Hybrid Bicycle

[dtmpower]

This idea came to me whilst enjoying the bank holiday sun (on set of sun stroke?) Would it be possible to power an electric bike from the current produced from the rider pedalling a dyno/generator ?

So lose the conventional chain drive and have 2 'motors' one making power and one converting electricity to forward motion.

I thought you could have a bank of batteries or capacitors to smooth out any power supply.

What power output would an average cyclist be able to produce over long periods ?

[shalmaneser]

While you were thinking did you also consider the additional weight, complexity and most importantly conversion losses?

[mybrainhurts]

Aaargh...electric bicyclists. They look like ghouls, wafting along with little or no effort...

Fair give me the wobblies, they do...

[anonymous-user]

I'm pretty sure that pedalling/chain/gears is about as efficient as it gets converting power to motion. If a motor could come close you will then be losing out due to the extra weight/cost/complexity as others said. I expect a mathmatician will be along to give the figures!

[paranoid airbag]

I don't have figures and aren't quite a mathematican - except that good fixed gear drive systems (i.e. actual track bikes) deliver over 99% of the crank energy to the wheels, which no electrical setup could hope of rivalling, but I expect you'd really struggle to make any electrical setup that isn't noticeably worse than even a hub gear. Although it could potentially be very low maintenance I guess (and useful on hills, you could pedal down one and have all the energy stored for the uphill instead of used to swirl air around).

Even if you did, there's a legal problem: it would be classified as an electric bike, and the motor on an electrical bike isn't allowed to provide assistance over 15mph - so, a top speed of 15 then (I suppose, a law change could sensibly allow the motor to provide up to your current input in the absence of a chain drive, to allow use above 15 but not allow you to store up loads of energy and then unlease 10 horsepower for a few seconds ).

Sounds like a nice 'eccentric' project tho - I've seen a moving treadmill on the 'net somewhere, and the Grauniad ran a piece about a horse equivalent IIRC (because nothing's as 'green' as a hay-fuelled engine, that can't be switched off (more than once), attached to an inefficient drive mechanism, weighing half as much as a Punto )

[dtmpower]

Well, how about pedaling as a means of charging (range extender) for an electric bicycle?

[Hugo a Gogo]

dtmpower said:

Well, how about pedaling as a means of charging (range extender) for an electric bicycle?

isn't that exactly what pedals do? extend the range?

[Engineer1]

Follow the Energy changes round the system, conventional bike does mechanical a hybrid electric would do mechanical to electrical to chemical to electrical to mechanical and some energy will be lost at each conversion. So a hybrid would never be more efficient than a mechanical bike.

[shalmaneser]

dtmpower said:

Well, how about pedaling as a means of charging (range extender) for an electric bicycle?

You mean exactly like every other electric bike? They're just a bit more efficient because the power goes straight to the rear wheel, not in the battery to be used later.

[dtmpower]

Engineer1 said:

Follow the Energy changes round the system, conventional bike does mechanical a hybrid electric would do mechanical to electrical to chemical to electrical to mechanical and some energy will be lost at each conversion. So a hybrid would never be more efficient than a mechanical bike.

paranoid airbag said:

Sounds like a nice 'eccentric' project tho - I've seen a moving treadmill on the 'net somewhere, and the Grauniad ran a piece about a horse equivalent IIRC (because nothing's as 'green' as a hay-fuelled engine, that can't be switched off (more than once), attached to an inefficient drive mechanism, weighing half as much as a Punto )

Engineer1 - I am sorry, the first post was written on my phone with little detail. I appreciate a direct chain mechanical drive offers a very efficient transfer of human effort to propulsion (short of a little bearing drag and heat/sound production)

But

airbag - you've hit the nail on the head. My ramblings last night are a little eccentric.

I like the idea of a void between the pedal input and the motive power. It could also allow for any riding/frame configuration or even two motors, one on each wheel.

And as mentioned above the potential to over pedal to charge the energy reserve (battery or capacitor) and also maybe have regenerative braking with no need for mechanical brakes.

I will pen some more ideas.

[Mr Will]

Pasted from another thread as it is more appropriate here:

Mr Will said:

OneDs said:

So given that IIRC the human powered bicycle is one of the most efficient vehicles there is, can you explain why carrying the extra weight to transfer energy from kinetic into potential and then back into kinetic can be good especially when a 'bent is already meant to provide a more efficient self powered transport platform?

