What makes an efficient on road e-bike?

[flecc]

To Stuart:

You can't add Lithium cells like that Stuart. In the groups of 7 or 10 cells in a battery, each cell has it's own management circuit, and those are all tied to a master circuit controlling the charge and discharge of the group, the latter feeding the current to the bike. Adding cells would mean a total redesign of the electronics. Too dangerous to run them in parallel either, so those add on options aren't on. See here.

If they had been, I would have definitely gone that route for the Radical battery, but threw out that idea right at the beginning.

You could pack two batteries into a case, but it would probably be too tall and need a manual switch, so they're probably best in two locations anyway to distribute the weight.

To prState:

I think some of the better e-bike frames are like that already, as I think you suspected. That's certainly true of the eZee Torq frame for example, extra strong downtube and fork flexure allowed to take the powerful motor pull, with the rear frame very lightweight.
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[coops]

You can't add Lithium cells like that Stuart. In the groups of 7 or 10 cells in a battery, each cell has it's own management circuit, and those are all tied to a master circuit controlling the charge and discharge of the group, the latter feeding the current to the bike. Adding cells would mean a total redesign of the electronics.

I can see that adding lithium cells to an existing Li battery is ruled out, but I was thinking more along the lines of (maybe, eventually) somehow celling an empty case with Li e.g. the nanophosphate, Fe3PO4 type: designing & building the whole battery into the existing case?

Is that a possibility do you think? Or would that be too dangerous or ruled out for other reasons e.g. insufficient space, or too complex to build? (apart from fact they're a bit costly & may be unsuitable for ebike use )...

whatamistakatomaka! .

Stuart.

 

[flecc]

Building a newer complete design into the existing case would be fine Stuart, a bit like the reverse that Ian and I do in building NiMh into Li cases. But it wouldn't be possible to build from components without electronics designed for it, and no-one is going to do that for a one off.

I'm not at all happy about using the nanophosphate, Fe3PO4 type cells or other newer types independently as someone has posted with model use. The high loadings and long periods of use on electric bikes are a very different case from using a very high current and high discharge/charge rates for cells used for a few minutes on a model helicopter.

The latter is reproducing the same sort of tests that battery development labs use, afterwards publishing the results with the extravagant claims that have let us down time after time in the past and currently with lithium types.
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[coops]

Thanks flecc

What do you think about a small-scale "test" of some of the newer Li batteries, like trying a small, low capacity one just to see? That would also serve the purpose of a stress test to see if even a small no. cells can meet the demand for current required by the bikes?

I'd be a bit nervous about building my own, and probably give up if it was too difficult... but I'd make it a DIY job if necessary .

On the subject, I've seen this site which appears to be advocating li nanophosphate for ebike use, and I hear that Mark at Team Hybrid may be stocking some nanophosphate too?

EDIT: Mind you, given the "quality" issue with some of the Li-polymer...

I know, it would be great if they match their "hype" with good, real performance, but nothing conclusively shown yet, but is there any harm in a little test?! actually, I recall you saying some ebike manufacturers were trialling batteries like these: any news of those? Would that render our own trials unnecessary? (remember what happened on your Q bike with the Lithium ezees...!).

P.S. This is all still in the interest of efficiency John, weight saving & range extending etc.

Stuart.

 

[JohnInStockie]

I think I'd struggle to mod an existing bike, John. is your idea to really design & build an ebike from start to finish? do you really think that's do-able?! (I'm open to persuasion, & no harm brainstorming )

Which type of motor do you think would be best/easiest/most economical i.e. best "bang for buck"? (hopefully no bangs though... )? I guess hub motors are simplest?

Stuart.

Stuart - I am not so sure. I think from what I have seen, that some existing touring bikes do have the right shape to become ebikes, a number of them have 2 -3 inches gap between the back wheel and the downtube, which might be enough for a velcro 'bat-pack' perhaps. Additionally I do not know which would be the better, a rear hub (Puma style ) or a Curry style kit.

