DIY Electric Bike :D:D:D

Discussion in 'Electric Bikes' started by lmlPEZlml, 8 Nov 2011.

  1. lmlPEZlml

    lmlPEZlml New Member

    Hey guys sorry to have made my first post this crazy :biggrin: basically I've been wanting for some time to add some kit to my bike to accelerate it a bit (there's a lot of hills and strong wind in the coastal town I live in)

    I've seen the traditional eBikes and hub motors but since I dont have a grand lying around I've been racking my brains to come up with something I can put together easily.

    One of the things I saw people doing on YouTube is attaching a starter motor to the bike. I work with a mechanic occasionally so I can procure a starter and battery pretty cheap, does anyone have any experience with buildling and/or riding starter bikes? Advantages are I guess that those things can put out a hell of a lot of torque and because of the way theyre made there wouldnt be any need to fit a freewheel. Disadvantages off the top of my head are that the things burn out quite quickly and that I'd have to fit another chain drive (just to be clear I still want to pedal, I'm not looking to replace that part) and the hassle/cost of having a cog machined to fit the starter motor...

    I had another idea too, someone scoffed at this on yahoo answers which is why I thought I'd come and ask some fellow cyclists if its feasable. Basically, my idea is to turn the entire wheel into a motor armature. If I can fit the wheel with some reasonably weighty blocks of iron (or any magnetic metal) then I can attach a strong electromagnet above the wheel and have it pull the block in as it approaches and then disengage to let it pass. Fellow on yahoo told me this was a very ineffective method. I agree that it is in some respects, but the £1700 hub motors he offered as an alternative are a bit less effective for me in terms of price lol! Advantages of this system would be that it would be pretty much silent, very very easy to build and cheap. Disadvantages I can think of would be that it would probably need cleaning and that quite a lot of energy would be wasted in the process (however, using a 90kg pull electromagnet should ensure ample force is generated ;)

    Has anyone here done a DIY motorised bike and do you have any tales and tips to share with me? I'd really live some advice :o)
    Will post videos when my project is finished :biggrin:
  2. middleagecyclist

    middleagecyclist Call me MAC

    Haven't got a clue but going to really enjoy reading the responses to this one.

  3. snailracer

    snailracer Über Member

    Your design does not seem viable because it would be grossly inefficient. For any usable range or torque, I would estimate you would have to carry more batteries that is physically possible on a bike.

    Real motors are constructed with very small clearances (1-2mm) between the rotor and stator, with consistent overlap, and are still only about 50% efficient at best. While maglev trains work on a similar principle to your idea, and have wider clearances, they don't have to carry their own batteries with them.
  4. Friz

    Friz The more you ride, the less your ass will hurt.

  5. Night Train

    Night Train Maker of Things

    Greater Manchester
    A car starter motor is no good for use as a traction motor as it doesn't have free rolling ball bearings but bushes instead. The bushes are not designed for more then a few seconds or running time. Also the motor cannot run continuously for more then a few seconds due to the heat build up in the motor. They are desgned for starting engines not driving vehicles, even bicycles. They are also extremely heavy fo rhte small amount of power you can get out of one.

    If you are in the UK we also have laws that restrict the amount of continuous power you can have on a bicycle before you become a motor vehicle and have to pay road fund licence, have insurance, a helmet and an MOT test as well as conforming to all the otehr regulations around a motor vehicle for safetyand lighting and suspension etc.

    As for turning the wheel into a motor. Either you are a very experienced and knowledgable motor designer, in which case you can afford to buy an ebike kit or you don't realise the complexity of designing a motor. It is a bit more then a few magnets and some wire wrapped around a former. The effort and expense of getting it right would be considerably more then just getting a kit. You 90kg pull electro magnet, working at the distance needed to affect lumps of iron on the wheel, would be about the size of one of those used on the scrap metal yard crane and use more power then your house.

    The only sucessful person I know of to do that is Cedric Lynch and he went on to create the Lynch motor and then moved on to the Agni motor.

    Your system would have a power to weight ratio so appalingly bad that it would be easier to not have it and just carry the bike in a box over the steepest hill! Not really surprised it was scoffed at as it is about as bad an idea as putting a couple of Pacific steam locomotives onto the wings of a light plane with propellors attached to the loco's wheels! No amount of shovelling coal will make the plane move never mind take off!