Assuming that there is some form of capacitor or battery the chief advantage would be smoothing out the amount of power demanded from the rider, you could pedal at an efficient constant cruising rate regardless of whether you were climbing or descending, accelerating or braking. Add in regenerative braking to recover the energy you burn off every time you touch the brakes and I can see that it could quite easily be more efficient than a normal bicycle.

The transmission of human power to tarmac is very efficient on a regular bicycle, the inefficiency is in the generation of that power in the first place.

[anonymous-user]

I'd be surprised if you'd get much back on the regenerative side, I don't see there being that much momentum in the system especially on the road where you coast more than brake. And if you applied the system to coasting downhill you'd come to a stop quite easily unless it was very, very accurately adjustable, or so minute a regenerative force applied it would loose any energy gained in it's system.

So as a theoretical exercise: -

This is GCSE level physics but it was so long ago I can't remember if this is right. Lets say your cruising at 30kmh and the lights ahead are red or you are coming to junction.

Stopping from 30km/h (8.3mps) with a mass of 100kgs (for bike/electric system/rider) = 833 kgmps to zero 3seconds would take 12.5m to stop and require a total force of 1250 newtons of force over the 3 seconds of stopping. Delivering coincidentally 1250 joules of energy.

So first question how much force can the regenerative braking system apply and how efficient is it at transferring that energy back into the chemical potential energy?

For arguments sake if the system was 100% efficient we've put 1250 joules of energy back into the system which would give 3.5 seconds worth of 360w power to be reused in the system.

Right so that's is the absolute best it could do, lets take a more realistic approach, you still need brakes and you'll loose 50% of the energy to normal braking, your motor/generator (one in the same) is 85% efficient in and out. So 1250j * 50% = 625j * 85% = 531.25j * 85% = 451.6.

So in a very good system you'd get 1.25 seconds worth of extra kinetic energy for every major braking event.

In terms of a person, Chris Boardman managed 400w for an hour at an average of nearly 50km/h.

Edited by anonymous-user on Wednesday 27th April 13:58

[Mars]

You're right of course. The downhill regeneration would only work if you could apply pressure to a lever to moderate your speed but which "bled" the excess off to the genny. And that wouldn't really result in a lot of saved energy.

And then you've got the extra battery/genny/motor weight too.

However, if you scope all that ^^^ so that it is small enough to *just* get you up "Henley Hill" (for example) then you shouldn't be carrying too much weight around and the advantage of constant-effort pedalling might actually be beneficial. Certainly I wouldn't be done-in like I am after attacking Henley Hill in the conventional manner.

[Mr Will]

OneDs said:

I'd be surprised if you'd get much back on the regenerative side, I don't see there being that much momentum in the system especially on the road where you coast more than brake. And if you applied the system to coasting downhill you'd come to a stop quite easily unless it was very, very accurately adjustable, or so minute a regenerative force applied it would loose any energy gained in it's system.

So as a theoretical exercise: -

This is GCSE level physics but it was so long ago I can't remember if this is right. Lets say your cruising at 30kmh and the lights ahead are red or you are coming to junction.

Stopping from 30km/h (8.3mps) with a mass of 100kgs (for bike/electric system/rider) = 833 kgmps to zero 3seconds would take 12.5m to stop and require a total force of 1250 newtons of force over the 3 seconds of stopping. Delivering coincidentally 1250 joules of energy.

So first question how much force can the regenerative braking system apply and how efficient is it at transferring that energy back into the chemical potential energy?

For arguments sake if the system was 100% efficient we've put 1250 joules of energy back into the system which would give 3.5 seconds worth of 360w power to be reused in the system.

Right so that's is the absolute best it could do, lets take a more realistic approach, you still need brakes and you'll loose 50% of the energy to normal braking, your motor/generator (one in the same) is 85% efficient in and out. So 1250j * 50% = 625j * 85% = 531.25j * 85% = 451.6.

So in a very good system you'd get 1.25 seconds worth of extra kinetic energy for every major braking event.

In terms of a person, Chris Boardman managed 400w for an hour at an average of nearly 50km/h.

Why would you need to lose any energy to normal braking? Your regenerative braking system could be quite capable of doing all the stopping, getting the total up to 2.5 seconds energy straight away. Now lets halve the output rate; after all, we don't need to accelerate like Chris Boardman, plus our own legs will be doing some of the work. We are now up to 5 seconds 180w power. 180w might not seem a lot, but it's probably not far off what the average cyclist sustains.

