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Hi all, new to the forum.
With all these electric bikes around, I think it seems a bit inconvenient that you have to charge up the batteries from the mains in advance. Wouldn't it be more practical if you could charge up the battery while going downhill or on a flat, then once the battery's been charged
up you get an extra boost when going uphill?
My idea (I'm not saying it's never been thought of before but it doesn't seem to have reached the market yet. Correct me if I'm wrong) is:
1) a small magnetic generator with a coil and a cog wheel is linked to another cog wheel which is attached to the chainset (or would it be possible to simply attach a horizontal cog wheel flat against the chainset, as it is?).
2) when pedalling, the chain set cogs move and in turn the cog wheel drives the coil inside the generator to generate electricity.
3) the electricity produced is lead via a cable to a battery placed somewhere on the bike (perhaps on the luggage carrier).
4) a small motor takes electricity from the battery.
5) when facing that hard slog up the hill, the motor can be engaged via some kind of throttle control on the handle bar. the control could either control how big a boost you want, or just have an ON/OFF button.
My main question is now: do I really have to have a separate generator as well as a motor or would it be possible to integrate the two into one - a generator/motor combined? Could there be a switch inside perhaps and the whole thing controlled via a microchip?
Anything else that I should've thought of?
Regenerative Braking for Electric Bikes
http://www.ecospeed.com/regenbraking.pdf
This author doesn't think it's very worthwhile in practice. [Wrongfellow, Mar 28 2010]
Pedal-A-Watt
http://www.econvergence.net/electro.htm
Same technology, different application [ceejay, Mar 28 2010]
Copenhagen Wheel
http://www.gizmag.c...le-wheel-hub/13626/
Similar but you need a SmartPhone [ceejay, Mar 28 2010]
http://www.merriam-...m/dictionary/peddle
[hippo, Mar 28 2010]
http://www.merriam-...om/dictionary/pedal
[hippo, Mar 28 2010]
"Sustainable energy, without the hot air" - David MacKay FRS
http://www.inferenc...r/c15/page_90.shtml
"A new car’s embodied energy is 76 000 kWh – so if you get one every 15 years, that’s an average energy cost of 14 kWh per day" [hippo, Mar 29 2010]
"Sustainable energy, without the hot air" - David MacKay FRS
http://www.inferenc...ir/c3/page_30.shtml
"a typical car-driver uses about 40 kWh per day" [hippo, Mar 29 2010]
[link]
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the second law of thermodynamics? |
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Welcome, [ceejay]. Good, clear writing... not sure about the idea. As described, it doesn't seem able to capture any energy when you're free-wheeling down a steepish hill (and probably riding the brakes) - that being the very time when there's spare energy that you'd want to capture. Maybe that's just a longer-winded and less witty version of what [hippo] said. |
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Yes - it's like this: you'll go up just as many hills as you
come down (assuming you eventually come back home) so
we can view any journey you make as a single hill. To get
to the top of the hill you need to give yourself a certain
amount of potential energy. Let's assume the bike's ability
to convert energy into motion (going up the hill) is 50%
efficient and its ability to convert motion back into
electrical energy (this is the energy recovery coming down
the hill) is also 50% efficient. Then, if the battery has
sufficient energy in it to get to the top of the hill, when
you come back down the other side, it will have 25% of
that energy. A bit more will be lost to rolling resistance
and air resistance (especially if it's windy). You'll need to
top up the battery by (a) furious pedalling, (b) hooking the
bike up to the mains, or (c) towing around a massive trailer
with solar panels on it. |
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... which, in turn, is a longer-winded and less witty version of what I said... |
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... less friction losses from the increased paragraph size. |
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What I'm trying to acheive is not that you don't need to pedal up the hill, only that you don't need to put in quite as much effort - the motor would give you a boost of extra energy to make it feel EASIER but you would still have to pedal. |
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True that, about the wasted downhill energy. Maybe I should connect the coil to the backwheel instead of using a cog wheel - but how? I don't want it to rub against the tyre. |
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//the second law of thermodynamics?// |
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You could always peddle as well, you slacker. |
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Of course, the real efficiencies may be lower than that - plus the fact that you've then got to lug a motor/generator and significant battery up the hill, means that it isn't really worth it on a bike. |
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If what you had was a small peddle-powered, electric-motor assisted car, then it might actually be more worth it. Because then you could be charging it up when you'd otherwise just be sitting around at traffic lights etc. |
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[Loris] The generator the Pedal-A-Watt (see link above) is using is not that big and shouldn't be too heavy.
