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Old 11-08-2009, 05:23 PM   #1 (permalink)
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Question Brainstorming: Pedal Assisted Electric Scooter

Hi all, I have an idea and could use some feedback/brainstorming from people who know what they are talking about (i.e. not me).

My idea is for an electric in town commuter bike (I have an old 1980 Honda c70 72cc scooter that gets about 70-80mpg and it is the main inspiration for this project). Ideally it would have the form factor of a classy scooter (again the c70 passport being my favorite) and would be powered by an electric motor with a top speed of at least 35-40 mph (45-50 in a perfect world). The range would be 20-30 miles on a single charge, but here's the kicker, it would be pedal assisted. In the first gear the pedals would aid in getting the bike moving, hopefully taking some of the weight off the motor for that first push (and maybe saving a lot of juice?) and then past 1st gear would act as a charger for the battery (like a household exercise bike power generator). To add to the utility it would have a "neutral charging" gear and a very solid kickstand so at long stop lights you could put the stand down and pedal charge the batteries while waiting for the light to change. The idea here is to be able to increase the range of the vehicle as well as increasing the cost effectiveness as you could pedal it in neutral at home before/after rides to reduce the amount of power drawn from your home to charge the batteries.

The problem is I know nothing about mechanical engineering and even less about electricity and batteries. I welcome any and all ideas, critiques, support, etc. Is this possible?

edit: A few extra thoughts I just had: Ben, when you read this, know that I do remember you saying that the Honda c70 frame is fairly impractical for an electric mod, so I'm letting you know I'm not married to that frame

What's most important to me is that it be a viable daily commuter/around town errand machine. With that in mind there has to be some kind of storage solution possible in the future, some kind of container/basket that can be attached for carrying a small amount of groceries and the like.

In a perfect world this bike would be able to travel up to 45 miles an hour, be useable for commuting or light errands on a single charge (I think the 20-30 miles would be sufficient) and with the pedal power added would have increased utility, range, (health benefits ) and heck, maybe via a lighter outlet could be used to charge small electronics in that "neutral charging" gear i mentioned.

I realize this is probably insanely ambitious, but my goal is to save money now, and use the next 2 years (before I move back to california) to brainstorm, plan, and research this project so that when I do settle in back in Cali I can start the project!


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Old 11-08-2009, 08:57 PM   #2 (permalink)
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A mechanically simple way to do it is to add a planetary gearset and another motor/generator to make a CVT. The electronics to control it will be more complex but being able to define the operation in software is worth it.
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Old 11-08-2009, 09:30 PM   #3 (permalink)
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I have some exposure to this as an owner of a Chinese electric bicycle.

To get that speed and range you will need lots of battery capacity- big and heavy and moderately expensive (lead acid), or less big and heavy but even more expensive (li-ion or whatever high-tech); pick your poison. You will be on the upper end for voltage too in order to get your desired speed. Cali is hilly and you will need plenty of gear choices for the pedalling part.

My electric bike looks pretty much like a C70, and it has a great rack! The biggest thing I don't like about my electric bike is that the pedalling part of it seems to be just a legal formality- it can be pedalled but it ain't no fun. I'd say you don't want the ergos set up so that you're sitting on it like a C70- you want it set up like a bicycle first and foremost if you are serious about helping it along via pedalling. Now if that means traditional upright or recumbent or whatever, that is up to you but I know scooter ergos are all wrong for pedalling.

