Human/Electric hybrid velomobile?

Jeremy Harris

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Oct 23, 2007
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Location
Salisbury, UK
I've stuck a 405 hub on the front of my recumbent (which works well), but have now come to realise that my "pedal power" input is very much more variable than I thought it would be. Because a 'bent tends to freewheel down even slight hills pretty fast, there are plenty of occasions where I'm not pedalling at all.

I've thought about regeneration, but this isn't really the best answer (IMHO) if, like me, you want to try and keep fit. Ideally I would like a bike that allowed me to always pedal at a comfortable rate and power, up hill and down dale, with the electric system making up for the peaks and troughs in demand.

I'd also quite like some weather protection (I live in England......) so my thoughts are turning to a very light, composite monocoque, velomobile trike. I don't want masses of speed, just enough to keep up with urban traffic, perhaps 20mph to 25mph average speed.

So, this has led to the idea of just connecting the pedals to a generator, perhaps another brushless hub motor connected as a three phase PM alternator, suitably geared up. If I pick the right motor, I should be able to get enough out of it to charge the batteries at maybe 50W - 60W average (about 80W input power from the pedals). The advantage of doing this is that the structure is simpler, as the generator can be inside a central spine, just behind the cranks, with a simple direct chain drive.

I reckon that a decent high power rear hub motor, plus a 48V, or perhaps 60V, battery pack would give the performance I need, provided that I can keep the weight down. I've experimented with a light weight composite aircraft fuselage, using strip plank balsa and epoxy glass (a boat building technique, see here: http://www.storerboatplans.com/Balsacanoe/Balsacanoe.html) and this looks like a good way to get a strong, yet light, structure. I'd plan on using a hollow composite spine and cross member to provide the necessary structural stiffness for the "pilot", wheel and crank forces. The fact that a long chain, gears etc are not needed should compensate in part for the weight of the generator.

Even though such a hybrid system is obviously of poor direct efficiency, the fact that it would allow continuous power input by the rider to top up the battery, even when careering downhill at full speed, or whilst sitting still in traffic, would make up for some of the losses. Being able to put perhaps 20% or so of the power used back into the battery all the time might make this concept as efficient as a conventional pedal direct drive/electric assist system over a long run on hilly terrain.

I'm guessing that someone has already tried this, as it's not exactly a new idea, but also suspect that many people have discarded the idea because the direct efficiency is low.

The final advantage, here in England at least, is that I may well be able to keep this "sort of" outside the registration, road worthiness test, etc rules, as I'm hoping that I can argue that it's still an "electric assisted pedal cycle" (although I'd have to perhaps keep the speed down!).

Any thoughts?

Jeremy
 
Thanks for the link, Miles. As I guessed, others have thought this through in a similar way!

It looks promising, provided that the weight can be kept down. I've just done a stack of runs using the bike power calculator website and it does look like the concept would work well in a very light, streamlined velomobile.

I've plotted some graphs of power vs speed from the website calculator, then overlaid the power vs speed plot at 48V for my present 405 hub motor on a 20" wheel. This looks like it would give me about 10mph on a 10% gradient (nil wind), 25mph on a 5% gradient (nil wind) and about 33mph on the flat. I reckon that if I was to run it up at 60V it might well just about do the job, but that then creates a bit of a problem with the generator, as it will be a bit harder to get 60V from an easily available PM motor run as an alternator.

I'll do some more thinking and see what pops up.

Thansk again for the link, it's given me a couple of useful leads.

Jeremy
 
a 12 pound canoe? Impressive. I wonder just how light a monique Velomobile could be with a Balsa core, but a carbonfiber laminate.


The Idea sounds great, and has been kicked around on here before, but there are a couple problems that come up. First, generator is only going to be around 80% efficent, meaning every 100 watts of power you put into the peddals is only 80 watts out the generator. Then there's the conversion from the generator's output to the battery through the charger and BMS, which is anywhere from 50% to 80%, but we'll be optimistic and say 80%, meaning of the original 100 watts from your feet, 64 are now stored in the battery. But the drive motor is only about 80% efficent as well, and only at its optimum running speed, so at that point only 51 watts of your original 100 are getting to the pavement, and thats only when everything is at the optimum.

What that really means is you are losing 49% of your potential energy over having NO generator at all, and simply pedaling along with the motor.

What you can do to fix this is to build a jack shaft, that works by letting you shift between driving the rear wheel directly, and driving the generator. That way when the motor is struggling, like up hills and while accelerating, you would be peddling along with the motor in direct drive mode, but when you reach a downhill, or a point were you normaly wouldn't be peddling, you can swap over and be charging the battery with the generator.
 
