Simple Electric bike idea?

Discussion in 'General Questions' started by boyntonstu, Jan 27, 2015.

  1. boyntonstu

    boyntonstu Member

    Add a motor and sprocket into the pedaling chain loop.

    Extend the chain to fit half way around the motor sprocket and you would have a motorized bicycle with gears.

    With the power off, you would have to pedal both the motor and the rear wheel.

    Would that be too hard?

  2. KCvale

    KCvale Motorized Bicycle Vendor

    Yes, that would work if you did the chain sort of serpentine to catch enough sprocket teeth and it was a single sprocket back wheel, except for that pesky part about your legs being beat to death by the pedals when using the electric.

    The solution is a new bottom bracket with freewheel pedals and 2 chain rings, one to your back wheel, the other from the motor with the proper gear reduction between each sprocket size.





    And no you don't need to pedal the motor, just use a freewheel sprocket on it and the motor is virtually drag free.

    The daunting part is getting the motor mounted well and dealing with all the wires.
    And don't forget battery cost, those ~1KW triangle LI packs with chargers are >$1K delivered to the US.
    The round 'water bottle' ones can be had for less than half that but be enough for some pedal assist, jut not enough to ride around town for a couple hours wide open with no pedal help.

    Hope that helps.
  3. boyntonstu

    boyntonstu Member

    Wow! You do great work.

    Lets think about it this way:

    The goal is to ride the bike 15 MPH.

    Assume the pedal cadence is 60 RPM.

    I am pedaling with the motor off.

    I press the throttle to achieve 60 RPM with very little leg power.

    As I come to a stop, I release the spring loaded throttle and coast without pedaling.

    Would this scenario avoid legs being beat to death by the pedals?
  4. KCvale

    KCvale Motorized Bicycle Vendor

    Thanks ;-}
    If the motor is running the pedals will be turning with it without freewheel pedals arms.

    Coasting is fine with motor off, but if the motor is moving your pedals will be moving otherwise.
  5. boyntonstu

    boyntonstu Member

    Exactly! One idea that comes to mind is a pressure switch on the pedal. If the pedal wants to go faster than your feet it will pull away, release the pressure switch, and cut the motor off. Not easy, but doable.

    I would place the motor such that it pulls the pedal sprocket from underneath, not pulling the rear sprocket.

    I don't know the required sprocket ratio between the motor and the main sprocket.

    One could choose a lower rear sprocket as the fixed gear to obtain the correct ratio.

    When people say that it can't be done, I show them my $100 Elevator.

    Last edited by a moderator: Dec 15, 2015
  6. KCvale

    KCvale Motorized Bicycle Vendor

    Or you could just let off the throttle when you don't want the motor spinning your pedals :rolleyes7:

    Above, below, in front, behind, it don't matter, it has to reach the back wheel.
    The easy way is just mount a sprocket on the left side of your wheel and run the electric to that.

    If you want to use your pedal side chain so you have gears that's another thing.

    If the pedal sprocket is turning your crank arms then the back wheel sprocket is turning unless the pedal cranks are isolated from the dual sprocket pedal/motor sprockets like a socket wrench.

    I know this is a hard concept to follow for most because a pedal sprocket is always directly connected to the right crank arm or crank shaft, that's why back wheel hubs have built in freewheels, so you can coast.

    The same principle applies to a freewheel bearing the 2 sprockets attach to but allow the pedal cranks to freewheel so like when your back is turning you don't have to pedal along, when the motor is turning the pedal sprockets the crank shaft crank arms freewheel.

    This the budget $20 freewheel bearing that will take 2 sprockets and isolate the crank arms and shaft from any driving force from the second sprocket.


    That will hold up for lower power electrics and stock 48cc gas but that's about it, the better ones that will take most anything are ~$80.

    This is the pedal crank arms, the right screws into the freewheel bearing to attach it to the pedal crank shaft.


    Ya falla?
    (sorry, watched 'The Sting' recently and I love that term)
    boyntonstu likes this.
  7. boyntonstu

    boyntonstu Member


    Great advice and information. (as expected)

    Me 2

    Another concept: The rear has 5 or 6 sprockets.

    Connect pedal chain to 1 sprocket, motor to another.

    Perhaps there would be a good combination.

    My guess is that the motor powers the biggest sprocket.

    2 chains are heavier than a single extended chain, but it may be a good idea for obtaining the correct ratios.
  8. wheelbender6

    wheelbender6 Well-Known Member

  9. boyntonstu

    boyntonstu Member

    That is almost perfect!

    Exactly what we were discussing.

    (I can visualize a chain guard.)

    The next task is to build an inexpensive LiPo battery

    A buddy of mine has been salvaging old laptop batteries with surprising results.

    Not thousand dollar batteries, under 100 bucks!

    I might spring for this Cyclone if I don't do it with salvaged motors.

    These are the specs:

    360 Watt Motor with 9.55:1 Planetary Gearbox and Internal Controller

    Size: Length: 6.183"L x 3.50"H x 3.50"W
    Weight: 6.45 lbs (2.92 Kgr)
    Gearbox: Integral, Planetary - 9.55:1 Ratio
    Rotation: CW
    Sprocket: Not Included
    Motor Controller: Internal, PWM 40Amp Max.
    Peak Current: 32Amps
    Continuous Current: 16.5Amps
    Maximum Motor RPM: 2800

    Using a ruler on the photo I guestimate a 4:1 reduction.

    The result: 9.55 x 4 = 38.2

    2800 motor rpm/38.2 = 73 RPM Pedal Cadence.

    Thanks for the link.

    I learned a lot.
    Last edited: Jan 28, 2015
  10. KCvale

    KCvale Motorized Bicycle Vendor

    Yep, and the chain goes in serpentine around the CCW motor sprocket to catch enough teeth.

    Note the important part...

    Kit Specifications:
    Included Parts:
    360W Motor w/ Controller, Gearbox & 14T Freewheel Sprocket
    Motor Mounting Bracket w/ Spacers & Bolts
    44 Tooth Freewheeling Chainwheel
    Bottom Bracket Spindle
    Left & Right Crank Arms - 170mm

    Twist Grip Throttle
    2ea. Handlebar Grips
    2ea. Brake Handles w/ Motor Cutoff Switch
    Note that batteries are sold separately.
    Battery Connecting Harness

    A freewheel chainring/pedals combo to isolate motor power from your feet.
    If you value your feet and ankles at all DO NOT apply power directly to your pedals because you will eventually be paying hundreds if not thousands of dollars more than you saved in medical bills.

    I use motors with the same planetary gear box on it, the motors are just a bit longer, use an external programmable controller, and will take 24-48+V up to 1.8KW.
    The kicker is, these kits are $50 less
  11. boyntonstu

    boyntonstu Member

    To hub or not to hub?, that is the question.

    Is this too cheap?

    All the best!
  12. KCvale

    KCvale Motorized Bicycle Vendor

  13. boyntonstu

    boyntonstu Member

    I agree.

    Battery: I want to go this way:

    or solder using this:

    Last edited by a moderator: Dec 15, 2015