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Motors E-Bicycle build

Discussion in 'General' started by xen0morph, 26 Apr 2007.

  1. xen0morph

    xen0morph Bargain wine connoisseur

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    I'm looking into turning my push-bike into an electric bike for the summer (no helmet, tax, MOT, or insurance required as long as I keep the pedals working too). I've found a source for the motors (300 watt Scooter motor) and batteries but I'm having a bit of a problem working out how to mount the motor so it can use all 7 of the gears on the back wheel, whilst still keeping the pedals freewheeling. Could anyone give me some suggestions?
     
  2. GreatOldOne

    GreatOldOne Wannabe Martian

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    I'd assume that you'd have to mount the motor either in front of, below or above the main sprocket pedals, and then extend the chaint to encompase the main sprocket and whatever sprocket you fit to the motor....

    Arrgh - no, you can't do that - the peddles would still rotate with the motor, as the chain is still moving.

    That's the problem, isn't it - to use the gears, you need the chain to move.

    You could always just do the typical thing of using an idler wheel on the motor, and pressing it against either the front or back wheel - you'd loose your gears, but you could control the speed via some sort of pot, couldn't you?
     
  3. xen0morph

    xen0morph Bargain wine connoisseur

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    The motor is 300 watts at a maximum speed of 2800rpm. I want a top speed of something approaching 25mph at full power (although the legal limited speed is 15mph, technically). If I go for a single-speed reduction drive do you think there will be enough torque to go up hills etc effectively?
     
  4. vetlel

    vetlel New Member

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    Just a quick thought:
    Can't you do something like this? Solex

    And a possible addition to this could be a cone shaped wheel on the motor ( variomatic style), the different circumference of the wheel would give you some kind of gearing...

    This way the electric part is completely seperate from the original bike, and you could even help the motor a bit, by pedaling, to tackle the hilly bits...

    Edit:
    I remember something about bikes with the electric motor in the hub of a wheel...

    Edit2:

    here you go

    (in dutch, but the brand names should help you on your way.)
     
    Last edited: 26 Apr 2007
  5. GreatOldOne

    GreatOldOne Wannabe Martian

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    That's pretty much what I had in mind when I suggested using friction drive on the tyre with the motor - it's what the solex does, but with a small IC engine.

    Which, according to the website is has a power output of 0.58 KW (almost twice the motor you have). A 300w motor should prob. work, but not very fast, I guess... But It'll have a shed load more torque than a little 49cc engine.

    I think it's time for some experiments! :)
     
  6. BjD

    BjD New Member

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    Hmmm, you could go the route I've seen many bikes of having the motor driving the rear tyre directly. Assuming a bike wheel of 26inch outer diameter, to hit 25mph at a motor speed of 2800rpm requires a 8.5 times reduction, which means a driving wheel on the motor of 77mm, which seems reasonable. Theres some rounding in those calcs and thats based on 26inch rims, not including tyres :) I don't really know common bike wheel sizes.

    Problem with that is its a lossy transfer of drive between the motor and wheel as you're relying on friction. It'll probably slip when its wet.

    You'd need the torque output of the motor to know if an 8.5 reduction is enough. Then do some calcs based on the overall mass of you+bike and the grade of the steepest hill you plan on going up to see if its enough to be useful.
     
  7. GreatOldOne

    GreatOldOne Wannabe Martian

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    Just followed a link on that Solex site for electric bikes, and they claim that:

    according to Google, 300 watts is just over 0.4 Horsepower - so if that claim is correct, your motor will have the equivilant torque of a 1.2 hp IC engine.

    The 49cc engine on the solex pushes out 580 watts, which is 0.78 Hp - which means you'd have more torque than the solex.

    I think you'd be OK.

    I ran across this as well - looks as if it has some interesting info in it.

    http://buggies.builtforfun.co.uk/Drawings/Tech-Art-1-7-1-06.pdf
     
  8. Malvolio

    Malvolio .

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    Get a disk-compatable rear hub, making sure that the hoop has breaking flats as well. Then simply get a cog, do some welding/cutting/drilling, and bolt it up to the disk mount. Run a chain (I would think that a 32-14T reduction from the motor-to-wheel would be good).

    The only downside is that you would need an auto clutch that would disconnect when the motor is not running, otherwise you'd have a bit of resistance once you got pedaling again.

    Another option is to look into a Nexus hub my Shimano. They do an electric power-assist hub that works a treat.
     