Drunkskunk said:
What you can do to fix this is to build a jack shaft, that works by letting you shift between driving the rear wheel directly, and driving the generator. That way when the motor is struggling, like up hills and while accelerating, you would be peddling along with the motor in direct drive mode, but when you reach a downhill, or a point were you normally wouldn't be peddling, you can swap over and be charging the battery with the generator.

IMHO a simpler way to do this is to get a regenerating controller for a hub motor and implement a cruse control system that combines throttle AND regenerative braking. Wouldn't help at a stop-light though. Maybe a big lever to lift the rear wheel at stop-lights?

Hm... another system that could keep working at stoplights would be to have a motor/generator with a regenerating controller driving the bicycle cranks. Now driving at a constant throttle (this assumes the controller uses synchronous rectification and regeneration just requires reducing throttle a bit. A DC motor and a http://www.4qd.co.uk/ control would do this) simply adjusting pedaling cadence a bit would switch from assist to regen mode. (pedal slower and the motor helps out, pedal faster and the motor charges the batteries) Hm... looks like a simple idle "gear" wouldn't work because a bike tranny needs to be spinning to change gears. A lever to lift the rear tire would still work at stop-lights.

Crazy idea man,
marty
 
I've been working through all the efficiency issues to try and see how they stack up in the real world. It'd be great to improve on the inherent efficiency of the motors, generators and batteries we have, but as I'd like something practical to build, I'm stuck with the sort of 80% figures quoted.

Although the direct efficiency of a pedal - generator - battery - motor series hybrid is low, there is some compensation. It seems reasonable to guess that I can pedal at around 80W for long periods without too much hassle, which means that perhaps 40W of usable power gets through as available motor power.

From the bike power calculator website, it takes about 160W to power a streamlined trike at 25mph on the flat, so I'd be contributing maybe 25% of the power required (maybe a bit more, as in this case power isn't being stored in the battery, but is going direct to the motor). As soon as the trike starts going down hill, even at a very slight gradient, the power demand falls quite steeply (a 1% downhill gradient only needs about 26W for 25mph). In this case I'll be charging the battery by a small amount. A steeper gradient, say 2%, starts to give a regenerative benefit (as long as the controller can handle it) of around 112W at 25mph, which will be added to the 40W of pedal power generation, giving a total charge of perhaps 150W. Yet steeper hills just rapidly increase the amount of charge available.

As soon as the trike starts to go uphill things get bad pretty quickly, as the motor needs to draw a bit more power than a bike with pedal assist. According to the power calculator, the motor needs to deliver about 1540W to maintain 25mph up a 10% gradient, and 854W to maintain 25mph up a 5% gradient. From what I've read, direct pedal power from a non-athlete (like me) will max out at around 200 - 300W for a very short burst, so even with a direct pedal-to-wheel drive the gain over using the generator system is quite small, maybe 12 to 15% overall.

This small loss of hill climbing efficiency might well be compensated for by the extra power stored when going down hill or when stationary or at low speed. Either way, the concept does seem to be worth looking at, particularly if I can engineer a streamlined trike that is very, very light.

Does anyone know what the maximum safe voltage that a Crystalyte 36V-48V, 35A, controller will take? I've read that the FETs are good for 100V, but will the controller take 60V OK?

Thanks for the tips and links, I've spent virtually the whole afternoon chasing "series hybrid" links and playing with spreadsheets.................

Jeremy
 
Some have run the stock controller up to 72v with no problems. They tend to blow up above 48v though. Using higher resistance wire from the motor to the controller will help prevent overcurrents, but the added resistance wastes power.

A disruption of the hall signals while at speed may cause destruction also. Make sure those hall connectors and wires are secure.

If it blows up, it needed 4110's anyway.

I'd like to see how it works out. It would be like having a CVT. In fact, it may be about as efficient as a Nuvinci hub under some conditions. The ability to add power at ridiculously high speeds could be an advantage.
 
Hi Jeremy. In reading about your plans, the following sentence stood out:

From what I've read, direct pedal power from a non-athlete (like me) will max out at around 200 - 300W for a very short burst

I have questioned how my meager contribution could make any real difference. I was using three hub motors (trike and trailer) at 36V with 35 Amp controllers for an estimated 3500 +or- Watts total. Now I am using only two hub motors (trailer only) at 48V with 35 Amp controllers for an estimated 3000 +or- Watts total.

