 48 mile test too - I'm not aware how much the motor was used - but it hardly matters where the efficiency comes from, better range is better range .

Easier to carry extra/bigger batteries too, on a low height bike... .

What do you think?

Stuart.

 

[flecc]

As you know Stuart, I don't agree. If the gearing is matched to the wheel size for the same speed, the effort at the tyre/road interface is identical.

Now add to that the incontrovertible fact that the rolling resistance of a larger diameter wheel is less than that of a smaller wheel on everything other than a mirror finish surface and the larger wheel is the more efficient. The opposite would turn the fundamentals of physics on their head.

The acceleration of the mass of a smaller wheel is a red herring on slow vehicles like our bikes since they spend next to no time accelerating, mostly cruising. In addition, the mass difference of a 20" wheel is very little less than a 26" wheel, especially as a percentage of the weight of a motorised wheel when the difference becomes tiny, and on our bikes the 20" wheel can often be just as heavy.

That's because designers commonly make the smaller wheel's rim and tyre wider to compensate for the smaller diameter in order to equalise the tyre's contact patch. The identically motored Quando and Torq are a case of this, the Quando having wide rims and 2.125" tyres, the Torq having very narrow rims and 1.75" tyres.

The relationship of motor rpm to road speed is the same in both cases. What happens between those two is immaterial. It's like the intermediate orbital gear wheels in a hub. It doesn't matter how many teeth they have, they still just transfer the motion.
.

 

[JohnInStockie]

Its a tricky one this. I can envisage both sides, and the science is confusing me.

If we had 2 bikes geared for the same speed, but with 20 and 28 inch wheels respectively, then obviously the 20" wheels are rotating more than the 28" wheels.

Does this mean that :-

1) The 20" wheels require less turning force to rotate once? [EDIT] But slightly more to rotate to cover the same distance as the 28"?
2) The 20" wheels are carrying more momentum due to a higher rpm when traveling at the same speed as the 28" wheels?

Flecc youre the only person with the bikes to qualify this and you say no. But even you said you were more than surprised at the performance of the Q bike.

Could there be something else that isnt being included in the equation (excluding fairy dust )?

John

 

[flecc]

What surprised me with the Quando John was the sum of the efficiency gains. Although I've loads of experience in efficiency matters, I've always chosen bikes that were at least fairly efficient in the first place. The Q bike was the first time I've taken a very inefficient bike and turned it inside out in this way, and that was where the surprise came in. Now I've done something like the same trick with the T bike complete with 28" wheels, the surprise had gone out of it, but there's still been big gains.

I've just this second come in from using the T, and the buzz that bike gives is something else! Same motor, and ride that and you'd be inclined to agree about wheel size.

But no, nothing is missing from the equation, there isn't one really, it's just a straight matter of a chain of physical relationships. As I've said several times, if small wheels had an advantage, they'd be in racing. Also, e-bike producers wouldn't have moved from them as they've done. Yes that's right, look at the development of e-bikes and the earlier models frequently had smaller wheels, 20", 22", and 24", some of those old designs still around today. But today's designers have abandoned them in favour of the more efficient larger wheel, except for folders. Even in the folding bike field, we've seen a marked growth in 20", 24" and even 26" folders, the 16" size hanging on only for portability, primarily in one bike, the Brompton. Those changes have all been for the gain in efficiency.
.

 

[coops]

Ok, thanks flecc: I agree with what you say about the acceleration being a red herring; I needn't have mentioned it except to say that it would make it easier to increase the rpm, the other factor I was considering, if the wheel was lighter, which, as you say, it often isn't!

The relationship of motor rpm to road speed is the same in both cases. What happens between those two is immaterial. It's like the intermediate orbital gear wheels in a hub. It doesn't matter how many teeth they have, they still just transfer the motion.

This to me is the key to the question I raised, and what would resolve the whole thing: does the effect of pedalling a geared hub motor have the same effect on improving the energy efficiency & economy of the motor, for the same "road speed" (different rpm) increase of different sized wheels, both internally geared for the same speed? If, as flecc says, the gears just transfer the motion/rpm increase "geared up" now (because its working in reverse - from the wheel rim to the motor) then the ratio of rpm increase to "internal geared increase" is the same and the effect would be the same for both wheels (except that larger wheels will require less energy due to less rolling friction...) .

This last "if", the gearing up of the rpm increase to the motor via the internal gearteeth, is the only possible "hidden" factor I can see (barring fairy dust!) which, if it doesn't work smoothly e.g. some sort of friction, could reduce the efficiency of one "wheelsize & motor gearing" setup or the other.

If the gearing is matched to the wheel size for the same speed, the effort at the tyre/road interface is identical.

To John: At constant speed i.e. not accelerating the two wheels require the same force to turn, but 28" will need rather less to roll on the road due to less rolling friction. I think the "angular momentum" of the wheel depends on its weight and the speed of a point on the rim, so given the 2 wheels weigh the same and a point on the rim rotates the same speed for both (cf "on road" speed) then I think they have the same total momentum.

Certainly, for the same weight of wheel, the larger will actually be easier to accelerate due to the same energy required to increase the revs while having lower rolling friction losses. .

Hope thats useful .

Stuart

 

[flecc]

And a further answer to that key to the question Stuart is not what you might expect.

There's a freewheel on the motor, and pedalling the hub is completely independent of the motor, in any instance. The rider is just pedalling the hub shell, just as on any bike.

The design usually takes care of the gear efficiency differences. The lower speed motors often have differently radiused orbital structures which evens out the relationship. Here's the much larger diameter Sprint motor orbital:

.

 

[coops]

Thanks flecc, I thought there was something wrong with my reference to the gearteeth etc., of course there's a freewheel...

So, please tell me if I've got this right now: the amount you pedal beyond/in addition to the motor speed (and not necessarily top motor speed, but say a normal cruising motor-only speed of 10-15mph) makes no difference at all to efficiency/economy for different motors geared for the same speed but in different wheelsizes? Phew! I hope so..!

If yes, then I just hope no more red herrings... except with chips .

Stuart.