  9. xen0morph

    xen0morph Bargain wine connoisseur

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    Having the rear hub being driven through the existing chain would be easiest to implement - would I get any advantage from doing it this way or would there in fact be a disadvantage? As long as I calculated the gears etc correctly?
     
  10. Malvolio

    Malvolio .

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    The real problem comes in when you try to drive your rear cassette: it will feel a lot like a "fixxie" (aka a fixed gear hub). When the motor is on, you will have to also pedal, thus defeating your freewheel. Plus you would "lose" one of your gears from your main chainline while pedaling. And again, you would need to have an auto clutch to disengage the motor drive so that you do not have the resistance from the motor while pedaling unassisted.
     
  11. Xen0phobiak

    Xen0phobiak SMEGHEADS!

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    How about using the rear wheel of a pushbike (for the gear hub with the one way clutch/ratchet) at the front of the bike, with the gearing&tensioning system attached to the bottom of one of the forks, with the motor higher up. That way you get to keep using gears and you overcome the freewheeling problem with very little manufacturing needed. (but you do need another bike to use as a donor for the parts)
     
  12. Cookie Monster

    Cookie Monster Well-Known Member

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    Why not just pay the £600 for a Giant Suede. :p ive sold a few in my bike shop. its front wheel driven and has 2 volt settings, normal gets you about 15 miles of travel @15mph hit economy and you get 23 miles @ 11mph (i know the speeds are correct but i may be out a little on the milage)
     
  13. Altron

    Altron Well-Known Member

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    The problem with mounting it on the front wheel is that it will make steering more difficult. It's no biggie in a car where you have power steering, or at least some sort of gear reduction, but in a bike, where it's directly attached, and where it's designed with a relatively light fork and wheel in mind, adding significant weight would significantly increase the grip on the front tire, which would make it harder to turn.

    What I would do is take a look at the way the rear cassette attaches to the rear wheel. See if it would be possible to attach a second cassette to the left side. Best place for the motor would probably be a "rat trap" (the small tray-esque things that you can get that sit above the rear wheel and hold stuff), with a chain running down the left side to the left cassette. Then on the right side, keep the existing drivetrain intact.

    I think it would be advisable, however, to attempt to use large gears on the left cassette. It would still need to freewheel, but for something like an 8.5:1 ratio, you'd need a tiny 1" gear (think the size of gears on the rear derailleur) on the motor, and a big 8.5" gear (think the size of a large road bike second or third front gear).

    Otherwise, you could also try a two chain thing, but that might be more complicated. Something like a 1" sprocket on the motor, going to a 3" sprocket, attached to a 1" sprocket, chained to a 3" regular rear wheel sprocket. You'd have to be really careful about aligning it all.

    One thing that may be applicable, however, is the fact that an electric motor is very similar in construction to an electric generator (the motor converts charges moving through an area with magnetic flux into an angular force, the generator uses torque to move an area with magnetic flux which creates moving chargers), and with some clever design, you might possibly be able to have a setup where pedaling recharges the battery.
     
  14. thestig198

    thestig198 Artificially Intelligent

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    I don't think you'd be able to put a rear wheel on the front because rear hubs are wider and it wouldn't fit between the forks.

    I have seen trials bikes with the freewheel at the pedals, so the chain goes round when not pedalling. Doing something like that would allow you to drive the motor directly onto the rear hub. Problem is I imagine these front freewheels are rather expensive and the front chain ring on trials bikes is usually very small.
     
  15. Xen0phobiak

    Xen0phobiak SMEGHEADS!

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    Easily fixed with a welder if its a steel bike.
     
  16. vetlel

    vetlel New Member

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    Hi, came around this through hackaday. He's got one wheel to many, but there just might be some interesting bits on there for you...
     
  17. Fusen

    Fusen New Member

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    gah, when will an electric bike come out that doesn't look like the current electric bikes :p

    I want just a normal looking mountain bike that is also electrically powered, obviously you have the problem of where to hide the motor and batteries etc but tbh, until this design issue is overcome I really don't think e-bikes will take off with general consumers.

    The current crop including the Giant Suede just look too much like old fashioned womens bikes :/
     
  18. vetlel

    vetlel New Member

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    I used to dabble in design a long time ago. (study and a half hearted attempt to make a living out of it.) The trick is to not hide things you can't: just incorporate
    the electrical bits in the design. If you can't beat them, join them.
     
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