    You would be better placed to have a look on ebay for a small second hand dc motor for a bike. I picked one up for about £20. Then you will need a controller, a throttle pot, light weight lithium batteries, a charger, a load of cables and waterproof connectors.

    Actually it would still be cheaper to just buy a kit!
  6. fossyant

    fossyant Ride It Like You Stole It!

    South Manchester
    Legs :biggrin:

    Training man, it's the only answer. Electric assist :wacko: time to get fit !

    Wrong forum.... :whistle: was it wheelchair chat you need :biggrin:
  7. fossyant

    fossyant Ride It Like You Stole It!

    South Manchester
    Oh and as the electric assist bikes are power limited, you'll get more watts out of your two legs as well :thumbsup:
  8. Dan_h

    Dan_h Well-Known Member

    Reading, UK
    I think this is on the right lines. Fit some weighty blocks of iron to the wheels then take it and ride it up hills every day for a month. Then take the blocks of iron off and presto, no more need for an electric motor!
  9. mark c

    mark c Über Member

    Forget batteries to heavy and limited range , go the hole hog Go Pulse jet no moving parts easy maintenance fuel from any diy store and 80 mph.:thumbsup:
  10. middleagecyclist

    middleagecyclist Call me MAC

    I knew this was going to be good!
  11. OP

    lmlPEZlml New Member

    Thanks everyone, noted! I don't think you're giving starter motors enough credit here, theyre really really not that heavy (I work with them all the time) neither are the batteries really, and yeah I realise they burn out after ten minutes but I was mainly going to use electric assists for getting up to speed quickly then legs take over from there! I'm not looking for it to take me around the country lanes and stuff just as a short sharp boost when I need it. I've seen a chap online attach a starter motor to his BMX and do 45mph. Lots of other people have used them with sucess (until they burn out after 20-30 mintues of continuious use) but I wanted to avoid it if possible cause it'll be an arse to implement, I'd have to have cogs machined and stuff and I'm way to poor for that :sad: (hence looking for a DIY solution rather than just going out and buying an expensive kit... I have been looking at them but decided to stop torturing myself lol)

    You guys sure have put me off the electromagnet idea :sad: However, the 90kg ones I was looking at are 8cm in diameter (so not as big as the scrapyard ones) and can easily be powered by a car battery. I thought you could put the electromagnet parallel to the wheel to allow for tiny clearance as that obviously would be more efficient. Perhaps you could even use permenant magnets on the wheel and have a system of repulsion rather than attraction like I described in the first post. Would this really be completely ineffective? Car batteries really really dont weight that much, i could comfortably ride around with at least one on there, hell I sometimes carry more weight than that anyway! And I don't mind if they drain fast I've got a charger!! I understand it could go terribly wrong but surely theres an optimal way to set it up? Any ideas? I can't quite believe that a system like that with 90kg lift magnet could be ineffective, theyre tiny and the like I said the weight of a 12v car battery is not an issue. (Please feel free to debunk that in a mocking way)

    Oh and thanks fossyant I loled... I get around alright would just be nice to have something a bit more punchy. I'm a fairly strong cyclist after some 20 years of riding literally everywhere, but if I can make it go faster, well.... it has to be done really xD

    mark c, have you seen the geezer on youtube that attached a rocket engine to his bike? jesus christ!!! they recon he did 150 down this airstrip lol, i bet he needed to change his shorts and the saddle after that... will post the video if youre interested, its pretty funny

    cheers guys please keep the ideas and criticism coming
  12. Friz

    Friz The more you ride, the less your ass will hurt.


    Oh I like your style.
  13. Dan B

    Dan B Disengaged member

    A 26Ah SLA golf cart battery weighs around 7kg. (I expect an ordinary car better is about the same pound per amphour, but you don't want to use one of those as it's not designed for deep discharge). If that's really not a noticeable extra weight to be riding around with, I reckon you're a strong enough cyclist not to need the assist.

    Of course, if you're just doing it for shoots and giggles then more power to your elbow and I look forward to seeing the youtube videos. But as a practical transport solution, I don't see it really
  14. OP

    lmlPEZlml New Member

    search "rocket bike" on youtube for hilarity ;)
  15. rowan 46

    rowan 46 Senior Member

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