Bottom crank jack shaft.

Discussion in 'Motorized Bicycle General Discussion' started by ferball, Apr 4, 2011.

  1. ferball

    ferball New Member

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    I am making a recumbent, so the I have the engine mounted forward of the my rear bottom crank. (I left it intact on the donor bike for the rear half of the build). So I am able to use the crank as a jackshaft. Here is how I am doing it:

    1. From a donor single crank remove the chain ring and weld the key way spacer from the left side into the cent of the chain ring. On single cranks the left side thread is smaller than the right side thread. The by welding the key way spacer into the chain ring it gives it the right diameter and spins the shaft via the key way.

    2. I chopped off the pedal arm so I had a straight shaft. I had to weld the right side sprocket to the shaft, because the peddle arm is what used to spin the sprocket.

    3. I installed the sprocket from step one on the left side, just pulled off the big nut and put it on and put the nut back on.

    4. I discovered that the crank covers from a three piece crank that I had lying around was the same thread as a shimano free wheel, so I welded the crank cover with threads facing out to the right side of my shaft so I my pedal chain will now hook directly to the jack shaft on a free wheel.


    I will post some pics, but it is a cheap easy why to do a jack shaft. It is also super easy to change the left side gear, so I could make different sized sprockets to change gearing ratios.
     
  2. hankmanpei

    hankmanpei New Member

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    Nice plan and I like it, do you have a formula for gear ratio's? what I'm trying to figure out is coming off the motor on the left is a 2" pully inline to a 6 1/2" pully on the j shaft, to the right of the 6" is ???? inline to a 20 tooth sprocket fixed to a 9 speed internal geared hub (SRAM I Motion) to the right of ????? tooth sprocket is a rear BMX freewheel inline with my pedal sprocket, I only have one sealed crank set ( my j shaft) and plan on welding the pully and sprockets on this piece so it's pretty much a one shot deal,
    my previous set-up was the two" pully weldwed to the motor crank shaft, to the 6 1/2
    pully welded straigt to the steel rear wheel hub, this worked great with top speeds of 45-50 mph, and a perfectly smooth running crusing speed 35-40 mph without the motor screaming but a little slugish taking off (this is why I purchessed the 9 speed hub,
    if I used a 20 tooth sprocket inline to the 20 tooth hub would this keep my previous 3:1 ratio and torque the same, or should I change this sprocket to a 14 tooth??? bigger or smaller, j shafts convert horse power to torque t? or f? I really am lst in this area hankmanpei( bodyman/painter extordanaire)
     
  3. ferball

    ferball New Member

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  4. hankmanpei

    hankmanpei New Member

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    Thanks for the Ratio link it's just what I was looking for,Looking at those pics (of your bike) you posted, I'm thinking with a reach like that you must play one heck of a basketball game.lol hankmanpei (bodyman/painter extrodanaire)
     
  5. rich4240

    rich4240 New Member

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    i know i know old thread but i have one simple question i have a 66/80cc china girl and want to bilud a shift kit i know how to do it i have pretty much unlimited axcess to old bmx rims with free wheels how has yours held up

    a reply would be great thanks richard

    brnot
    dnut
    .weld
     
  6. young grease monkey

    young grease monkey New Member

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    Bbs aren't made for high rpm, so if you want it to last then you will need sealed ball bearings. You will need to ream out the threads in the bottomed bracket to install bearings, not too hard.
     
  7. rich4240

    rich4240 New Member

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    Hi I have aredy done that the question is will the BMX free wheel like the small one in his pic hold up to the motor I'm worryed it might just brake ok sbp has a good one but it 70$
    brnot
     
  8. young grease monkey

    young grease monkey New Member

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    Unless you have a pull start, you will need to lock up the freewheel. This can be done by taking off the seal/shield and filling it with solder. If you need a freewheel, I think a bmx one would hold up ok. Try to find a good one, look up the models you have and find out which is strongest. They can handle quite a bit of torque. Oh, and hankman, HP is torque times rpm. Torque is converted to rpm and vice versa. HP is what really matters, torque means nothing without rpm.
     