Flecc - Yes those prices can be a little high although Wilsons advertise bespoke frames from £250. But I guess that it could easily go to £500+ for a 1-off design (but they do give a 3yr warranty I believe). However, if you were ordering more, perhaps the price would go down some. At the moment though I am still putting ideas together but my basis for budget is 'replacement vehicle for commuting, as apposed to a car', so still a bit of room in the budget even if I had the perfect e-bike at £2000 with its Q-bike capabilities and 36V 50Ah battery at 2.5Kg (but I am hoping it wont go that far - but I think that if the views on this forum had expressed that the swissbee was the best bar none, I would probably be riding one now).


RE the battery
I am not saying that the battery fixing should be frame mounted. I am thinking of a pack either by the panniers, that could be lifted off using a shoulder strap, or a circular velcro pack that would attach around the downtube. Some fundementals though are the gearing must be full range, the motor needs to power the chain or the rear, and it should be made for the efficient use of rider power.

If I am miles off on this, please let me know, Its all a good learning experience.

John

 

[coops]

I was in two minds again about where to post this one, but decided not to overclutter this thread . Its relevant though.

Its all good stuff John, and food for thought. I think hub motors seem more available, affordable and aesthetically quite good: I don't think I could fit my own transmission drive, even if it is more efficient: if one optimises efficiencies elsewhere, then the tradeoff looks better on all fronts: cost, efficiency & ease of build . I really don't think a useful commute bike needs to nor should cost the "earth" - its still a bit of a lottery, and could still be unreliable in so many ways, unless you have the technical skill, experience & understanding to make it durable, and maintain it well too!

I've thought long & hard about battery fixture for ebikes, I even thought about velcro-type battery packs myself John : to me, only light, low-capacity batteries could really be attached to the frame, especially downtube which takes a lot of stress anyway? What do you think flecc? Panniers would make it very back heavy, especially with a rear-mounted currie or hub motor, which could itself weigh up to 3.5kg/8lbs (curries are a fair bit lighter i think, but tend to be noisier), but I don't see much alternative... unless you already have a battery compartment built into the frame like on purpose-built electric bikes .

Yes, its all a learning experience for me too John, definitely! .

36V 50Ah battery at 2.5Kg

I wish!...

Stuart.

 

[prState]

As far as amp hours, put 18 kg of batteries in a bike trailer. Give the trailer its own little motor. Zero weight gain. I don't know about the legality or stability of it all. Of course, all that weight, you wouldn't want to find out by surprise you need better brakes on a steep downhill

It might be easier to buld a motorized trailer to carry lots of batteries, than build a bike from scratch though.

 

[coops]

prState, with a motorized, battery equipped trailer like that, you wouldn't need to build an electric bike; just let it push you along .

I don't know the legality or stability either, could be a bit hairy if you lose control of the trailer though a Grandad cartoon moment?! .

Stuart.

 

[flecc]

To Stuart:

eZee were trialling Fe3PO4 many months ago but still it seems nothing has come of it, and they said the Li-polymer was "terribly disappointing" for their bikes. The fact is that lithium batteries aren't willing to issue demands for high currents, hence the cutting out seen on eZee and now Wisper's powerful models when hill climbing.

Lab tests and promises are based on using very small cells, the sort kraeuterbutter uses in models, and that's very easy to do, since small cells haven't very far to pass current to get it out of the cell. It's when we translate to large cells that the high internal density to contain a large charge impedes the outward flow of current.

Of course we could use banks of small cells in parallel as well as series, but when it came to charging they all have to be dealt with in series rows only, so the switching requirements would be complex, heavy and potentially troublesome. In addition, to keep charge time down to the usual, you'd have to have a charger for each series bank needing charging, so costs would multiply.

I'll look separately at your last posting Stuart.


To John and Stuart:

A simple solution to frames is to buy a strong 700c frame (28" wheel) and build the bike around 24" wheels. Then there'd be as much as a 5" gap ahead of the rear wheel for a battery. You wouldn't have a "poke through" facility like the eZee bikes, it would be like the Twist's space, but would be entirely practical. You'd need to choose a frame/bike that had good crank to ground clearance, and perhaps use shorter cranks. I use 160 mm instead of 175 mm on my Q bike for example. The front wheel could remain larger which would help with ground clearance if necessary.