So we are now at the situation of being able to double the output of the bike for 5 seconds after every 30km/h stop. Probably not very useful on a flat countryside ride, but something I can imagine being very useful around town where you need to be stop-starting regularly.

[Mr Will]

Mars said:

You're right of course. The downhill regeneration would only work if you could apply pressure to a lever to moderate your speed but which "bled" the excess off to the genny. And that wouldn't really result in a lot of saved energy.

And then you've got the extra battery/genny/motor weight too.

However, if you scope all that ^^^ so that it is small enough to *just* get you up "Henley Hill" (for example) then you shouldn't be carrying too much weight around and the advantage of constant-effort pedalling might actually be beneficial. Certainly I wouldn't be done-in like I am after attacking Henley Hill in the conventional manner.

Now we've done stop-starting, lets get on to your downhill-uphill scenario.

Firstly, we don't need a generator and a motor, the motor will function as a generator quite happily if you turn it without a voltage across it; so that cuts down our weight penalty significantly. There is also possible scope for replacing the batteries with capacitors, with are much lighter and faster charging, but I am not sure how much power they can store so we'll ignore that for now.

The big gain in power that you would gain for climbing Henley Hill would not be from regenerative braking, it would be from pedalling on the way down putting power into the batteries rather than forward motion. It will be stored more effectively there than as momentum because it won't be being constantly bled off in the form of increased wind resistance due to the extra speed.

This should mean that by the time you reach the bottom the batteries will be fully charged and ready to help you all the way up the other side.

This logic also applies at any other time when you'd normally stop pedalling; for example at traffic lights. You could come to a stop (using your regenerative braking) then sit there spinning the pedals building up power to be released once the lights turn green.

While I admit that it's probably not a very useful system for cycle racing, I can see some potential in it for touring and commuting cyclists.

[Mars]

^^^ Yes, absolutely.

Incidentally, I've followed Chris's hybrid trike vids on YouTube with interest. Fascinating as it was, I couldn't find a website - I'd love to read a bit more about the design and the thinking behind it all.

[R2FU]

Would a flywheel not be a more efficient way of storing energy in this application (as in F1 where mechanical KERS systems seem to be favoured over electrical) and probably not much if at all heavier overall?

[Mr Will]

R2FU said:

Would a flywheel not be a more efficient way of storing energy in this application (as in F1 where mechanical KERS systems seem to be favoured over electrical) and probably not much if at all heavier overall?

In my book large lumps of metal spinning at extremely high speeds = bad

Possibly do-able on F1 budgets, but not really doable for a DIYer or small company. It also seems more complicated to get the energy into and out of, although I am no expert.

The other advantage to an electrical system is that you could plug it in to charge it before you set off, rather than it being "flat" at the start of every ride.

[Mars]

Mr Will said:

In my book large lumps of metal spinning at extremely high speeds = bad

Hmm... I wondered whether something equivalent to the automotive "spinners" could be employed using some sort of friction or electromechanical clutch. Thing is, it'd have to spin really fast to be of any use other than an initial "urge" which means centripetal forces at play, i.e. you'll never be able to go around a corner.

[anonymous-user]

Mr Will said:

Why would you need to lose any energy to normal braking? Your regenerative braking system could be quite capable of doing all the stopping, getting the total up to 2.5 seconds energy straight away. Now lets halve the output rate; after all, we don't need to accelerate like Chris Boardman, plus our own legs will be doing some of the work. We are now up to 5 seconds 180w power. 180w might not seem a lot, but it's probably not far off what the average cyclist sustains.

So we are now at the situation of being able to double the output of the bike for 5 seconds after every 30km/h stop. Probably not very useful on a flat countryside ride, but something I can imagine being very useful around town where you need to be stop-starting regularly.

You'd have to have a normal braking system as the regenerative braking systems are very poor at applying enough braking force accurately at low speeds i.e they would work well from 30-15kmh but be useless below 15kmh. And you'd need to balance braking across all wheels not just the regenerative braking one.

Also don't forget you'd doubled the weight of the bike at least by adding the motor/batteries/capacitors etc. And you'd never get away with a zero capacitor starting system so it would have to be a battery.

Edited by anonymous-user on Wednesday 27th April 15:25