  9. rich4240

    rich4240 New Member

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    I'm setting it up like the sbp shifter kit but a cople different thing I nead the free wheel so I can run the motor with out the cranks moving ie freewheel but make it so I can peddle to start the motor by the clogs on the freewheel opening and being able to peddle ilits the same way your MTB back rim works
     
  10. Ibedayank

    Ibedayank New Member

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    I think you need to do your research on how a SBP shift kit works.
    If what you say was true you could not pedal start a shiftkit bicycle at all anymore but yet everyone that has one that has unmodified freewheels can.
    The ONLY freewheel that is suggested to make Fixed is the one that comes in a 4G belt trans as it is crap and blows up.

    Oh and torque means EVERYTHING big rigs have a rpm redline of 2200 rpm

    Mechanical horsepower

    Assuming the third CGPM (1901, CR 70) definition of standard gravity, gn=9.80665 m/s2, is used to define the pound-force as well as the kilogram force, and the international avoirdupois pound (1959), one mechanical horsepower is:

    1 hp ≡ 33,000 ft·lbf/min by definition
    = 550 ft·lbf/s since 1 min = 60 s
    = 550×0.3048×0.45359237 m·kgf/s since 1 ft = 0.3048 m and
    = 76.0402249068 kgf·m/s 1 lb = 0.45359237 kg
    = 76.0402249068×9.80665 kg·m2/s3 g = 9.80665 m/s2
    = 745.69987158227022 W since 1 W ≡ 1 J/s = 1 N·m/s = 1 (kg·m/s2)·(m/s)

    Or given that 1 hp = 550 ft·lbf/s, 1 ft = 0.3048 m, 1 lbf ≈ 4.448 N, 1 J = 1 N·m, 1 W = 1 J/s: 1 hp = 746 W





    Torque.

    A force applied at a right angle to a lever multiplied by its distance from the lever's fulcrum (the length of the lever arm) is its torque. A force of three newtons applied two metres from the fulcrum, for example, exerts the same torque as a force of one newton applied six metres from the fulcrum. The direction of the torque can be determined by using the right hand grip rule: if the fingers of the right hand curl in the direction of rotation and the thumb points along the axis of rotation, then the thumb also points in the direction of the torque.[6]
     
  11. rich4240

    rich4240 New Member

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    Ibedayank do you think my BMX freewheel will hold up to the tork
     
  12. Ibedayank

    Ibedayank New Member

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    Rich..

    you can just order just the needed parts to make the freewheeling crank from SBP but you will have to take into account the extra sprocket to run up to the front crank.
     
  13. Ibedayank

    Ibedayank New Member

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    Rich what motor do you plan on using?
     
  14. rich4240

    rich4240 New Member

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    Hi see the thing is I can get every part for free and have lots of skills and no money or I would buy the parts I have a 66/80cc zoom bike motor
     
  15. rich4240

    rich4240 New Member

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    I'll do a quick sketch on ether auto cad or something to show you how I want to seet it up
     
  16. Ibedayank

    Ibedayank New Member

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    With a 66cc 2stroke a good quality bmx freewheel will hold up
     
  17. rich4240

    rich4240 New Member

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    I want to have a Cain from rear sprocket set to the mid triangle ish and weld a baring set to put a set of two sprocket one gose to the rear weel one to the jack shaft at the seet post mid way up then I want to put the free wheel on the set of two sprockets and run a Cain from the freewheel to the crank

    Which in thretory should let me peddle the bike or run the motor with out peddling right?
     
  18. rich4240

    rich4240 New Member

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    Which in theory the only load the free wheel would have is when I'm peddling
     
  19. Ibedayank

    Ibedayank New Member

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    http://www.sickbikeparts.com/Manuals/SBP2 Manual001 Rev A.pdf

    being that the only time the freewheel locks up is when you pedal putting a gear on the left side of the crank on the rear and running it up to the front crank with the gear on that crank reversed so its also on the left side will be the cheapest and easiest way. the the way some tandems have their chains run
     
    #19 Ibedayank, Jul 14, 2012
    Last edited: Jul 14, 2012
  20. rich4240

    rich4240 New Member

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    The middle sprocket would have 2 solid sprockets on to jack shaft one to rear weel then I would weld the bolt that the freewheel bolts on to id wells the bolt to the out side sprocket then bolt on freewheel and run a chain from it to my crank gear
     

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