To prState:

The snag with trailers is they are very inefficient regarding rolling resistance. Two extra wheels, usually of small diameter, and a large drag is added. I ride with a large goods trailer a lot, but whenever I can get a load onto the bike only, I always prefer that option, so I think that's always preferable for batteries.
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[flecc]

prState, with a motorized, battery equipped trailer like that, you wouldn't need to build an electric bike; just let it push you along .

I don't know the legality or stability either, could be a bit hairy if you lose control of the trailer though a Grandad cartoon moment?! .

Stuart.

There's one pushing trailer for bikes, trikes and recumbents already on the market. It has the motor and battery in the lower half, goods space in the upper half. From the Dutch Cab Bike company:

No problem with legality. UK laws with only one exception refer to "bicycles, tricycles, and bicycles with four or more wheels.
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[flecc]

To Stuart:

Re: your last post I referred to. On the link you asked if there was any reason why such a high geared motor was used for the Torq. That's one I've explained many times. It's the Quando motor, designed for 20" wheels, so when put in 28" it's geared up 40%. Not design, just using an existing component. If the gearing was changed to normal it would only run to legal speeds so there'd be no point, just duplicating what existed already in the bikes with the Sprint motors.

I've already given an answer and possible solution to the frame in the posting above to John and yourself.
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[coops]

Thanks flecc

I'd better reply here to that, now .

from here:

28" just seems a bit... big! might there be extra strain on or losses through the spokes at that diameter? I just can't help but think there's something intuitively amiss about hubs in 28" wheels? Though I suppose the Torq works quite well, is there maybe a reason why it was made with a highgeared motor...?

I didn't put it very clearly, I meant, in the context, was there possibly some reason why a relatively "low torque" motor - given its high-gearing in the 28" wheel - was used i.e. not just to use an existing component to make a fast bike, but to avoid using a higher torque motor within 28" wheels, though point taken that if so it would have been a 28" "sporty" looking sprint instead!

EDIT: I just re-read your last post:
When you said "Not design, just using an existing component" is that the answer, that 28" need not be precluded from "normal" geared hub motors for legal speed & low-speed torque on grounds of torque affecting the large wheel size adversely? It seems a difficult question to frame, sorry still don't think I've put it right...

Stuart.

 

[flecc]

In theory any wheel size is fine, but as you mentioned previously, spokes play a part. There comes a point in applying power when heavier components are needed, like using a moped type wheel. At that point it's self defeating for a pedal bike, so I think 28" wheels using cycle components with a powerful and high torque motor is probably undesirable. Best stick to 26" or smaller. After all, that's what the bike-like mopeds from Honda and others do, use smaller wheels.

As for using a higher power motor for the torq, it wouldn't have been conceived as a model. It came into being solely because eZee had seen the power of their existing Quando motor and thought it a good way to further exploit it. My comment in the Q bike introduction on the difference in philosophy applies here, my exploiting the motor in a better way by keeping it's gearing correct and adding to it's capabilities with multiple cycle gears and high bike efficiency.
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[coops]

Thanks flecc, thats what I suspected. Does that rather put the "kibosh" on the Puma, geared for 28" wheel, then? Unless sufficiently strong spokes etc. are used...? Back to the drawing board?

To be honest I find 26" wheels a more manageable size and prefer them to 28", and the efficiency decrease from 28"-26" in rolling resistance is marginal (with better tyres on 26" wheels, friction may be less than some 28" tyres?). Just need a suitable 26" electric frame to use... then a good motor geared for the wheelsize... could still use the puma for that, just needs a frame can take batteries... .

Stuart.

 

[Grandad]

As far as amp hours, put 18 kg of batteries in a bike trailer. Give the trailer its own little motor. Zero weight gain. I don't know about the legality or stability of it all. Of course, all that weight, you wouldn't want to find out by surprise you need better brakes on a steep downhill

It might be easier to buld a motorized trailer to carry lots of batteries, than build a bike from scratch though.

 

[coops]

Thanks Jeff, thats just how I saw it!

As an afterthought, I had this idea for a battery case.... (hold on lads, I've got an idea... with apologies to the Italian Job!)