And the battery can't be bigger than the ones used on normal electric bikes - I could probably get a away with something even smaller as I only need a tiny bit of extra power to climb that hill and don't need to store it for very long (once I'm up the hill the battery will start charging again). |
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I'm aware of the fact that adding weight to your bike only makes it harder to pedal when the motor is off BUT I think it would make more sense to make use of the kinetic power that you're putting in anyway rather than having to go charge your battery from the mains in advance, which seems to be the case with most electric power assist bikes around... I'm doing this as a student project so we can assume our route consists of only one not-so-steep hill to go down and then climb up. |
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//student project//
which post-secondary institution and course ? |
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Hey, you could fit a sail which you could blow into, too. |
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there's just no love anymore, look on the positive side....every little bit of energy replaced has to be a positive? |
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[bigsleep] It looks like it's closer to 25%, but still a lot. See the links I've added to David MacKay's excellent (and free-to-download) book. Spread over a car's lifetime the manufacturing cost is about 14KWh but the fuel cost is about 40KWh. |
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How about a bike where the pedals are connected directly to the generator and the wheels are powered by an electric motor. The motor would become a 2nd generator when braking. |
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Losses each way would be around 5%-10% but the rider could pedal at a constant RPM and torque. |
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I imagine it would take a while to get used to riding it though. |
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Edit: It's also worth adding a smallish solar panel, like 10W. Humans can sustain 100W for a while, so riding to school for 30 mins, then parking for 6 hours should give you enough to ride home. |
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why bother with the pedals in the first place? A giant pinwheel (with a motorgen) on a stick could be faced forwards to collect energy while in motion, turned around to dispense energy, and faced sidewards, streamlined, when you don't want to use it. |
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I do hope that's meant in sarcasm... |
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I believe this has merit. It's probably not going to extend the range of the bike much for people who don't pedal. But for people who do pedal, it could harvest enough energy over a few miles to give some power assist up a steep hill without ever having to plug it in. You could also use power to start the bike moving and not have to mess around with derailed gears. |
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If i may, Regenerative braking has been around for a while, but i think i see a simple solution to the idea. |
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Imagine if you will a hub mounted motor that much like many motors can either act as a generator or motor depending on how you connect the wires. I propose you have a low voltage relay set up that switches the function based on whether the gears are engaged when pedalling or disengaged when idling. that way you get power when you need it and generate power when youre not pedaling. mind you that the result will end up pedaling up to speed and if you stop pedaling the drag on the generator will slow you down so on a flat surface you would have to at least make an effort to keep the pedals moving. this may prove annoying, so how about having a "reverse sensor" where if you backpedal (much like some bikes can) instead of the internal brake slowing you down it actuates a switch to flip on the generator. actual braking is done via the grips on the handlebars like normal. |
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The first law of thermodynamics is: you do not talk about thermodynamics. |
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Yes, I think there is merit here. It's essentially a low capacity regenerative brake. It's similar to a Prius hybrid - the human taking the place of the fuel engine. |
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I suggest capacitors or supercaps in place of, or alongside, batteries. |
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Using a single motor/generator is interesting - it may be possible to very rapidly (>100khz) switch between the two polarities, and pulse width modulate the two states against each other. Or do something with the back EMF. Maybe. Here I come up against the limits of my understanding of electromechanics. |
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How's this for a thought - the pedal chain drives the stator and the rotor is attached to the wheel, or vice versa. If the hub is rotating faster than the wheel, it's a motor; if the wheel faster than the hub, it's a brake/generator. |
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Find me the weight and cross sectional area of your regenerative brake system. Determine the total energy required to overcome wind resistance and rolling resistance. Don't forget to add in any losses from the additional gearset. Tell me if this is less than can be recovered and utilized by the regenerative brake. |
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If it is, I will be extremely surprised. |
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Bikes had generators to run lights. |
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