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  1. #1
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    Interested in Building an E-Bike?

    Hello Everyone,

    I recently got a new toy, a Raptor 4.0 electric skateboard made by the Exkate folks in California. Let me tell you this is ~by far~ the best 'toy' I've bought for myself, and believe me, I've bought many toys over the years ;-)

    Anyway, the reason this is relevant is because I've found this skateboard, powered by a 450W 24V motor, is able to climb some serious (bicycle => granny-gear) grades and has incredible range (I cruised for over an hour by the waterfront in downtown Portland last weekend with juice to spare)!

    Experiencing this two facets (speed & range) of electric propulsion first hand has inspired me to want to extend my electric experience to my commute (~13mi, some hills), especially with summer now here and gas approaching $3.50. I figure that if the single-speed electric skateboard, with its single-speed drivetrain and tiny soft wheels, and an upright rider, can already do so much, then a well-designed electric road bike may actually be a viable transportation vehicle!

    My primary design goal is to attain a 'safe' average speed of 20mph, with a useable range of 15mi (I can recharge at work for the return trip). I'm not a super athlete, but I reckon I should be able to put out 150-200W without breaking a sweat (which is a design goal for a commuting bike). To take a bike up a 6% slope at 10mph takes 300W so assuming a continous-duty derating factor of 0.8, a motor mechanical-efficiency factor of 0.6, I figure I'll need a motor of about (300-150)/(0.8*0.6) = 312W rating. At 36V, this would imply a peak current of 8.7A. http://www.electricscooterparts.com/motors.html has a very well built surplus 300W Kollmorgan (not the cheapo Chinese motors like those on my skateboard) for $40, which for me, is what inspired this whole train of thought!

    Assuming a desired average combined output of 300W, I put in 150W, and the bike puts in 150W, and assuming a motor-controller efficiency of 0.9, a battery conversion efficiency (high-current derating factor) of 0.8, a discharge factor of 80%, for trip duration of 40mins, I figure I need a battery of (0.7*150)/(0.9*0.8*0.8) = 182Whr.

    The batteries I have in mind are the new Dewalt 36V lithium nano-phospate packs that uses the bleeding-edge crem-de-la-creme cells made by A123 Systems. They are 2.4AH, I believe, or 86Whr. These go for ~$110 on Ebay these days, so I can only afford two, for 164Whr, which is shy of the 182Whr above calculated :-( Oh well, I guess I have to get off my lazy butt and up my leg share to 55% (165W).

    Which brings me to why I'm posting this -- the drivetrain. This is no doubt the most challenging, costly, labor-intersive part of this whole project to build a custom e-bike. I would like to find a partner (or two) who is interested in building such a bike in the hopes that together we can drive cost, effort and risk down while banging our collective heads together and (hopefully) having fun as well.

    My philosophy is to KISS as much as possible. I view the two foremost goals of the e-bike are to make hill-climbing a non-gasping/sweaty affair and upping average travelling speed -- all other considerations can be sacrificed. My current idea for the drivetrain is a very simple one, but one that I think can be made cheaply, is highly efficient, robust and lightweight. The only caveat (heh heh) -- clipless pedals are required to ride this bike (which should not be a problem for most experienced bicyclists).

    I have a Trek aluminum (all round tubes) road-bike for this project. I'm thinking of taking a bicycle chain sprocket and attaching that to a jackshaft (i.e. an intermediate shaft). This shaft gets attaches to the bottom of the upwards-sloping bottom tube of the bike. A chain links the innermost (smallest) chainring on the pedal cranks to this sprocket. On the other side of the jackshaft is a large pulley, and the motor is mounted as low as possible on the inside V of the frame and drives the pulley via a timing belt and a small pulley. That's it! If you've followed me this far, you'll ask -- where's the freewheel? Er hmmm -- remember the clipless pedals requirement ... ?! Don't worry, to prevent embarrassing bloody shins when you walk in the office in that all-revealing lycra, a safety motor cutoff switch will get installed on the brake lever -- pull the brakes and the motor-controller shuts off immediately. A resume-button will resume the previously set throttle-level. Seems vaguely familiar? Well, you heard it here first -- the world's first cruise-control bicycle!

    So if you're read this far, you must be interested, or critical -- in any case please reply and let me know :-)

  2. #2
    Scott n4zou's Avatar
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    The easiest way to convert your bike to electric is to install a hub motor kit. Just go to this link.
    http://www.werelectrified.com/unibikekit.html

    A better choice may be to order a complete electric bicycle. Wal-mart has a super deal on an electric bicycle. It has the same 450-watt motor as your skateboard on a bicycle designed to have electric power. Best of all this electric bike only costs $279.46!
    http://www.walmart.com/catalog/produ...uct_id=5391437

  3. #3
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    Quote Originally Posted by n4zou
    The easiest way to convert your bike to electric is to install a hub motor kit. Just go to this link.
    A better choice may be to order a complete electric bicycle. Wal-mart has a super deal on an electric bicycle. It has the same 450-watt motor as your skateboard on a bicycle designed to have electric power. Best of all this electric bike only costs $279.46!
    Hi,

    Thanks for the heads-up on the Wal-Mart deal -- unfortunately, although I have no qualms with the price, I do like the feel and look of my roadster . Also, a 90lbs bike (like that) would be quite a monster to have to wrestle with when an electrical breakdown happens, not to mention hefting it on my bike rack for weekend trips.