No, seriously! It's "all hypothetical" as John said: it was something flecc said the other day about a damped suspension system for an offroad ebike battery fixture. So I was wondering... could a bike frame possibly be strong enough, and could it work, to somehow affix a battery case "suspended" (very stiffly) between, and affixed to, top, seat & down tubes (I think an image would help here... ) such that the attachments to the frame spread the weight stresses of the batterycase over the tube lengths e.g. they could be "tubular" themselves, wrapping around the tubes, and the suspension acts to counteract both vibrations and at the same time assist in balancing the distribution of weight stress by having a stronger push up from the down & seat tube sections to oppose the downward stress on the top tube, for instance, even when the bike is stationary...? Just don't ask me how it would work, or how the bike would handle - how would it affect handling?

Help, I need a diagram!

Stuart.

ADDED: The other battery idea was more aesthetic I think: to build batteries into tubing, then fit the tubing into the frame i.e. to try to integrate the battery "cases" into the frame structure itself? Possibly as a lattice? - could have benefits for stealth & security? - maybe could also be positioned somehow to minimise frame stress i.e. such that the points of highest stress on the frame coincide with the stronger parts of the frame? I think a crash-course in engineering is called for... .

 

[coops]

With 24" rear wheel in 700c sized frame, what would you suggest for brakes flecc? (if the front 700c wheel is retained, admittedly that would just leave the rear...!)

Back to batteries, how about fitting a "sprung" case into the frame along length of seat tube, held in at the top by the top tube & at the base by the down tube, like those pumps one used to get which fitted "into" the frame, held in by a spring? (spring would have to be (strongest?) at the top (?) to avoid "springing" out when you hit a bump/compression! ). not much width to play with though, especially near the crank... could be fitted between the seat tube & rear wheel in similar fashion though? Is this a strong load-bearing point in the frame structure, the weight of the rider goes through here? Seems a good central, vertical & low position for good overall weight distribution & handling, almost an extension of rider weight when on the bike!

Stuart.

 

[JohnInStockie]

Stuart - I think that a touring frame would be able to take the stresses involved as they are specifically designed to carry loads over long distances (I believe from what Ive read here - note what it says about rolling resistance between 700C and 26" wheels)

 

[coops]

Looks useful John: what size frame were you looking at before?; what do you think of flecc's 24" wheel in a 700c/28" wheel frame idea, for bigger battery space in front of rear wheel? The narrow vs wide wheel rolling resistance debate rolls on... but if the tourer/road-adapted MTB is 26", I'm thinking narrower tyres (like on the T-bike) is the way to go?

ADDED: For efficiency on 24" tyres, lowering rolling resistance is more crucial. It may well be easier to find suitably geared motors for smaller 20-24" tyres anyway, so flecc's suggestion on frames is very practical...

Any more thoughts on battery fixture?!

ADDED: I imagine that a battery built integrated closely with the frame could serve a threefold purpose: a stronger fixture, less weight strain (i.e. better weight distribution) on the frame and security (thiefproofing) advantage. Access for removal might need some thought though... .

Stuart.

 

[flecc]

For brakes Stuart, It's either getting a local welding facility to shift the mounting stubs if you can find someone to work with thin alloy tube, or use disc brakes. I don't like discs, but in this case it's Hobson's choice. Discs can be adapted to use with a motor, and Heinzmann's have been sold with a very large disc.

If you kept to a 700c wheel at the non-motor end, only the motor wheel would need a disc. Another approach is to use the dodge that the trike manufacturers use, both brakes on one wheel. The law only demands two brakes, it doesn't say they must be on two wheels. So you could have a hub and V brake on a wheel, or on a front fork, V brakes at front and rear of the fork crown.

Springs are not a good idea for carrying batteries, they flail about hopelessly unless they are heavily damped, and the total weight of a fully damped system would be high. A strong foam rubber is better, lining a battery mount or case, but best of all is viscous fluid damping, though that would still need centering springs as well and could also end up heavy. Starting from scratch, for an all terrain bike, it's best to have a mid motor and battery on a bike with full suspension.
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