However, the hill I have to climb to return to my home exceeds 15% grade. If I don't pedal at all, the speed starts dropping, and at about 7 or 8 MPH and still dropping I can't stand the thought of letting the smoke out of the motors, so I resume pedaling and bring the speed back up to my normal hill climbing speed of 11 or 12 MPH.

For what its worth, the two motors with lower total Watts perform slightly better than the three motors. Some of this improvement may be because it is about 20# lighter.

So my point is, before you make a bike or trike that you can't apply direct pedal power to, make sure it will climb the hills you expect to encounter on a regular basis.
 
Howdy and thanks for the link to my boat plan site.

I have done a lot of work with lightweight structures both using plywood and more complex building methods like the balsa strip.

In general plywood can be almost as light. It may not be cheaper in material terms, but it would be cheaper in labour terms - ie faster to build!

It also allows a number of different prototypes to be built quite quickly - and then maybe when the main design issues are resolved move to something more sophisticated like the balsa strip.

As an example the plywood Moth Dinghy hull here would enclose a similar volume to what we need for a recumbent but carry much more surface area because of the flattened shape - the typical weights of wooden hulls in this era were around the 30 to 35lb mark in final form before the boats became really thin. Remember that this is a structure that carries concentrated loads 4 times greater than the weight of the sailor.

lee.jpg


The main thing is to design in lots of curves, that way the plywood will be self supporting rather than requiring extensive and heavy framing.

Maybe too there is a weight economy in realising that the timber structure is actually better at sustaining loads than the tube structure of the bicycle, so at some point it becomes sensible to start eliminating the bicycle frame component. This is not because timber is better, but because the timber version is wider and deeper.

Additionally having the bodywork can reduce the aero drag component which will reduce the power requirement for a given speed. YOu can always open an umbrella if the wind is from an advantageous direction!

Do you have any base dimensions and layout for the recumbent that you are talking about?

Food for thought - and an interesting discussion.

Best wishes
Michael[/img]
 
Rassy,

I'm not sure, but think that the most probable reason that your pedal contribution makes such a difference on hills may well be down to the very high torque at low speed that your efforts can provide. Maybe the hub motors simply don't have enough torque when it comes to hauling slowly up the steep gradient? It's a good point though, and a compelling argument for direct pedal drive at low speed.


Michael,

Wow! Thanks for the contribution. I first spotted your balsa strip plank technique about a year ago, and adapted it to make a small experimental microlight fuselage pod. What appeals to me is the ability to get a very fair 3D curved structure without masses of effort making moulds.

My ideas so far are for an internal cross-shaped composite box frame, that will hold the rear wheel swing arm attachment at the back, the pedal/generator at the front, the front wheels at either end of the cross member (most probably on aerofoil section composite spring "axles", similar to some I've already made for aircraft) and also distribute the load from the riders seat into the hull.

I envisage the hull being as narrow as I can reasonably make it and just tall enough to allow the use of the shortest cranks I can lay my hands on. I don't plan on fitting an enclosed head cover - it's safer to be able to hear well in traffic. Unlike the outright performance streamliners, this has to be usable as daily transport, so needs to tall enough to be safely seen in traffic, so I don't intend to have a really laid-back posture. Similarly, I may sacrifice the ability to travel on narrow cycle-only paths by using a wider wheelbase than some lower trikes.

My target weight is 30kg, of which the hull may be around 10kg. Most of the weight is in the motors, batteries, cranks, chain etc. The wheels will be 20" all round, with the exposed front wheels perhaps fitted with disc spoke covers (if it's worth the hassle). Hub brakes look like a sensible option for the front wheels, simply because they're easier to fit to a stub axle system.

Overall length looks like it has to be around 2.5m, with a hull maximum beam of about 0.6m. I've developed a shape that might work, using a symmetrical aerofoil section with a wedge shaped insert down the centre line to make it taller than it's wide.

Masses of work to do yet, including the vital decision as to whether a direct drive "granny gear" is a necessity. I'm leaning towards this being essential after reading Rassy's post, plus it would provide a get-you-home capability if all the electrics failed. I'll have to find a way of doing this at minimum weight though.

Thanks for all the useful input.

Jeremy
 
Howdy Jeremy,

One of the disadvantages of an airfoil shape is that it is designed to provide lift when the wind is anything but straight on. A more wedgy shape is often more directionally stable in slight crosswinds but you don't want a sharp vertical prow like a boat either. slight variations in wind direction either side of central reverse the aero forces suddenly and dramatically when the nose is sharp. My sailing canoe is a real wild thing on the car roof with the razor sharp bow forward, but the pointy stern has a 19mm flat on the front and when the stern is forward it is relatively well behaved.