    WRT the hub kit, with exception of the Bion-X, hub motors have terrible efficiency and low-torque (for the same wattage as other types of drivetrains) because of the low-rpm. Geared hub motors aren't cheap, and also they don't work on 700c road bikes. Besides, at 6ft tall -- not exactly a good candidate for a one-size fits all bike.

    For a nerd like myself, building the bike is very much part of the e-bike experience ...

    An update on my previous posting:

    I got a chance to try out the Dewalt/A123 lithium nanophosphate battery pack this weekend. Of course, since my bike is not built yet, I could only try it (ducked taped!) on my electric skateboard. Absolutely fantastic performance! The motor-controller on the Raptor didn't mind the 36V and the 24V motor survived the occasional full-throttle. The acceleration I feel when I pull on the trigger is better than my 240HP V-6 SUV :-)

    The downside was I was caught off-guard by the much-shortened range of this 83WH (I think I got abt 15mins of heavy-trottle fun) vs the original 384WH -- I had to hoof-it back home. True to its reputation, these A123 cells have an extremely flat-discharge curve until the very end, and then they fall over in a blink of an eye. I'm going to revise the bike design to accommodate 3 of these packs. As each pack weighs the equivalent of two soda cans, it doesn't affect the feel of bike at all ... although it might hurt the wallet

  4. #4
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    You're gonna need a freewheel crank. I wouldn't like the idea of a motor pedalling my feet if I don't pedal. That would also be a waste of energy. Your motor sounds similar to the kit at http://www.cyclone-usa.com.

    Ideally, someone out there can build a bicycle frame with a large bottom bracket that is designed to accomodate a motor with a free wheel crank and a torque sensor. The motor would be neatly housed inside the bottom bracket and you wouldn't need extra chains and brackets. The wires would run along the insides of the frame and you'd have power jacks at the front and rear for batteries and/or lights. With an aluminum frame that accomodates 700c tires, and lithium ion batteries, the bike could weigh less than 35lbs. And if you can add road slick tires, you can get incredible range and speed.

  5. #5
    Senior Member wubrew's Avatar
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    Quote Originally Posted by adamtki
    You're gonna need a freewheel crank. I wouldn't like the idea of a motor pedalling my feet if I don't pedal. That would also be a waste of energy. Your motor sounds similar to the kit at http://www.cyclone-usa.com.

    Ideally, someone out there can build a bicycle frame with a large bottom bracket that is designed to accomodate a motor with a free wheel crank and a torque sensor. The motor would be neatly housed inside the bottom bracket and you wouldn't need extra chains and brackets. The wires would run along the insides of the frame and you'd have power jacks at the front and rear for batteries and/or lights. With an aluminum frame that accomodates 700c tires, and lithium ion batteries, the bike could weigh less than 35lbs. And if you can add road slick tires, you can get incredible range and speed.
    adamtki,

    what's your opinion on cyclone motor? Thinking about fitting it on a 20" folding bike.

  6. #6
    Scott n4zou's Avatar
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    Have you thought about using your skateboard with the bike? I was given an old electric scooter, which was not street legal. I striped and modified it so I could bolt it to a TRI Hitchhiker, a one-wheel trailer that originally was used for hauling a child behind the bike. I removed the seat and pedals and bolted the modified scooter frame to the dropouts and chain stays of the trailer. I extended the throttle cable so it could be placed on the handlebar, of course! I've ridden this rig and it's quite fun and safe. Below are photos of the end result.



  7. #7
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    Quote Originally Posted by wubrew
    adamtki,

    what's your opinion on cyclone motor? Thinking about fitting it on a 20" folding bike.
    Have never used it. It's a great concept - you use your own wheels and you're using the motor at peak efficiency all the time. It comes down to that whining noise. I have yet to hear it, but if it's too loud, I would be reluctant to get it. But that's just a personal matter.

    I have heard that the freewheel crank is somewhat on the cheap side and may break if you put too much strain on it. But perhaps that was just a bad batch.
    Last edited by adamtki; 05-23-07 at 04:23 PM.

  8. #8
    Senior Member acroy's Avatar
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    Best part of the Exkate is the hottie in the pictures
    http://www.exkatemania.com/electric_...ard_videos.htm
    beer-bottle target

  9. #9
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  10. #10
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    Hi. I'm new in diy Ebike. I'm planning to build an electric mountain bike. Can somebody tell me how much power does a motor needed to propel the bicycle without pedalling?

  11. #11
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    If you aren't going to pedal it, it is an electric motorcycle, not a mountain bike.

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    Smile Re

    Yeah, you are right. I just want to make my long journey more easier, sometimes pedal, sometimes not. But if I'm building an electric motorcycle, I need license. Moreover, electric motorcycle is dangerous(speed).

  13. #13
    put our Heads Together cerewa's Avatar
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    If you aren't going to pedal it, it is an electric motorcycle, not a mountain bike.
    EDIT : what you see above is a quote from crackerdog, post#11. Below is my response:

    Most places require an electric-assist bicycle to have working pedals, but don't require you to use them.
    Last edited by cerewa; 10-29-08 at 07:40 AM.
    Some awesome folks who are working to give Haitians the ability to manage their safety and their lives:
    Haiti Partners

  14. #14
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    I am confused, I don't pedal my bike sometimes, so sometimes it is an electric motorcycle?
    cerewa:
    If you aren't going to pedal it, it is an electric motorcycle, not a mountain bike.? I think theres more criteria than that for most places.

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