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Homemade electric bicycle

  1. Sep 28, 2016 #1
    I started learning solidworks at my school and got this idea for a folding bicycle as I need one and they're really expensive. I was planning on modeling it after a montague paratrooper bike. Then I thought I could put an electric motor on the rear wheels either by a sprocket or by just putting a metal bar up against the tire that could help spin the wheel (which would be easier but less efficient).

    My question is though does anyone have some ideas on a cheap motor i could get from like a broken appliance. So far my thoughts are a washing machine or electric weed whacker.

    Also what are your thoughts on somehow recharging the battery? I thought about attaching a car alternator to the rear wheel. Although i'm not positive if the wheel would be moving at enough RPM's to get any sort of output to recharge the battery (probably a 12v quad battery).

    Just looking for some thoughts or advice Thanks
     
  2. jcsd
  3. Sep 28, 2016 #2

    GQC

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    hey,

    Cool project!
    I've taken apart a few electric weed whackers (to get the motor out of them) and i can tell you that they wont be strong enough to move a bike.

    I dont know much about a washing machine's motor, but my guess is that it might be too bulky?

    id try using a starter motor. the one on my riding lawnmower launched its self out of the engine one day, so its pretty powerful, and its pretty compact. So i think that would make a good motor to help out with your pedaling. However, Ive heard that they arnt supposed to be run for extened periods of time because they might over heat. So if you do use one make sure its very well ventilated (having air flow inside the motor case will help also).


    If you manage to snag a brush-less DC motor (or most AC motors) you'll be all set for recharging your battery. all you'd have to do is set up a circuit to redirect the electricity generated from the motor its self into that battery, change it from AC to DC (pretty easy with a few diodes) and boom! your recharging on the downhills. An easy way to tell if the motor will work is to check if it has real magnets inside. if it does it should work just fine.

    hope this helps :)

    (oh I just randomly found this cite so not sure if ill answer any questions asked cause i probably wont check this again.....yaa...GOOD LUCK :D )
     
  4. Sep 29, 2016 #3

    NascentOxygen

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    Staff: Mentor

    For the record: you cannot effect the recharge of a battery while simultaneously drawing from it the power to do so. It is not clear whether that may be your plan, or not.

    Forget about having a second device to use as a generator while coasting downhill, this is inefficient and needlessly complicated. When an electric bike goes downhill, the motor gets rotated by the wheels so acts as a generator itself—you don't need a separate generator to reclaim some of the downhill kinetic energy and put it back into the battery. Though you will need a smart controller to oversee all this.
     
  5. Sep 29, 2016 #4

    GQC

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    Ya, i guess I didnt make that very clear, but that's what i meant. The electric motor that powers the bike would charge the battery on the downhills. And depending on how you set the circuitry up you wouldnt need a controller. All you'd need to do is set up a variable resistor switch to control how fast you go, then use a bunch of diodes to control how the electricity flows. So when the controller switch is off the electricity generated from the motor gets converted to DC and charges the battery.
     
  6. Sep 29, 2016 #5

    NascentOxygen

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    Staff: Mentor

    Presumably you'll want to maximize the distance travelled on one recharge, so this means you replace the power-wasting variable resistor arrangement with a power-saving electronic controller, and the rest is as I stated.
     
  7. Sep 29, 2016 #6
    The traditional way of setting up an e-bike is to use a three phase permanent magnet BLDC motor. In that case you use an electronic speed controller (ESC) that controls motor output using PWM. Motors like this are common and you can even make them yourself; http://www.gobrushless.com Though for regenerative braking you need a controller that supports it so that might be a limitation in finding a suitable motor controller.

    Power supply would typically be a bank of ten or more LiFeP04 cells for 32V nominal and higher. These cells are easy to find either in a steel cased round cell or prismatic pouch. They are a bit pricey but they have the best cycle life and highest charge/discharge rates. They're also one of the lighter and more compact types of batteries. The best ones come from A123 Systems; http://www.a123systems.com/
     
  8. Sep 29, 2016 #7

    GQC

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    Right, wasnt thinking about the power loss from the resistor.
     
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