So wedge/pointed with a "sensible" nose radius to make the reversal of forces with reversal of wind direction more gradual.

The single rear wheel begs a pointy stern or to just have it open after the rider support.

I know about the ears - I shudder when I see people wearing headphones when riding. Good to sneak up onto when I am driv ... ooops

would be good to see a pic of the fuselage you built?

MIK
 
MIK,

My other hobby is aircraft design, see http://www.realityaircraft.com for one that I helped design years ago, or the attachment that is my current project (the one where I built the test section fuselage from strip plank balsa - no pics yet I'm afraid, I broke the test section.......). Curiously, I also restored an old yacht about 20 years ago, a 22ft LOD gaff cutter, pitch pine on oak, carvel hull. The restoration took four years, after which I vowed never, ever, to feel sorry for an old wreck of a boat again. Having said that, she is still sailing today, nearly 100yrs after being built, so perhaps the effort was worthwhile to preserve a bit of history.

I agree that getting the aerodynamics right is important, both for low drag and to ensure that the effect of crosswinds is minimised. This is easy enough to do with a bit of calculation, the main thing being to ensure that the aerodynamic centre is always slightly behind the lateral C of G, so that any cross wind component will tend to turn the bike into wind (pretty much like the balance between hull, keel and sails in a boat to give a bit of weather helm).

Unlike a boat, a velomobile can have a "fat" nose radius without having any serious effect on drag; most of the drag will be from flow separation towards the rear of the hull, so ensuring that flow stays attached well aft will be key to getting the drag down, particularly as the Reynolds number at typical bike speeds will be very low, well down into the region where laminar flow rules supreme, unlike a similar sized boat, where I doubt that any of the hull surface flow beyond about the first quarter of the waterline length will be truly laminar.

I quite like the idea of using ply, but the little bit of artist in me is yelling for super-smooth curves. Given that laminar flow is needed, this also argues for having smooth curves. I have looked at using narrow foam planks as a core, and picked up a pack of cheap 1/4" thick EPS foam floor insulation from the local DIY store. I may have a play at hot wiring some of this into thin strips and see how it goes.

I've also been giving some thought today to the reason that adding pedal power makes a real difference on a very steep hill. From what I can gather from searching the web, it looks as if a reasonable figure for torque at the BB is only around 30Nm. This gives around 12 to 15Nm at the rear wheel, whereas my 405 hub motor on 48V should give about 32Nm at 10mph. I'm guessing that the rider can give a pretty constant torque for a modest cadence range, whereas the motor torque drops rapidly with increasing rpm. Either way, pedalling can clearly increase the available torque by a substantial amount, although this clearly reduces as the rider changes to higher gears.

One option may be to have a fixed low gear for hill climbing, with the generator and fixed gear all on a common chain. With a freewheel this would allow pedal effort at low speeds, but as the velomobile speeds up the rider would only be pedalling the generator. This still keeps the weight down, and also allows the drive chain to be enclosed, allowing it to stay clean and well lubricated.

I can see that I am going to have to clear out my workshop an make way for another project............

Jeremy
 
Howdy Jeremy,

for discussion's sake only - not being prescriptive.

The picture that started occuring in my head was to do a floorpan of very thin plywood to take all the structural loads - seat integrated into the pan.

The moth sailing boat above use .7mm with 1.2mm in the cockpit area - common for this type of boat. The thinner of those thicknesses requires expensive aircraft ply, but the thicker can sometimes be available as a exterior "bending ply"

Maybe a box section down each side for more width - wonder what the width could come down to? Or a single box section with the seat integrated in the top.

Sides of either could be quite free form to any aero or non-aero section required.

A fancy canopy/top could be added for flows - laminar turbulent and stalled.

MIK
 
MIK,

This sounds like a good idea. If I've understood you correctly, then what your suggesting is a sort of shallow, boat hull like, structural floor pan, built up from thin ply, that carries all of the structural loads. The rest of the hull could then just be a very light fairing, perhaps removable, or hinged, to allow easy access.

If I remember correctly, weren't the early Moth hulls made from cold moulded ply? Such a technique, using thin strips of veneer (or perhaps very thin ply) laid diagonally over a frame mould might well be worth looking at. It's years since I've done any boat building, but I've no doubt that using modern materials techniques like this might just produce a very stiff,strong and light structure.