My latest and greatest electric bicycle dream revolves around a full-suspension aluminum mountain bike with an electric hub motor, stout battery pack, and large basket(s)/rack(s). Oh- and fenders too (raining today and I got the ol' stripe ).
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Old 11-08-2009, 10:15 PM   #4 (permalink)
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Aye, mopeds typically have the seat too low for easy pedaling, and the pedals are often set wide on short cranks - they are there for the legalities. A recumbent setup increases safety and reduces wind resistance . However, before learning all the other engineering, look at the basic power numbers. That Honda cub engine is breathing hard most of the time. It is putting out about 50 times as much power as the average cyclist, so adding pedals, even if they are effectively arranged, just gives you an exercycle on a motorcycle. It could be fun various ways, but not a great advance mechanically.
John Tetz has built pedal streamliners with two and three wheels, using a weed-eater motor to assist on hills only. He averages around 30 MPH @ 1,000 MPG. The nice thing about a low-power pedelec is that it can both encourage your own efforts, and even out the output you have to make, and even if the battery dies, you are still mobile.
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Old 11-08-2009, 10:21 PM   #5 (permalink)
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having seen and ridden a number of electric scooters and motorcycles and having built a number of electric bikes, a sloppy electric mini-motorcycle and having worked on alot of gas motorcycles, the C70 is maybe the least practical vehicle to base a project like this off.
I would go for an electirc bike, really, take a look at them, there are some nice ones out there, some nice kits, 40mph is not an issue with the better kits.
If you really want to be able to pedal at stop lights look at a honda gyro, they look weird, but what you are wanting to make is going to look weird either way.
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Old 11-08-2009, 10:37 PM   #6 (permalink)
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Re: pedalling at stop lights: for one thing even though it seems like red lights last forever, you aren't there long enough to really accomplish anything. Plus if you've been helping along the way you will welcome the break from pedalling; and finally, there is the practical matter of putting a centerstand down, pedalling your arse off, then quickly putting it up again on the green. I don't think so.
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Old 11-09-2009, 01:53 PM   #7 (permalink)
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Frank Lee: Do you have a picture of your electric bike, or can you tell us the make/model so I can google it? Also good point about the pedaling at red lights... it would be impractical but...

I don't know the mechanics of it, or how to imagine such a gear setup... but the idea is that the pedal assist is only in first gear to add some extra torque to that first push (or to take some of the heavy lifting off the motor for going up hills, so maybe gears 1 and 2). Then after that the pedal would stop aiding the motor and really only act as a pedal powered charger for the batteries. The other inspiration behind that function is the idea I posted about it having a "neutral" gear specifically to function as a pedal operated power generator (like those exercise bikes you can get plans for online that generate enough power to charge cell phones, run laptops/tv's etc.). The idea was that at home in the garage it could function as a pedal powered generator, and could be taken out as a commuter/errand running bike.

So obviously the scooter frame is a dead end, but I'm concerned that starting with a mountain bike setup will not be big enough to support the batteries, engine, and possible cargo space in the future. So if a mountain bike isn't beefy enough (IMHO) and a scooter is ergonomically insane for this application, what's next?

Edit: Ryland, I took a look at the honda gyro... I think you might be on to something there. Perhaps there would be someway to modify it with a recumbent pedaling setup. I like the idea of a 3 wheeler if only because I've had a few bad experiences riding my scooter in the rain/frost, plus the front and back seem to have pretty generous cargo areas (good for batteries and/or errand related cargo). Here's a pic of the model I'm looking at as I write this:



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Old 11-09-2009, 07:37 PM   #8 (permalink)
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http://ecomodder.com/forum/showthrea...hina-9133.html

We have had NUMEROUS discussions here re: electric/mechanical conversion efficiency relating to hybrids and human powered vehicles. As far as I know there is no pedal-powered generator>controller>electric drive motor combo that is more efficient than a typical derailleur chain drive (typically ranging from 82-98.6% efficient, with I suppose 90+% efficiency most of the time). What does that mean? It means you would be wasting more of your pedalling effort with electric drive vs mechanical. Now if you are into the exercise aspect of it then perhaps it's not an issue. But I, speaking as a lazy man, want the most of my effort going efficiently into propulsion as possible.

Really, I think you may already have your ultimate transportation solution in the C70 just as it is. (They are perfect you know)
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Old 11-09-2009, 08:42 PM   #9 (permalink)
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The eCVT (HSD) design does not convert all input mechanical energy to electricity. Read about the Prius drivetrain to get an understanding of how the design works. It can just as well be applied to a bike. The real beauty of the eCVT is that its "gear ratio" can go to infinity in either direction. That is, it can operate in EV mode with the pedals stationary and allow the pedals to charge the battery with the bike stationary. In normal operation, it can also measure mechanical power very accurately by measuring the currents and frequencies. Therefore, it can measure how much effort was put into riding the bike - which was a frequently asked question with no clear answer.

Another advantage is that it is possible to only extract power during efficient pedal angles. And if it is a bicycle built for two (tandem), the two riders can pedal at different rates if there are two PSDs.
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Old 11-09-2009, 09:07 PM   #10 (permalink)
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Where is this thing?

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