As an eco vehicle they'd be a certain attraction in leaving the timber clear finished. I remember seeing some old cold moulded dinghy hulls years ago that were real works of art. I quite like the idea of this.

I reckon another session of web surfing is in order to catch up on boat building techniques!

Jeremy
 
Jeremy Harris said:
MIK,

This sounds like a good idea. If I've understood you correctly, then what your suggesting is a sort of shallow, boat hull like, structural floor pan, built up from thin ply, that carries all of the structural loads. The rest of the hull could then just be a very light fairing, perhaps removable, or hinged, to allow easy access.

Yes - With the box members to the side it would provide a sill and some sort of protection and a lower centre of gravity. It may be possible to integrate the top within such a schema.

If I remember correctly, weren't the early Moth hulls made from cold moulded ply? Such a technique, using thin strips of veneer (or perhaps very thin ply) laid diagonally over a frame mould might well be worth looking at. It's years since I've done any boat building, but I've no doubt that using modern materials techniques like this might just produce a very stiff,strong and light structure.

Correct, "mouldie moths" but the flat ply ones were a close approximation and were initially cheaper, but finally faster and much lighter (less than half the weight as plywood allows much thinner skins of course.

Generally strip planking has overwhelmed cold moulding - veneers are harder to get, thin membranes are easier in strip and the strip likes to go fair - unlik a 1/16" veneer or three.

As an eco vehicle they'd be a certain attraction in leaving the timber clear finished. I remember seeing some old cold moulded dinghy hulls years ago that were real works of art. I quite like the idea of this.

Exactissimo! Marketing, marketing, marketing. Particularly if the result is very cool looking!

I reckon another session of web surfing is in order to catch up on boat building techniques!

Jeremy

Maybe - but the problem is all the development has gone to carbon etc - at high cost for a slight weight advantage - maybe some improvement of reliability. But look at the eco cost in energy terms - you would have to do an AWFUL lot of cycling to make up for that CF structure that weighs perhaps 15% more in timber!

The plywood building techniques peaked in the mid '80s and basically I copy my structures from that period - and occasionally do a bit of development like with the balsa canoe to see just how far you can go with particular types of structures.

All good fun.

Michael
 
Michael,

During lunch today I did a bit of digging around on the web and came across this: http://home.clara.net/peterfrost/tryaneii.html.

Isn't that just beautiful?

I just love the curves and wood grain on that car, it's exactly what I have in mind for an eco velomobile finish.

My cousin had an old wooden chassis Marcos many years ago, so clearly this is a fairly well-proven, if slightly quirky, approach.

I've no idea if such a thing could ever be marketable, as the production costs would be way too high, but I guess that as a self-build project, maybe from plans, there might be some interest. This idea appeals more and more as a way to do something very individual.

Jeremy
 
I've been having more thoughts on this.

I have a Prius, which has a limited engine rpm range, essentially just five stepped speeds at it's most efficient, as it uses a modified Atkinson cycle. On it's own, this engine would not be driveable, due to it's poor power delivery curve. In many ways this engine is just like the limited range of pedal cadence we feel comfortable with.

The reason we need gears on a bike is because of our limited efficient pedal speed range of between 40 and 90 crank rpm. If we can keep our pedal rpm at around 60 to 70, then we are more comfortable (unless we're like Lance Armstrong with his 100rpm cadence......), which is why we seem to like closely spaced, multiple gear set-ups.

Even a lightweight composite velomobile, with it's added weight over a bike, will make hill climbing difficult without fitting lots of gears (or a motor). The advent of electric motors eases this problem, albeit with the addition of more weight. Adding gears to a velomobile adds a lot of complexity, as the drive system is less than optimal anyway, due to the length of the chain, idlers etc. A direct drive chain can be very efficient, especially if the chain can be kept straight.

It could be that I could get by with a motor and just two widely spaced gears, one for hill climbing and one for high speed cruising, with the motor providing the necessary extra torque when required, just like the Prius system. There is a neat two speed crank available, the Mountain Drive, that is effectively a direct drive chainwheel that can be connected via a 2.5:1 reduction drive by kicking a crank mounted button.

Such a system might just be ideal, as I could have something like a really tall 120 inch gear for high speed cruising, yet by kicking a button I could drop this to a 48 inch gear for helping with the steep hills. My guess is that I could probably ride most of the time in the taller gear, with the motor making up the difference.

I need to keep the option to pedal to keep the thing legal, otherwise I'd just bin them and go all-electric!

Does this sort of make sense?

Jeremy
 
Many thanks for this, Miles. It looks like someone has had this idea before me! Still, at least it shows that it has some merit.

I agree about the lack of an inverse Speed Drive, that would really be better, as the 2.5:1 jump of the Mountain Drive is a bit much. It would be possible to use the Speed Drive as is, but the snag is that the efficiency in top gear would be a bit lower, due to the gearing losses.

Jeremy
 
A couple of wooden velos.
 

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Brilliant!

The one in the lower pictures is parked next to the wooden car I linked to earlier, which means it has to be here in the UK somewhere. It looks like it's made using "stitch and glue" ply, like some small boats.

I shall do some more digging and see what I can find - I already have a contact who used to know the chap that built the Tryane wooden car pictured.

Cheers,

Jeremy
 
In regards to the cost of carbon fiber-- i believe it's really cheap if you buy just the fabric and the resin separately; it only becomes really expensive if you are paying a skilled worker for the time required to turn it into something useful. I mean carbon fiber ain't cheap compared to cotton cloth, but a frame's worth of carbon fiber fabric+resin costs a pittance compared to a good electric bike system.

I'm not sure, but think that the most probable reason that your pedal contribution makes such a difference on hills may well be down to the very high torque at low speed that your efforts can provide. Maybe the hub motors simply don't have enough torque when it comes to hauling slowly up the steep gradient? It's a good point though, and a compelling argument for direct pedal drive at low speed.

I think that if you're just in shape from regular biking (not a racer type person or extreme distance rider or anything) you can pedal at 180W or more for an hour or so. In my experience, there is no way a 500W motor dwarfs human power as much as it would if we were all pedaling around at 100W of steady output.

I think that unless you are extremely committed to the idea of steady pedal resistance you should think along the lines of a velomobile with electric motor and chain-drive pedals... one you won't pedal at stoplights.

I think that humans are more suited to varying levels of physical effort instead of purely constant effort, so stopping your pedaling for stoplights doesn't seem like such an issue to me. If your bike is designed around only one electric motor it will be lighter, which will help on uphills. If it's a velomobile with good aerodynamics, it will already be extremely fast downhill, (which may help you get uphill on the other side).

All in all, I think an electric velomobile is a great idea, but in one sense it has a disadvantage over the regular electric bike-- it will require more power or lower gearing uphill (if it can't use its aero advantage to just use momentum to carry it uphill) and you'll be more likely to want higher gearing available for flat ground to take advantage of higher possible speeds. Best way to take advantage of that might be a lightweight motor that makes use of your gearing like this one does.
 
cerewa said:
I think that humans are more suited to varying levels of physical effort instead of purely constant effort, so stopping your pedaling for stoplights doesn't seem like such an issue to me.

If your bike is designed around only one electric motor it will be lighter, which will help on uphills. If it's a velomobile with good aerodynamics, it will already be extremely fast downhill, (which may help you get uphill on the other side).

it will require more power or lower gearing uphill (if it can't use its aero advantage to just use momentum to carry it uphill) and

you'll be more likely to want higher gearing available for flat ground to take advantage of higher possible speeds.

Best way to take advantage of that might be a lightweight motor that makes use of your gearing

I'm so impressed by these points that I wanted to repeat them!.

Some capacity to recharge when the power requirement is low is clearly useful.

I know that some electric cars use braking forces to generate electricity when stopping and then use the generated power to reaccelerate so momentum is not completely lost. Are such systems available in bike sizes? I imagine the cost would be prohibitive.

But it would mean that excess pedal torque would be changed into current as well?

Sorry this is a bit garbled - it is new territory for me.

Best wishes
Michael Storer
 
Boatmik said:
I know that some electric cars use braking forces to generate electricity when stopping and then use the generated power to reaccelerate so momentum is not completely lost. Are such systems available in bike sizes? I imagine the cost would be prohibitive.

But it would mean that excess pedal torque would be changed into current as well?

Sorry this is a bit garbled - it is new territory for me.

Best wishes
Michael Storer

Yes, that could be done. It would be a form of regenerative braking.
It would be fairly complicated to implement, since you'd have to drive the motor from the wheel, which would normally be disconnected by a freewheel. The gearing would need to be capable of transmitting power both ways. With a direct drive hub motor, it would be much easier.

The other complication is getting a controller that can do regen at a controlled level. I don't know of any on the market that can do that. It's certainly possible to do.
 
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